diagnostic medlab

Diagnostic Handbook The Interpretation of Laboratory Tests

Diagnostic Medlab Auckland

August 2000

Mike Gill Paul Ockelford Arthur Morris Tony Bierre Cam Kyle

First edition 1992

Second edition 1994

Third edition 2000

Copyright 2000 by Diagnostic Medlab Limited

No part of this publication may be reproduced by any process without written permission from

Diagnostic Laboratory Holdings Ltd.

PO Box 5728, Auckland 1,

New Zealand.

TERMS OF USE Use of and access to this handbook is subject to the following terms and conditions which you are deemed to accept by accessing this handbook: Use of Information We have developed this handbook to provide you with information relating to our services. The information in this handbook is general information only and is provided free to you. It is not intended as, nor is it capable of being, advice on any specific problem or a replacement for individual professional medical advice, opinions or therapies advised to you by your medical practitioner. We endeavour to keep the information in this handbook up to date however, we make no warranty as to the accuracy, reliability, suitability or currency of information in this handbook. All information in this handbook is subject to change at any time. Always seek the advice of a qualified medical professional before acting on the information in this handbook. Intellectual Property We own all copyright and other intellectual property rights in this handbook. All rights are reserved. You must not copy, display, modify, reproduce, store on a retrieval system, transmit (in any form or by any means), distribute, use for creating derivative works or use in any other way for commercial or public purposes, any part of this handbook without our prior written consent. OR Except where noted, you may download material for your personal, non-commercial use provided that you:

• retain all copyright and other proprietary notices on each copy; • use the material in a manner consistent with these terms of use; and • understand that no intellectual property rights or licences granted to our trade marks, trade names or

copyright material. Jurisdiction This handbook (and the services described in it) are only intended for persons resident in New Zealand. Any disputes between us will be resolved by the New Zealand courts. This handbook is governed by, and is to be interpreted in accordance with, New Zealand law. To the fullest extent permitted by law, we accept no responsibility for the compliance of the information in this handbook with the laws of any other country. Liability We will not be liable for any damages, losses (including, without limitation loss of profits, business or data), costs or expenses of any kind, which arise out of, or result from, any use of, or inability to use, this handbook.

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PREFACE TO THE FIRST EDITION The starting-point for this Handbook, which has been written for doctors, midwives, practice nurses, receptionists, laboratory staff, students, and other health care workers, was a file of questions phoned through to Diagnostic Medlab over the past decade or so. Often the question has been about a relatively minor abnormality: What does it mean? Can it be ignored? Should the test be repeated? When will follow-up be necessary? This may help to explain what might otherwise appear to be an unusually capricious selection of information. Once upon a time someone asked about it.

Along with the enormous increase in types of laboratory tests over the past 30 years there has been an increase in the sophistication we apply to interpretation of results. Age, sex, biological variation, posture, diurnal rhythm, pregnancy all have major effects quite apart from those of disease. Medications, singly or in combination, add a further set of variables; and any serious or even trivial illness can have non-specific effects on a wide range of laboratory values.

As well as presenting factual information, we have attempted, with some tests, to give an opinion on their value, particularly where their usefulness is limited or even non-existent. There will undoubtedly be errors and omissions; we apologise for these and for opinions which turn out to be wrong.

PREFACE TO THE THIRD EDTION

Comments received about the Handbook since the last edition was published in 1994 suggest that we have provided a useful resource for practitioners in primary health care, always our target audience. The more one works in the primary sector, the more one realises it is a different entity from secondary and tertiary healthcare where either the diagnosis is known before the patient reaches hospital or at least they have been recognised as being seriously ill. In primary healthcare the problems are often more nebulous. The serious acute problems are small in number beside those with vague symptoms which might be due to early disease, resolving disease, transient disease or sometimes no disease at all.

One of the roles of laboratory medicine is to look at the possibility of early disease and provide evidence for or against, before the classical picture has had time to develop. Many of the laboratory abnormalities themselves will be equivocal and a goal of the Handbook has been to help practitioners when deciding what to do next � treat, refer, investigate further, watch and repeat in weeks or months, ring and discuss with a pathologist � or no action at all.

When we first embarked on this edition we thought revision would be a simple process, an extra sentence here, a revised reference range there but laboratory medicine has, in the event, moved a long way, even in five years, and the text has grown by a third.

For this edition the contributors have been:

biochemistry Mike Gill Cam Kyle

cytology/histology Tony Bierre

haematology immunology

Paul Ockelford Mike Gill David Haines

microbiology Arthur Morris Selwyn Lang Rod Ellis-Pegler

The other contributors are all those general practitioners, practice nurses, midwives, and others, who have rung us at the laboratory to talk over a problem, ask for information, make a suggestion. Having entered the new millennium, the role of the laboratory is not just to provide a result but to help practitioner and patient understand what that result means. The Handbook will help, we believe, and beyond that we suggest a phone call to the pathologist - one of the quickest, simplest and most under-utilised of all consultations.

The last and most important acknowledgement is to Annie Curran for her painstaking care as she typed draft after draft after draft.

Mike Gill Editor August 2000

How To Use This CD ROM To find a Handbook entry, e.g. �CK (creatine kinase) total�, expand the �C' file by clicking on the plus sign (+) beside the C in the left-hand �Bookmarks� window. All the C items are now displayed. Use the scroll bar in the Bookmarks window to take you to �CK (creatine kinase) total�. Click the words �CK (creatine kinase) total�. Use the scroll bar in the right-hand window to take you through the pages of the CK entry. At the end of the CK entry are two lines in blue indicating hyperlinks. Clicking on the 2nd line for example takes you to "Myocardial Markers for Infarction". Clicking the - box beside �C� shrinks the C entries back to a single line.

Specimen Collection More detail than the minimum information provided can be obtained by ringing the lab or asking for our detailed Collection Manual.

Reference Ranges For the common analytes, reference ranges are roughly the same throughout New Zealand or, indeed internationally, but for hormones and other tests where methodology can vary from one lab to another, the reference ranges can differ quite markedly. Even within the same lab, ranges may change from time to time as new methods are introduced.

Reference ranges are at best only a guide and results which are found unexpectedly to lie outside their stated range should be treated with circumspection.

see also � Reference ranges and the concept of normality

Units S.I. units are used throughout.

Enzymes and some other tests, including some hormones and antibodies, are expressed in International Units (IU)/litre (L), or Units/litre or simply Units. IU/L are particularly misleading, implying as they do that the reference range given is applicable world-wide. The reality is that International Units for the same test can vary widely depending on the method used whilst still calling themselves IU/L.

Interfering Drugs

The lists are not meant to be complete but will cover the most common interferences. Additional queries about a specific drug/test combination should be directed to a pathologist.

Notes on Interpretation

These are not claimed to be comprehensive. Again, additional queries should be directed to a pathologist. Brief clinical details (usually one line only) help immeasurably with interpretation e.g. routine, wt-loss 1/12, pale and tired 3/12, on T4, on phenytoin, ? hepatitis and so on.

© 2000 Diagnostic Medlab View Terms of Use

A

Abiotrophia

Abiotrophia defectiva and A. adjacens

Nutritionally variant streptococci which need growth factors to support growth. An uncommon cause of endocarditis.

ABO type see Blood grouping

ABS see Antibacterial substance (ABS)


Accidental inoculation of infected blood see Needlestick injuries

ACE (angiotensin converting enzyme)

specimen: serum

Although ACE levels can be used in the diagnosis of sarcoidosis (two thirds of patients with active disease have elevated ACE), elevations are also found in other chronic inflammatory disorders, giving the test poor specificity.

Acetaminophen see Paracetamol (acetaminophen)

Acetone see Ketones

Acid-base investigations see Blood gases & pH

Bicarbonate


Acid-fast bacilli/infections see Tuberculosis (TB)

Tuberculin test (Mantoux test)

Acid phosphatase, prostatic (PAP)

specimen: serum

ref. range: males 0.1 � 0.6 U/L

Acid phosphatase is an obselete test and no longer available, PSA being a superior prostatic tumour marker. PAP is not usually elevated until a tumour has spread outside the prostatic capsule whereas PSA is usually elevated while the tumour is still localised to the gland.

Non-prostatic acid phosphatase is found in bone marrow, platelets, red cells and liver and can be elevated in diseases affecting these tissues.

Acinetobacter

A gram-negative bacillus commonly present in soil and water. In the hospital environment it is found in moist situations, tap water, hand basins and ventilator equipment. Acinetobacter species are opportunistic pathogens in the urinary tract, respiratory tract and on skin surfaces. They are occasionally associated with invasive processes. They have caused hospital epidemics. Infections are uncommon in the community. Acinetobacter is usually resistant to most antimicrobial agents but many strains are susceptible to trimethoprim/sulphamethoxazole. For serious hospital-acquired infection, imipenem is the drug of choice.


ACTH (adreno-corticotrophic hormone)

specimen: plasma (EDTA) Collect 0700 � 1000 hr along with simultaneous cortisol level.

ref. range: 2 � 11 pmol/L at 0700 � 1000 hrs

ACTH is elevated in primary adrenal insufficiency (Addison's disease).

It is not used in the early investigation of Cushing's syndrome (qv) but may help in evaluating proven hypercortisolism where a high ACTH suggests pituitary adenoma or, uncommonly, ectopic ACTH production, e.g. by small cell carcinoma of lung.

Actinomyces

An anaerobic gram-positive filamentous bacillus found as a normal commensal in the mouth and gut. The most commonly encountered species is A.israelii. Actinomyces species are susceptible to penicillin and doxycycline. Most isolates are resistant to metronidazole.

The most common form of infection is cervicofacial infection characteristically occurring in association with poor oral hygiene and tooth abscesses or decay. Thoracic and gastrointestinal infections also occur. All these deep seated infections may declare themselves by developing draining sinuses.

Actinomyces species also grow in association with IUCDs (intrauterine contraceptive devices). They may be detected in a cervical smear or by culture of a removed IUCD. Opinions vary as to what should be done when they are detected on a cervical smear in an asymptomatic woman. Although pelvic actinomycosis is well reported in association with IUCD use, the individual risk of infection with a colonised IUCD is small. There is no indication for antibiotic treatment in response to a positive smear alone. If the IUCD is left in place the woman should have the symptoms of infection


explained and follow-up must include enquiries about symptoms and a bimanual examination. If the IUCD is close to being replaced it may be prudent to remove it. One recommendation has been to remove the device, repeat the smear in 6 weeks - 6 months and reinsert if the smear is negative. There are, however, no data to show this approach prevents the development of pelvic actinomycosis and there is the risk of unwanted pregnancy while the IUCD is out.

Activated partial thromboplastin time see APTT (activated partial thromboplastin time)

Activated protein C resistance (APCr) specimen: plasma (citrate)

ref. range: 2.4 - 4.0

Activated protein C resistance occurs in patients with the Factor V mutation known as Factor V Leiden (FVQ506). This mutation is present in 5% of a normal Caucasian population. It is the commonest of the recognised thrombophilia markers. It is detected in 16-20% of consecutive patients presenting with thromboembolism but the frequency is higher in selected patient groups. Although it increases the thrombotic risk 5-10 fold, it is generally regarded as a relatively weak risk factor.

APCr is measured using an APTT ratio with and without activated protein C. The normal ratio is 2.4 - 4.0. Heterozygous positive patients with the Factor V mutation have ratios of 1.6 or less. Homozygosity, which is much less common, is associated with a higher thrombotic risk and a lower APCr.

see also Factor V Leiden (FVQ506)


Acute leukaemias

The diagnosis is usually obvious because of blast cells in the blood film, raised total white count, anaemia, thrombocytopenia and neutropenia, but one or more of these features can be absent at the time of diagnosis.

Acute lymphoblastic leukaemias (ALL)

The more common childhood leukaemia. Prognosis is relatively good in children with 80-90% remission rates and 50% cure. Remission rates are lower in adults.

Acute myeloid leukaemia (AML)

The more common leukaemia in adults. AML may arise de novo or through transformation of chronic myeloid leukaemia or myelodysplastic syndromes. Transformed AML responds poorly to treatment.

In de novo AML, first remission is achieved in 70-80% of patients with 30-40% long term survivors when treated with chemotherapy alone. With allogeneic bone marrow transplantation for patients aged less than 55 years there is a 50-60% five year survival.

The M3 subtype, acute promyelocytic leukaemia (APML), is treated with ATRA (a retinoic acid derivative) initially, to promote cell differentiation, followed by chemotherapy. This gives 85-90% remission rate with 80% 12-month disease free survival.


Acute phase proteins (reactants)

Following inflammation or tissue destruction there is an increase in the so-called acute phase proteins with the development of a typical pattern on serum protein electrophoresis.

analyte rise response time adult ref range

CRP up to 1000x 6-10 h <5 mg/La- 1 antitrypsin 2-4x 24-48 h 0.9-2.0 g/Lorosomucoid 2-4x 24-48 h 0.5-1.5 g/Lhaptoglobin 2-4x 24-48 h 0.3-2.0 g/Lfibrinogen 2-4x 24-48 h 1.4-4.5 g/Lceruloplasmin 1.5-2x 48-72 h 0.15-0.45 g/LC3 1.5-2x 48-72 h 0.55-1.2 g/LC4 1.5-2x 48-72 h 0.2-0.4 g/L

Plasma analytes which decrease with inflammation include albumin, transferrin, iron, total cholesterol and HDL cholesterol.

see also separate entries for each acute phase protein

Addison's disease see Adrenocortical insufficiency


ADH (antidiuretic hormone, vasopressin) ADH measurements are not easily available.

In suspected SIADH (syndrome of inappropriate ADH), urine osmolality, which correlates strongly with ADH, is a simpler and cheaper alternative.

Where there is difficulty separating pituitary-hypothalamic diabetes insipidus from that of renal origin, the response to exogenous ADH usually makes the diagnosis.

see also Osmolality, SIADH (syndrome of inappropriate ADH), Diabetes mellitus (DM)

Adrenal antibodies specimen: serum

Adrenal antibodies are present in 80% of autoimmune Addison's disease.

Adrenal medullary hormones see Catecholamines

HMMA (hydroxy methyl mandelic acid)

Metanephrines


Adrenocortical hormones

Hypofunction - see Addison's disease Synacthen stimulation test Hyperfunction - see Cortisol, serum, Cortisol, urine free Cushing's syndrome Dexamethasone suppression test Conn's syndrome Hirsutism/virilism Congenital adrenal hyperplasia (CAH)

Adrenocortical insufficiency

Addison's disease (primary insufficiency)

Usually autoimmune (70%), less often due to TB, haemorrhage, iron overload, HIV, infiltration.

Tests: � 0900 hrs cortisol (but 20-30% of Addison's have an 0900 cortisol within the reference range). � Synacthen test (qv) � an excellent test � ACTH (elevated) � plasma renin (elevated) � s. potassium (may be elevated) � s. sodium (may be decreased) � adrenal antibodies Secondary insufficiency: � hypopituitarism � suppression by long term steroid therapy


Adrenocortical hyperfunction see Cushing's syndrome

Conn's syndrome

Congenital adrenal hyperplasia (CAH)

Adrenocorticotrophic hormone (adrenocorticotropin) see ACTH (adreno-corticotrophic hormone)

Aeromonas Aeromonads are widely distributed in stagnant or flowing fresh water and in soil.

Human infections include:

• cellulitis or wounds contaminated with soil or water

• acute diarrhoeal disease � worldwide, affecting any age

• septicaemia

• other infections, including the urinary tract

Aeromonads are mostly resistant to the penicillins but are often susceptible to trimethoprim/sulphamethoxazole and quinolones, e.g. ciprofloxacin. Nalidixic acid or nitrofurantoin may be used for urinary tract infection. Although there are no data


on the benefits of treating Aeromonas associated diarrhoea, there may be benefit for those with severe disease. Options include cotrimoxazole or norfloxacin for three days.

AFP (alpha foetoprotein) specimen: serum

ref. range: adult non-pregnant <10 µg/L

AFP has two uses:

tumour marker � large elevations (>100) can be found in hepatomas and testicular tumours and are used for monitoring treatment and in diagnosis. Smaller non-diagnostic elevations are found in many forms of liver disease and malignancy.

screening for neural tube defects and Down's syndrome � serum AFP is measured in conjunction with hCG and oestriol to give a risk estimate. Definitive diagnosis requires measurement of AFP in amniotic fluid.

see Maternal serum testing for foetal Down's syndrome and neural tube defects (NTD)

AGA (antigliadin antibodies) see Gliadin (gluten) antibodies (AGA)


AHT (antihyaluronidase titre) A streptococcal antibody test that is no longer used.

AIDS see HIV (human immunodeficiency virus)

Alanine aminotransferase see ALT (alaninine transaminase or amino transferase)

Albumin specimen: serum

ref. range: 35 � 45 g/L

Decreases

• acute or chronic inflammatory illnesses

• urinary protein loss

• advanced liver disease

• gastrointestinal loss

• severe malnutrition

Increases are usually due to dehydration.


Alcaligenes

A gram-negative bacillus, part of the normal human flora. In hospitals it can be found in moist environments including respirators and haemodialysis systems. It is occasionally isolated from the urinary tract, ear discharges, wounds or sputa. Treatment is according to susceptibility testing, but on the basis of in vitro results, imipenem is likely to replace cotrimoxazole as the agent of first choice for serious Alcaligenes infection.

Alcohol, ethyl (ethanol)

specimen: serum / plasma (heparin) / whole blood

conversion factor 1mmol/L = 4.6 mg/100ml

17.4 mmol/L in whole blood corresponds to 20 mmol/L in serum or plasma.

ranges: legal limit while driving 17.4 mmol/L whole blood

fatal above 80 - 100 mmol/L

Alcohol is metabolised by the liver at a rate independent of blood alcohol concentration. Although there is wide individual variation, 10g alcohol/hour is an indicative figure. A 750 ml bottle of wine with an alcohol content of 12% (12g/100ml) contains 90g alcohol. For an individual metabolising at the indicative rate of 10g/hr, it would take 9 hours to clear the blood stream of alcohol - and 18 hours to clear two bottles.

A "standard unit" of drink contains 10g alcohol.

Identifying alcoholism


When considering the possibility of excessive alcohol intake, the two most useful markers are:

• GGT 50 - 200 U/L, occasionally up to 1000

After a heavy weekend's drinking, levels rise about 50%, peaking on about the third day.

An elevated GGT due to alcohol should fall by about half after two weeks abstinence and reach baseline by about six weeks.

• red cell MCV in the range 95 - 115 (ref. range 80 - 98) Other tests affected by alcohol include:

• other liver enzymes: alk. phos, AST, ALT, ratio AST/ALT >1.5

• triglyceride elevated � fatty liver

• urate elevated

• ferritin elevated � alcoholic hepatitis

• CK elevated � alcoholic myopathy

• thrombocytopenia


Aldosterone and renin, plasma specimens: plasma (EDTA), 2 tubes at room temp (must not be refrigerated).

The patient should have a normal sodium intake and have been ambulant at least 1-2 hours.

ref. ranges: aldosterone 100-850 pmol/L (standing) 50-450 pmol/L (recumbent)

renin 5-75 mU/L (ambulatory)

aldosterone/renin ratio <20 hyperaldosteronism unlikely>20 hyperaldosteronism possible

Effect of drugs: Spironolactone, which inhibits aldosterone formation, must be stopped six weeks before testing.

The test is fairly robust with other drugs but the aldosterone/renin ratio may sometimes be altered by:

loop diuretics, calcium antagonists � false high ratio

ß-blockers, NSAIDs, methyl dopa � false low ratio

ACE inhibitors lower the aldosterone/renin ratio in normals, but in those with Conn's syndrome, the ratio usually remains high.

Primary hyperaldosteronism (Conn's syndrome)


The basic pathology is an adrenal adenoma (2/3) or adrenal hyperplasia (1/3) causing:

• hypertension • hypokalaemia, with s. potassium classically <3.5 mmol/L but often in the range

3.5-3.9 mmol/L. • elevated aldosterone/renin ratio. This is the most sensitive test.

A positive screening test is an aldosterone/renin ratio >20 (usually >40). Typically the renin is suppressed to <15 mU/L and the plasma aldosterone is >600 pmol/L. Renin suppression by beta-blockers or NSAIDs may give a false positive screening test.

A negative screening test is a ratio <20, especially if the renin is >25 mU/L. A negative test is valid in patients who continue taking diuretics, ACE inhibitors or calcium-channel blockers.

Secondary hyperaldosteronism

This is found in oedematous and hypertensive states where the plasma aldosterone increase is secondary to an increased renin, e.g. diuretic therapy, renal artery stenosis.

Alkaline phosphatase (ALP) specimen: serum

ref. range:

Age male U/L female U/Lup to 10 y 30-350 30-35011-15 y 30-400 30-30016-20 y 30-200 30-25021-49 y 25-110 25-10050-60 y 25-120 25-120>60 y 25-130 25-130


The bone isoenzyme comes from active osteoblasts, hence high levels during childhood, pubertal growth spurt, healing fractures.

In the liver, ALP is found in biliary canaliculi, increased production being stimulated by biliary obstruction and to a lesser extent other liver pathology.

Causes of hyperphosphatasaemia can be grouped under three main headings:

Liver disease

ALP of liver origin is usually identified by an accompanying rise in GGT which is also an "obstructive" enzyme. AST and ALT are usually also elevated to varying extents in liver disease. For further discussion see liver enzymes.

Bone and other non-liver disease

• Paget's diseases of bone

• malignant disease, secondary or primary

• hyperparathyroidism

• rickets/osteomalacia

• chronic renal failure

• healing fractures

• thyrotoxicosis

• rheumatoid arthritis

• intestinal disease, e.g. Crohn's, ulcerative colitis

Benign isolated elevations of ALP

• Growth in childhood, particularly the pubertal growth spurt when levels can go up to 650 U/L.


• Third trimester of pregnancy, up to 400 U/L.

• Isolated elevations of ALP are common in the elderly and usually attributed to foci of subclinical Paget's disease provided there is no evidence of malignancy. Another possibility is osteomalacia due to vitamin D deficiency.

• In transient hyperphosphatasaemia of infancy and early childhood, ALP can go up to 3000 U/L for up to 3 months. Other liver enzymes remain unaffected. Aetiology remains obscure but viral infection is a possibility.

• Familial benign hyperphosphatasaemia shows as a raised ALP throughout life.

Alkaline phosphatase isoenzymes specimen: serum

Assessment of other laboratory tests and the clinical picture will usually explain elevations of ALP without resorting to isoenzyme fractionation � which usually provides a clear-cut answer only when the answer is already obvious.

A useful generalisation is that where both ALP and GGT are raised, liver is the source. When GGT is normal, the raised ALP is probably from bone.

Occasionally, however, the answer is not obvious. Heat stability is a method of isoenzyme analysis, the ALP being measured before and after 10 mins incubation at 56ºC.

% ALP remaining likely origin of raised ALPafter incubation <20% mainly bone 25-55% mainly liver and/or intestine >90% placenta


Allergy

These are all tests for Type I immediate hypersensitivity reactions mediated by IgE antibodies as seen in allergic rhinitis, anaphylaxis, allergic skin reactions, food allergies, drug allergies.

see Skin tests for allergy, RAST (Radioallergosorbent test) IgE total, Bee and wasp venom allergy, Food allergy Penicillin allergy, Anaesthetic allergy

Alopecia

The common age and gender related variant does not warrant laboratory investigation but specific aetiologies to be considered include:

• hypothyroidism

• hyperthyroidism

• drugs : cytotoxics, lithium

• dermatological pathology

• any severe illness

• zinc deficiency

• warfarin hypersensitivity (rare)

• polycystic ovary syndrome

When associated with a severe but correctable illness, the alopecia is likely to be transient.


ALP see Alkaline phosphatase isoenzymes

alpha-1-antitrypsin see Antitrypsin (alpha-1-antitrypsin - AAT)

alpha-foetoprotein see AFP (alpha foetoprotein)

17 alpha-hydroxy progesterone (17-OHP) see 17 alpha-hydroxy progesterone (17-OHP)

ALT (alaninine transaminase or amino transferase) specimen: serum

ref. range:


Age (yrs) U/Lfemale male

0-20 35 4021-60 40 45>60 35 40

Also called SGPT or GPT.

ALT elevations, which are common and usually accompanied by other enzyme elevations, are found in:

• liver disease, other system diseases, drugs see Liver enzymes

• AST/ALT ratio � in healthy persons the average ratio is about 1.3. In chronic liver disease (including alcoholic hepatitis) the ratio tends to rise whereas in acute viral hepatitis, the ratio tends to fall.

• obesity � up to 50% higher in moderately obese and up to 300% in the extremely obese male.

• skeletal muscle damage � see CK-MB in myocardial infarction (MI) for a list of conditions to be considered. ALT elevations are much smaller than those of CK but if only the ALT has been tested, a myopathy or myocarditis can be missed.

• idiopathic � where no cause has yet been found.

Aluminium specimen: blood in trace metal tube (navy blue stopper)

ref. ranges: <2.2 µmol/ acceptable>3.7 µmol/L at risk>7.4 µmol/L dangerous


Used to monitor dialysis patients using aluminium hydroxide. In the past, aluminium accumulation sometimes led to dementia and osteomalacia but with monitoring this no longer occurs.

Aluminium-containing antacids in non-dialysis patients, aluminium kitchenware, or working with aluminium, do not cause measurable increases in serum aluminium. Some patients with Alzheimer's disease have increased aluminium deposits in the CNS but serum tests will not detect this.

Amenorrhoea

Consider:

� pregnancy � an hCG is the first test in the investigation of amenorrhoea � polycystic ovary syndrome � hyperprolactinaemia � thyroid disease � premature ovarian failure: FSH and LH elevated � adrenal disease • drugs � oestrogens and/or progestagens � post-oral contraceptives � anabolic and other steroids � stress, including chronic disease � eating disorders � intense athletic training

American units for cholesterol and glucose see SI (systeme internationale) units


Amikacin see Antibiotics, serum levels

Amino acids specimen: serum

or urine, fresh random specimen for screen test

For specific amino acids, e.g. phenylalanine monitoring in phenylketonuria (qv), a dried blood spot on a Guthrie card is often adequate.

Aminoglycoside, serum levels see Antibiotics, serum levels

Aminophylline see Theophylline (Nuelin)

Amiodarone specimen: serum

therapeutic range: 1.5 � 3.9 µmol/L (trough level)


Amiodarone, which is rich in iodine (1/3 by weight), blocks conversion of thyroxine (T4) to tri-iodo thyronine (T3) causing high free T4 (up to 50 pmol/L) and low free T3 in many patients. TSH often rises early up to 10-15 mU/L but should return to normal within 3-4 months except in the small percentage of patients where hyper- or hypo-function develop.

Amitriptyline see Antidepressant drugs, tricyclic

Ammonia

specimen: whole blood (heparin) collected without haemolysis, transported on ice and analysed promptly.

ref. ranges: macro-collect <70µmol/L micro-collect <115 µmol/L

A specialist test sometimes used in hepatic failure, Reye's syndrome and some inborn errors of metabolism.

Amoeba see Entamoeba coli


Amphetamine see Drug screen � pre-employment screen and drugs of abuse

Amylase, serum specimen: serum ref.range: 25 - 135 U/L

Amylase, found mainly in pancreas and salivary glands, is used in the differentiation of acute pancreatitis from other causes of the acute abdomen.

In acute pancreatitis, amylase typically rises above 400 U/L, returning to normal in about 4 days.

The enzyme pattern is inconsistent, however, and failure to detect an elevation does not preclude the diagnosis even when there is severe infarction.

Acute peritonitis, causing inflammation of the serosal surfaces of the pancreas and other organs, can elevate amylase but usually not above 400 U/L.

Other causes of hyperamylasaemia include mumps, diabetic ketoacidosis, biliary tract disease, renal insufficiency, shock, some drugs (particularly narcotics), hypoxia, pelvic infection, macroamylasaemia.

Chronic pancreatitis does not raise amylase except sometimes during acute exacerbations.

In macroamylasaemia, as in other macromolecular enzyme variants, a consistently elevated enzyme level is found in a well person. A definitive diagnosis can be made using the amylase/creatinine clearance ratio, ACCR.

ACCRur amylases amylase

xs creatinineur creatinine

x(%)..

..

= 100


In macroamylasaemia, the ACCR is <2%. The usual reference range is 2-5%.

Amylase, urine specimen: random or 24-hr urine without preservative ref. range: <650 U/L or U/day

Urine amylase is elevated in all conditions where serum amylase is raised except renal failure and macroamylasaemia. It is not often used except perhaps in the diagnosis of macroamylasaemia where the ACCR is calculated.

see Amylase, serum

ANA (antinuclear antibodies) specimen: serum

Interpretation:<1:40 negative1:40 or 1:80 borderline>1:160 consistent with auto-immune disease

but not diagnostic

In SLE (systemic lupus erythematosus)

The main indication for ANA is as a screen test in suspected SLE where it will be positive in 95% of cases. A negative ANA makes SLE unlikely. A positive ANA requires follow up by anti-DNA, which has a much higher specificity for SLE, and ENA to check specificity of the antibody.

see SLE (systemic lupus erythematosus)


DNA, paternity ENA (extractable nuclear antigen) antibodies

ANA in healthy people

The exact incidence of positive ANAs in healthy populations depends on gender (commoner in women) age-group (rises with age) test methodology, ethnicity etc. and for this reason precise figures are not available.

A commonly quoted overall incidence is 5%.

A recent study narrowed this to 5% in women age 40 - 50.

Another quotes 20% in women over the age of 60 rising to 30% over age 80.

The only certain statement is that positive ANAs are fairly common in healthy people and should never, as an isolated finding, be represented as possibly indicating SLE which requires additional laboratory and clinical features before the diagnosis can be made.

see SLE (systemic lupus erythematosus)

ANA in other autoimmune disorders

Incidence of positive ANA in other conditions:

rheumatoid arthritis 30% Sjogren's syndrome 60% limited scleroderma (CREST) 50% diffuse scleroderma (systemic sclerosis)

80%

mixed connective tissue disease (MCTD)

80%


polymyositis 30% autoimmune liver disease <10%

Drugs causing positive ANA and sometimes a lupus-like illness

• procainamide � responsible for most drug-related SLE

• anticonvulsants

• isoniazid

• hydralazine

• chlorpromazine

• methyldopa

The clinical manifestations of drug-related SLE are mild and subside within six weeks of drug withdrawal.

ANA patterns

ANA is detected by adding patient serum to a layer of cells on a slide, then adding a fluorescent detection system. If ANA is present it shows up as a fluorescent pattern illuminating various nuclear structures. Usually the pattern is not specific for a particular disorder but associations have been suggested:

nucleolar pattern � diffuse scleroderma

centromere � limited scleroderma, CREST

speckled � MCTD, Sjogren's, polymyositis, RA

peripheral, diffuse � SLE

(homogeneous)


Anaemia Anaemia is a reduction of the Hb concentration below the 95% reference range selected for age and sex.

see Blood count for Hb reference ranges.

A full classification of anaemia encompasses the whole discipline of haematology but there needs to be a starting point and a simple one is the morphological classification based on MCV (mean red cell volume), measured in femtolitres. The usual MCV reference range is 80-98 fl. There are, of course, big overlaps between the three divisions � acquired microcytic or macrocytic conditions will have started in the normocytic range before moving in the direction of an MCV outside the reference range. Investigating an anaemia

Anaemia is probably the commonest of all laboratory abnormalities and investigations should proceed logically, starting with the most probable causes of anaemia for that person's age, sex and clinical findings, proceeding through the less common abnormalities, and ending with a phone-call to the haematologist if the cause


is not apparent after the first couple or so rounds of investigation. Here are some early questions/tests to consider:

• are there any other diagnostic haematological abnormalities in blood film, white cells or platelets?

• does the patient have a history or clinical findings of an illness that can cause anaemia?

• drug history

• ferritin � iron deficiency is the commonest cause of anaemia. Ferritin should be a routine test in all menstruating women and in anaemias in other patient groups where the aetiology is not yet known.

• vitamin B12 and folate � though deficiencies are much less common than iron deficiency

• creatinine � renal impairment is typically silent and is almost invariably accompanied by anaemia

• ESR and/or CRP looking for inflammatory disease

• serum protein electrophoresis and immunoglobulins

• TSH for hypo- and occasionally hyper-thyroidism

• liver enzymes

• reticulocytes and haptoglobulins as a screen for haemolysis

• thalassaemia screen for the disproportionately microcytic film

• hCG if pregnancy is a possibility

Anaemias of chronic disease

These are typically normocytic, normochromic anaemias but there may be mild microcytosis and hypochromia.


They are often multi-factorial. For example in the anaemia associated with rheumatoid arthritis, iron uptake into erythroblasts is inhibited and the anaemia will be unresponsive to iron therapy - except when there is iron deficiency due to chronic blood loss secondary to analgesic use. And the anaemia of renal insufficiency is due to a combination of reduced erythropoietin, shortened red cell survival and sometimes GI or gynaecologic bleeding.

Common causes of anaemia of chronic disease: � renal insufficiency � there is a rough correlation between elevation of s. creatinine and anaemia. � rheumatoid arthritis � other connective tissue diseases � chronic infections � malignancy � chronic liver disease � endocrine deficiencies � hypothyroidism (occasionally hyperthyroidism) � hypopituitarism � hypoadrenalism � hypogonadism

Anaerobic infections Anaerobic organisms, which are widely distributed in soil and as part of the normal flora of mouth, gut, and vagina, grow readily in deeply-placed abscesses in the abdomen, wounds, pleural cavities, brain, oropharynx and in peritonitis or endometritis. Foul-smelling discharge indicates anaerobic infection.

Routine cultures do not grow anaerobes which require special media and an oxygen-reduced environment. Anaerobic cultures are set up only on specific request or when clinical details indicate the need for them. Swabs are not the ideal specimen, tissue obtained at debridement being the ideal. Aspirated pus or fluid is best collected and transported in a syringe which should not be refrigerated. IUCDs (intrauterine contraceptive devices) are routinely cultured for Actinomyces.


Common anaerobic species are Bacteroides, Fusobacterium, Actinomyces and Clostridium.

Most of the anerobes we isolate will be susceptible to amoxycillin - clavulanate, clindamycin and metronidazole.

Anaesthetic allergy

Allergy to local anaesthetic is rare but often suspected by patients who may request skin tests in a specialist allergy laboratory to exclude the possibility � before dental anaesthesia for example.

Reactions to other allergens can occur under general anaesthesia, particularly to muscle relaxants and the latex of surgical gloves.

Analytical variation or error see Variation Errors

ANCA see Antineutrophil cytoplasmic antibodies (ANCA)

Ancylostoma duodenale


see Hookworm

Androgens see Testosterone DHEAS (dehydroepiandrosterone sulphate) Androstenedione

Androstenedione specimen: serum ref. range: adult female 3.5 - 9.0 nmol/L adult male 3.0 - 8.5 nmol/L

Androstenedione is secreted by the adrenal cortex, testis and ovary and is a precursor of testosterone and oestrone. In pre-menopausal women, the adrenal cortex and ovaries contribute equally but after the menopause androstenedione is almost entirely of adrenal origin.

In hirsutism and polycystic ovary syndrome it can be elevated but testosterone is the preferred test.

Androstenedione can be markedly elevated in adrenal hyperplasia and is used in the investigation of virilism.

ANF (antinuclear factor)


see ANA (antinuclear antibodies)

Angioedema see Complement, C1 inhibitor (C1 INH)

Angiotensin converting enzyme see ACE (angiotensin converting enzyme)

Anion gap specimen: serum

ref. range: 8 � 16 mmol/L

The anion gap is a simple calculation which, if increased above 16 mmol/L, gives a crude (very crude) indication of metabolic acidosis as in salicylate or methanol poisoning, ketoacidosis, lactic acidosis, renal acidosis.

The calculation and its derivation are as follows:

In serum, total anions = total cations

C1- + HCO3- + acid anions (the anion gap) = Na+ (the major cation)

anion gap = Na+- (C1- + HCO3-)

For example a patient with salicylate poisoning might have


Na+ = 146, C1- = 100, HCO3- = 16

The anion gap, at 30 mmol/L is increased, with acidic salicylate anions being the cause of the increased gap.

Ankylosing spondylitis A seronegative spondyloarthropathy causing low back pain and reduced spinal mobility due to sacroileitis and spondylitis. Typically it occurs in younger males with 95% positivity for HLA B27 (qv).

Anorexia nervosa and bulimia Laboratory abnormalities include:

• hypokalaemia is common in both conditions and can be profound (<2.0) in bulimia due to the combination of vomiting and use of laxatives. In this situation there may be a metabolic alkalosis with raised serum bicarbonate.

• anaemia (normocytic)

• low FSH/LH accompanying the amenorrhoea which is almost invariable in anorexia.

• hypoalbuminaemia, particularly when there is oedema.

• hypocalcaemia is uncommon but is found occasionally.

• cortisol may be elevated

Other wasting disorders need to be excluded:

� glucose to exclude diabetes � TSH/T4 to exclude hyperthyroidism


� Addison's disease causes wasting but is rare in young women under the age of 25 which is the common age group for eating disorders.

Antenatal group, first visit specimen: 1 tube serum + 2 tubes EDTA whole blood

tests: • CBC• ABO and Rh group• red cell antibodies• hepatitis Bs antigen• rubella antibodies• syphilis antibodies

Antenatal group, follow-up visit specimen: 1 tube serum + 1 tube EDTA whole blood

tests: • CBC• red cell antibodies

Antiarrhythmic drugs specimen: serum

therapeutic ranges:


Drug umol/Lamiodarone 1.5-3.9disopyramide 6-15flecainide 630-2100lignocaine 6-21procainamide 15-37quinidine 7-15mexiletine - therapeutic 3-11 toxic >16propranolol 200-390

Antibacterial substance (ABS) Finding ABS in a urine usually indicates antibiotic therapy and provides an explanation for sterile pyuria (qv), if present.

see also Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections).

Antibiotics, serum levels specimen: serum

collection times: trough = just before dose

peak = IV bolus 15 mins after dose

IV infusion 1 hr after dose

IM or oral 1 hr after dose

Aminoglycosides

Therapeutic ranges for aminoglycosides when given 8-hourly:


Drugpeak trough

amikacin 20-30 <10gentamicin 5-10 <2netilmicin 5-10 <2tobramycin 5-10 <2

mg/L

If gentamicin is given as a single daily dose (4-5 mg/kg/day) the trough level should be <0.5 mg/L. Peak levels are not necessary for single daily dosing.

Vancomycin Trough levels should be <15 mg/L. It is seldom necessary to do peak levels.

Antibody screen in pregnancy see Red cell antibodies

Anticardiolipin see Cardiolipin antibodies (aCL)

Anticholinesterase insecticides see Cholinesterase


Anticoagulant therapy using warfarin see INR (international normalised ratio)

Anticoagulant therapy see Heparin therapy

INR (international normalised ratio) for warfarin therapy

Anticonvulsants specimen: serum

time of collection: quoted therapeutic ranges refer to trough levels. Specimens must be collected at least 8 hours after last dose, preferably just before next dose e.g. delay morning dose until after morning blood collect.

Drug Therapeutic Half-liferange (µmol/L) (hours)

carbamazepine (Tegretol) 16-40 20clobazam (Frisium) 800-1600clonazepam (Rivotril) 70-230 40ethososuximide (Zarontin) 300-700 30phenobarbitone 65-170 100phenytoin (Dilantin) 40-80 30primidone (Mysoline) measured as phenobarbitonevalproic acid (Epilim) 350-700 13

Indications for monitoring anticonvulsants vary between the different drugs.


Suggested guide-lines:

• monitoring initial stabilisation or change of dose � phenytoin, carbamazepine, phenobarbitone

• suspected toxicity � all drugs

• suspected non-compliance � all drugs

• failure to control seizures � all drugs

• ongoing routine monitoring � phenytoin only, and even this may not be essential.

The therapeutic range is a guide only. Levels below the range may control seizures; levels above the range may not be toxic and may be necessary for control. When changing doses, retesting should be delayed a week or so till a new equilibrium develops.

Phenytoin, carbamazepine and phenobarbitone are potent inducers of hepatic enzymes thereby raising serum levels of GGT and ALP. The raised enzymes are regarded as an acceptable side-effect.

Primidone (qv) is measured as phenobarbitone which is the active metabolite.

For more details, see under separate drug entries.

Antidepressant drugs, tricyclic specimen: serum

Overdose screen Detects overdose of amitriptyline, nortriptyline, imipramine, desipramine, trimipramine, protriptyline, doxepin or dothiepin, but is nonspecific.


Therapeutic monitoring These drugs are not monitored routinely but estimations may be useful where there is lack of therapeutic response or uncertain compliance.

Therapeutic ranges:

Drug nmol/Lamitriptyline 550-1290clomipramine 830-2000desipramine 470-1130doxepin 550-1300imipramine 610-1670nortriptyline 280-570protriptyline 430-1430trimipramine 400-1000

The method is generic for all tricyclics so cannot distinguish one drug from another. Knowing which drug has been given is essential when assessing whether a level is in the therapeutic range.

Antidiuretic hormone see ADH (antidiuretic hormone, vasopressin)

AntiDNA see DNA antibodies (anti-double-stranded DNA)


AntiDNAse see Streptococcal antibodies (ASK, ASOT, ADNAse)Streptococcal antibodies (ASK, ASOT, ADNAse)

Antiendomysial antibodies (EMA) see Endomysial antibodies (EMA)


Antigliadin antibodies (AGA) see Gliadin (gluten) antibodies (AGA)

Antihyaluronidase titre (AHT) see Streptococcal antibodies (ASK, ASOT, ADNAse)

Antimicrobials see Antibiotics, serum levels

Antimitochondrial antibodies see Mitochondrial antibodies

Antineutrophil cytoplasmic antibodies (ANCA) specimen: serumref. ranges: not present in unaffected people

>1:160 is significantly positive


As their name indicates, these autoantibodies are directed against the cytoplasm of neutrophils.

Their presence indicates vasculitis including:

� Wegener's necrotising granulomatous vasculitis � systemic vasculitis � focal necrotising glomerulonephritis with vasculitis

An initial ANCA screen test has 95% sensitivity for these conditions and is followed by the more specific antiproteinase 3 (PR3) and myeloperoxidase (MPO) tests.

Antinuclear antibodies see ANA (antinuclear antibodies)

Antiphospholipid antibody syndrome (APS)

A syndrome characterised by widespread, recurrent arterial and venous thromboses causing ischaemia in the affected organs. Clinical presentations include:

� recurrent foetal loss, frequently mid-trimester with placental infarcts

� recurrent arterial or venous thrombosis

� stroke at a young age


� other neurological and cardiological presentations

APS is found frequently in SLE. When it occurs independently it is known as the primary antiphospholipid syndrome.

Markers used in the diagnosis of APS are autoantibodies directed against phospholipids, the main ones being:

· cardiolipin (qv) antibodies which are used as the initial test when APS is suspected · lupus anticoagulant (qv) · biological false positive RPR/VDRL

The aetiology of these antibodies, which may be transient, is unknown but the presence of elevated titres of anticardiolipin antibodies and/or the lupus anticoagulants, six months after an episode of venous thromboembolism is a predictor for an increased risk of recurrence with probable benefit from long-term oral anticoagulation therapy.

see Cardiolipin antibodies (aCL) Lupus anticoagulant (LAC) Hypercoagulability

Antistreptokinase see Streptococcal antibodies (ASK, ASOT, ADNAse)

Antistreptolysin-O-titre (ASOT)


see Streptococcal antibodies (ASK, ASOT, ADNAse)

Antithrombin III (ATIII, antithrombin)

specimen: plasma (citrate) ref. range: functional assay 80-120% immunological assay 70-140%

Antithrombin III is a non-vitamin K dependent physiological inhibitor of coagulation. It is essential for the anticoagulant effect of heparin.

Deficiency of ATIII, transmitted as an autosomal dominant, is associated with venous thrombosis. It is a strong but uncommon risk factor which accounts for <5% of patients with thrombophilia. The approximate incidence of the deficiency state is 1:5,000. Thrombosis occurs in 50% of patients before age 40. It is usually an indication for life long anticoagulant therapy after a thrombotic event.

ATIII can be spuriously reduced in the presence of heparin and after a thrombotic event, as well as in nephrotic syndrome, liver disease and pregnancy. Elevated levels are of no clinical significance.

Antitrypsin (alpha-1-antitrypsin - AAT) specimen: serum

ref. range: 0.9 - 2.0 g/L

AAT deficiency in its severe forms predisposes to early onset emphysema and juvenile cirrhosis and should be sought in these situations.


Sometimes the deficiency is detected as an absent or markedly reduced alpha-1 band on routine serum protein electrophoresis.

Genetically there is one normal gene, M, and two abnormals, S and Z.

Genotype Prevalence Reduction AAT% level (%)

MM 88 0MS 7 20MZ 4 40SS 1 40SZ 0.1 70ZZ 0.03 90

ZZ, and to a lesser extent SZ are associated with emphysema and cirrhosis, and both smoking and alcohol should be strongly discouraged. The importance of MS, MZ and SS is uncertain but avoiding smoking is a wise precaution.

Tests for AAT deficiency: Protein electrophoresis � a crude screen test but an absent or reduced alpha-1 band, or a band of slow mobility, is often the first clue to AAT deficiency.

AAT quantitation � a result of <1.0 g/L is suspicious and requires pheno-typing which gives the best measure of risk.

APCr see Activated protein C resistance (APCr)e


Apolipoproteins specimen: serum

Cholesterol and triglyceride particles in serum are coated with apoproteins to render them soluble. Quantitation of the various apoproteins provides a more sophisticated basis for classifying the hyperlipoproteinaemias but in Auckland at present they are not used routinely, classification being based on the simpler (and cheaper) measurements of total and HDL cholesterol and fasting triglyceride. As a generalisation, Apo-B is associated with LDL cholesterol and apo-A with HDL.

APTT (activated partial thromboplastin time)

The APTT is a basic test used to detect abnormalities of coagulation involving the intrinsic pathway. It is used to screen for deficiencies of plasma coagulation factors (except Factors VII and XIII) or for the presence of an acquired inhibitor. The '1+1' test is performed to distinguish between a deficiency and an inhibitor.

The APTT is usually sensitive to factor deficiencies <40% normal. It is most commonly prolonged by deficiencies of contact factor FXII, FVIII (reduced in classical haemophilia and von Willebrand's disease) and Factor IX (haemophilia B or Christmas disease).

Marked prolongation of the APTT (>80 secs) is usually due to haemophilia if the patient presents with bleeding, or due to Factor XII deficiency if the patient is asymptomatic.

The lupus anticoagulant, found in the antiphospholipid antibody syndrome (qv), can prolong the APTT markedly. It is usually associated with an increased thrombotic tendency rather than bleeding.

Heparin therapy


The APTT is used to monitor standard or unfractionated heparin but not low molecular weight heparin (LMWH) therapy.

Arcanobacterium haemolyticum

Previously called Corynebacterium haemolyticum. It is a gram-positive bacillus which causes pharyngitis and cutaneous infections. Acute pharyngitis due to A. haemolyticum is indistinguishable from that caused by S. pyogenes (Group A streptococci). In nearly half of all reported cases a maculopapular exanthem is present which resembles the rash of scarlet fever. Pharyngitis occurs mainly in adolescents and young adults. No prospective trials have been performed to see if therapy offers any benefit. A. haemolyticum is susceptible in vitro to erythromycin, clindamycin and tetracycline; penicillin susceptibility is variable. Cotrimoxazole resistance is common. Pencillin treatment failures have responded to erythromycin.

Arsenic Acute poisoning

specimens: random urine

and whole blood (heparin)

Chronic exposure

specimen: 24 hr-urine with 10 ml HCl in plastic container

or early morning urine collected at end of working week

ref. range: normal <0.7 µmol/L toxic >1.3 µmol/L

Arsenic is the 20th most common element in the earth's crust and is found in most living organisms and in low concentration in water. Because a high urine level can be


due to non-toxic organic arsenic found in relatively high concentrations in fish and shellfish, a high result should be repeated 2-3 weeks after abstaining from seafood. Industrial exposure to toxic inorganic arsenic occurs in users of arsenical pesticides and in the metal and marine paint industries.

Arthritis

Some of the diagnoses and tests to be considered include:

- septic arthritis � immediate joint aspiration (see Synovial aspirate) will give definitive diagnosis of septic arthritis and differentiate it from gout

- gout and pseudogout � see Synovial aspirate and Uric acid - rheumatoid arthritis, SLE and other connective tissue diseases. see under

disease heading - reactive arthritis � see Arthritis, reactive

Arthritis, reactive

Reactive arthritis is an aseptic arthritis that develops after an infection elsewhere in the body.

� post-enteric – Yersinia – Chlamydia – Campylobacter – Salmonella – Brucella � post-venereal – Chlamydia – Ureaplasma

Reiter's disease, which includes arthritis, conjunctivitis, and urethritis, is an example of a reactive arthritis. 60 - 90% of affected patients are positive for HLA B27 antigen (qv).


Ascorbic acid (Vitamin C) specimen: whole blood (EDTA or heparin)

ref. range: 20 � 80 µmol/L

This test for suspected vitamin C deficiency is rarely indicated.

ASOT (antistreptolysin O titre) see Streptococcal antibodies (ASK, ASOT, ADNAse)

Aspartate transaminase see AST (aspartate transaminase)

Aspergillus

A fungus common in soil and decaying material and the cause of an invasive disease in immuno-compromised patients. Diagnosis is by demonstration of hyphae in tissue biopsy, sputum or culture.

We often recover A. fumigatus and occasionally other Aspergillus species from ear swabs taken from patients with otitis externa. There is no easily applied antifungal agent for this situation. Management requires thorough debridement and keeping the ear dry. Adequate ear toilet is often possible only at an ENT clinic.


Allergic pulmonary aspergillosis is characterised by asthma and eosinophilia. The total IgE level is often above 1000 IU/L. Aspergillus precipitins should be tested for and skin prick testing arranged.

Aspirated fluids, synovial, pleural, ascitic etc

Culture and microscopy Collect the specimen into two vacutainer tubes: � plain tube (no additive) � citrate tube � the citrate acts as an anticoagulant and makes microscopy easier. If the volume of specimen is small, (<1ml) collect it all into the plain tube. Cytology There are two methods of preservation: � add up to 25ml aspirate or fluid to 3ml 3.8% sodium citrate or 20ml EDTA. Submit to lab as soon as possible, storing in fridge meanwhile; or � add 50-75ml fluid to an equal volume of ethyl or methyl alcohol and add 3 units

of heparin/ml body fluid. Submit to lab as soon as possible, storing in fridge meanwhile.

see also Synovial aspirate

AST (aspartate transaminase) specimen: serum

ref. range:


Age (yrs) U/L

0-1 30-100 2-10 20-8011-18 10-60>18 5-45

AST is found in high concentrations in liver, skeletal muscle and cardiac muscle. It is also found in red cells and small increases (up to 100 U/L) are found in haemolysed specimens or those left standing for more than 6 hours after collection. Small increases may be seen in the last trimester of pregnancy.

for more detail see Liver enzymes

Myocardial enzymes

ALT (alaninine transaminase or amino transferase)

ATIII see Antithrombin III (ATIII, antithrombin)

Atypical pneumonia see Pneumonia

Mycoplasma pneumoniae

Legionella

Psittacosis (Chlamydia psittaci)

Chlamydia pneumoniae


Autoantibodies specimen: serum

The list of autoantibodies used in the diagnosis of autoimmune disorders continues to lengthen.

Specificities for particular diseases are seldom absolute and low titre auto-antibodies can be found in apparently disease-free people. Observation over months or years may show regression, no change or progression to clinical disease.

Each autoantibody is described in more detail under its own alphabetic entry.

For more detail see table below


Tissue disease autoantibody

adrenal cortex Addison's disease adrenal

islet cells Type I diabetes GAD

IA2

islet cell (ICA)

insulin (IAA)

thyroid hypothyroidism microsomal

thyroglobulin

Grave's disease TSH receptor

gastric pernicious anaemia intrinsic factor

parietal cell

small intestine coeliac disease gliadin (AGA)

endomysial (EMA)

reticulin

liver autoimmune hepatitis smooth muscle (SMA)

1° biliary cirrhosis liver kidney microsomal (LKM)

mitochondrial (AMA)

neuromuscular myasthenia gravis acetylcholine receptor

kidney Goodpasture's syndrome glomerular basement membrane

crescentric glomerulonephritis

testis seminal infertility sperm

skin pemphigus pemphigus

haematological ITP platelet antibodies

post-transfusion red cell

lymphocyte

antiphospholipid (APS) cardiolipin

connective tissue disease rheumatoid arthritis rheumatoid factor

SLE ANA

polydermatomyositis ds DNA

scleroderma ENA

mixed CTD neutrophil cytoplasm (ANCA)

Sjogren's syndrome

vasculitis


B

ß see beta

B12 see Vitamin B12

Bacterial swabs

Bacterial specimens are collected for identification of microorganisms and for antibiotic susceptibility testing. The quality of the specimen is all-important and will determine whether a pathogen is successfully isolated or whether a false negative culture occurs.


Human pathogenic bacteria like a moist environment, close to body temperature (37°C) with no exposure to toxic chemicals. Conversely they are killed by:

� drying � sunlight � high temperatures � antiseptics � low temperatures � antibiotics

To provide an optimum environment for swabs, we place them in transport medium which should be stored at room temperature rather than at 4°C in the fridge. Gonococci, for example, survive 24 hours in transport medium at room temperature but only 2 hours at 4°C.

An exception is urines which should be stored in the fridge to prevent overgrowth of contaminants.

Details about collecting swabs from specific sites will be found under their own alphabetic headings.

� cervical � skin � ear � sputum � eye � throat � nasal � urethral � rectal � vaginal

Bacterial vaginosis see Vaginal discharge

Bacteroides


An important group of anaerobic gram-negative bacilli. B. fragilis, which is part of the normal flora of the bowel, has the ability to form abscesses when released into the peritoneal cavity. Specimens from intra-abdominal sites must always be cultured anaerobically as well as aerobically. Septicaemia and puerperal or post-abortion sepsis often include B. fragilis as a major pathogen.

Bacteroides fragilis produces beta-lactamase which inactivates pencillin and amoxycillin. Amoxycillin-clavulanate, metronidazole and clindamycin are the most effective agents.

Bacteroides other than B. fragilis are grouped as Bacteroides species. Some may be sensitive to penicillin. Antibiotic susceptibility testing should be discussed with a clinical microbiologist.

Some species in the genus have recently been reclassified as Prevotella and Porphyromonas species.

Barbiturates see Phenobarbitone (anticonvulsant monitoring)

Drug screen � pre-employment screen and drugs of abuse

Bartonella henselae see Cat scratch disease

Base excess


see Blood gases & pH

Basophils specimen: whole blood (EDTA) ref. range: 0-0.20 x 109/L The basophil count is part of a routine blood count (qv).

Basophilia is rare as an isolated abnormality. Increases occur in chronic myeloid leukaemia and other myeloproliferative disorders including polycythaemia rubra vera.

Bee and wasp venom allergy

These tests are generally done in a specialist rather than general laboratory setting.

The tests are of two sorts:

• skin prick testing

• specific IgE antibodies (RAST tests)

Tests are done for:

� honey bee � paper wasp (polistes) � German or common wasp (vespula)

Of the two, skin tests are the more sensitive and are preferred when performed by an experienced allergist. A negative result using allergen at a concentration of 7µg/ml


makes it unlikely that there is important allergy or that immuno-therapy will be required.

RAST tests are graded on a scale 0 to 4+ with a crude correlation between the result and the severity of the patient's response.

Clinically the allergic response varies from local pain and inflammation at the site of the sting, through an extended local reaction over a larger area, to a generalised anaphylactic response with urticaria, flushing, angio-edema, and sometimes severe bronchospasm and cardiovascular collapse. Any generalised response requires referral to a specialist allergy physician for consideration of immunotherapy (desensitisation) which can be highly effective.

Bence Jones protein (BJP)

specimen: random urine or 24-hr urine for quantitation when monitoring myeloma ref. range: not present in normal urine

In 1848, Bence-Jones described a protein in the urine of myeloma patients that precipitated at 50°C and redissolved on boiling. It consists of free light chain fragments (kappa or lambda) derived from IgG and IgA paraproteins found in serum in myeloma and occasionally from an IgM lymphoma-associated paraprotein. Because free light chains are small molecules they pass through the glomerular filter whereas the larger paraprotein molecules are usually retained in serum.

Presence of BJP in urine is an indication that a paraprotein is malignant rather than benign. In Bence Jones (light chain) myeloma there is no paraprotein in serum but a heavy band of free light chains in urine which means that testing for myeloma must include urine as well as serum electrophoresis.


BJP is detected in two ways:

• as an abnormal band found on EPP (electrophoresis) of concentrated urine

• as a kappa or lambda arc on IMF (immuno-fixation) of concentrated urine

Benign paraprotein see Immunoglobulins, IgA, IgG, IgM

Beta carotene see Carotene

Beta hCG see hCG (human chorionic gonadotrophin)

Beta-hydroxybutyrate

specimen: serum ref. range: 0 - 200 µmol/L

Beta-hydroxybutyrate is the test of choice when looking for ketosis in Type I diabetics because of its greater sensitivity than the more commonly (and easily) performed tests for "ketones", including dipsticks, which detect mainly aceto-acetic acid.


Beta 2 microglobulin specimen: serum

ref. range: <2.4 mg/L

ß2 microglobulin is elevated in autoimmune conditions where there is lymphocyte activation or destruction.

• multiple myeloma � used for monitoring and prognosis

• HIV � levels above 4.0 g/L are more likely to progress to AIDS

• autoimmune disease

• viral infections

• lymphoid neoplasms

• renal impairment

Bicarbonate specimen: serumref. range: <2 yrs 18 – 28 mmol/L

>2 yrs 22 - 32 "

Also known as total CO2, this is a crude acid-base measure. In metabolic acidosis, bicarbonate is reduced, e.g. in diabetic ketoacidosis. In metabolic alkalosis, it is increased � as in pyloric stenosis or the compensated respiratory acidosis of chronic obstructive airways disease.


Bile pigments in urine

specimen: random urine

This old test was used in the diagnosis of liver disorders in the first half of this century before liver enzyme assays were developed. Bilirubin is found in the dark urine of obstructive jaundice and later in the course of hepatitis. Urobilinogen is found in early hepatitis. It is colourless but darkens on standing. Bile pigments are included in the routine strip used in urinalysis. Positive results are an indication for measuring s. bilirubin and liver enzymes.

Bilharzia see Schistosomiasis

Biliary calculi see Gallstones


Bilirubin, conjugated (direct) and unconjugated (indirect) fractions

total bilirubin = conjugated + unconjugated

specimen: serum

ref. range: conjugated bilirubin is about 10% of total but precision is not good below a total of 50 µmol/L and at low levels 20% conjugated or even 30% may be normal.

Bilirubin fractions are used in two main situations:

• Persistent neonatal jaundice A conjugated bilirubin above 20-30 µmol/L at age 3 weeks requires consideration of biliary atresia/neonatal hepatitis.

see Bilirubin, total

• Isolated hyperbilirubinaemia

In Gilbert's syndrome (qv) and haemolysis, unconjugated bilirubin is the predominant fraction.

Dubin-Johnson and Rotor's Syndromes are benign, inherited, conjugated hyperbilirubinaemias.

see also Gilbert's syndrome


Bilirubin, total specimen: serum

A. Hyperbilirubinaemia in children and adults

ref. range: children and adults 5-20 µmol/L

1. Hyperbilirubinaemia with raised enzymes

see Liver enzymes

2. Hyperbiliruinaemia with normal enzymes

• Disorders of hepatic excretion � Gilbert's syndrome (qv), a common incidental finding,

is an unconjugated hyperbilirubinaemia � Dubin Johnson and Rotor syndromes, much less

common but also found incidentally, are conjugated hyperbilirubinaemias

� Crigler-Najjar syndrome is a rare severe unconjugated hyperbilirubinaemia.

• Haemolytic anaemias

� uncommon but important. Check blood count, film, reticulocytes, haptoglobins

• Other

� thyroid disease, iron overload, drug reaction, resolving hepatitis

B. Hyperbilirubinaemia in neonates – neonatal jaundice

specimen: serum, usually micro-collects which give more variable results than a venous specimen

ref. ranges:


Age µmol/Lcord blood 15-501-2 days 30-1503-7 days 50-2001-2 wks 10-1003-4 wks 5-50>1 mth 5-20

These are a rough guide to indicate levels that are likely to be comfortably within healthy limits for most neonates. Acceptable limits are lower for premature babies.

The problem with neonatal bilirubins is that many healthy, thriving babies have levels higher than the above because of two common benign conditions; physiological jaundice and the jaundice of breast-feeding.

Diagnosis of these benign conditions relies on exclusion of serious pathologies.


1. Benign Jaundice

Physiological jaundice

This is due to breakdown of foetal red cells, "immaturity" of the liver's glucuronyl transferase system and increased bilirubin resorption from bowel meconium in infants as maturation is completed during the first days and weeks of life.

The bilirubin reaches a peak in 5 days (sometimes as high as 300 µmol/L) and in bottle-fed infants disappears in 2 weeks.

Jaundice of breast-feeding

This condition, an extension of and inseparable from physiological jaundice, is due to the presence of maternal hormone in breast milk inhibiting the maturation of glucuronyl transferase.

Bilirubins can stay high for a long time. In about 2-5%, levels reach 250-350 µmol/L by the 3rd week, remain high for 3-4 weeks, falling to normal over another 1-3 months.

Despite being yellow, the infant thrives, feeds and grows. Changing to bottle-feeding results in a prompt and sustained fall in bilirubin levels and cessation of breast-feeding for 24-48 hours, with bilirubins before and after, can be used as a diagnostic test whilst maintaining lactation by manual expression.

2. Pathological jaundice

� Haemolytic disease of the newborn – Rhesus or ABO

incompatibility

Rhesus incompatibility The most severe forms of this previously dreaded disease were due to rhesus incompatibility between mother, (Rh -ve and with anti-Rh antibodies) and baby (Rh +ve). The Rhesus system was first described in 1940. Before that time, and until modern methods of prevention and treatment were developed, these babies were born


dead or anaemic with jaundice at birth increasing rapidly in the first days of life to cause long-term brain damage in the form of kernicterus. In the late 20th century, kernicterus has almost entirely disappeared but the fear of it lingers on. Haemolytic disease is caused by anti -Rh antibodies in an Rh -ve mother who has been sensitised during a previous pregnancy with an Rh +ve baby whose red cells have spilled into the maternal circulation at the time of placental separation.

Over the past 40 years this sensitisation process has been prevented by injecting the mother at delivery with enough anti-Rh immune globulin to render the foetal cells non-antigenic.

Sensitisation of the mother by an incompatible blood transfusion, unavoidable before 1940, is now an exceptionally rare event. Despite the success of preventive measures in most patients, haemolytic disease will still occasionally be found. The at-risk mother is Rh-ve and will have red cell autoantibodies when screened ante-natally,

Haemolytic disease in the at-risk infant, is diagnosed by examining cord blood at birth looking for: � Rh+ve infant � +ve Coombs test � hyperbilirubinaemia using this table as a guide:

µmol/Lfull term premature

normal <50 <25uncertain 50-125 25-80affected >125 >80

ABO incompatibility and other blood groups


This is more common but rarely severe enough to require exchange transfusion. The at-risk situation is found in 20% of pregnancies. Usually the mother is Group O and the infant Group A or B. Prior sensitisation is not required and haemolysis can occur in the first pregnancy.

Maternal antibody tests are of no use and often the direct Coombs test on cord blood is negative. Other blood groups include Kell (K), Duffy (Fya, Fyb) and Kidd (Jka, Jkb). For these incompatibilities, maternal antibodies will be present and the direct Coombs on cord blood positive.

• Neonatal bacterial infections Septicaemia is life-threatening and the infant is obviously unwell. Urinary tract infections are more easily overlooked, the infant being less obviously unwell to begin with.

• Hypothyroidism, cystic fibrosis and galactosaemia Tested on all neonates by way of the Guthrie Card blood spots � see Neonatal screening

• G-6-PD deficiency (qv) The vitamin K given routinely to neonates elevates bilirubin in G-6-PD hetero- and homozygotes. On rare occasions homozygous infants (usually males of SE Asian or Mediterranean origin) develop a severe haemolytic process in the neonatal period, especially if exposed to certain drugs.

• Biliary atresia and neonatal hepatitis The infant is often clinically well during the first few weeks but thereafter there is an increasing obstructive jaundice shown by rising


total bilirubin, a raised level of conjugated bilirubin, pale faeces and dark urine.

When and how often should bilirubins be measured?

As always, clinical judgement and experience are more important than rigid guide-lines.

A healthy term baby, growing and feeding well, without visible jaundice, does not need to have its bilirubin measured.

Premature babies need to be watched more carefully than full-term babies, particularly during the first 3-5 days.

Jaundice in the first 24 hours of life is not benign.

If the jaundiced baby is unwell, the underlying cause must be identified urgently.

If bilirubin levels continue rising after the first week or so, a cause should be sought.

How accurate is the test?

The short answer to this is "not very". At a level of 325, repeated tests on the same baby will show results varying between 300 and 350 which is the difference between referring to hospital for treatment under lights or leaving at home. Reasons for this variance are:

• problems with specimen collection. An experienced blood-collector obtaining a free flow of blood will get better results than an inexperienced person obtaining a scanty, haemolysed specimen. Haemolysis may give a result which is falsely low by up to 30-50 µmol/L.


• different laboratories use different methods

• even at best, methods have a variance of ± 7%

• the baby's bilirubin level varies throughout the day, depending on when it was last given water or milk and other variables.

What levels require treatment?

The treatment of pathological jaundice will depend on the underlying cause.

Once it has been decided the jaundice is benign, the baby is treated under lights if the bilirubin exceeds cut-off limits, usually 350 µmol/L in a full-term baby more than 3 days old. The threshold may be lower in premature babies and where the bilirubin is rising rapidly e.g. >250 @ 48 hrs.

For reasons given above, a baby with a result of 350 will sometimes be referred to hospital only to be sent back home because its in-hospital result is 320.

Levels above 400, sometimes found in infants who have escaped observation, always require urgent and immediate referral.

Biological variation see Variation

Biopsy specimens for culture

Send in sterile container with sterile saline and label clearly "for culture".


BJP see Bence Jones protein (BJP)

Blastocystis hominis

A protozoan parasite whose status as a cause of diarrhoea is still unresolved. It can be observed in the stool of asymptomatic people. Metronidazole, 400-800mg 8-hourly for 10 days, may be effective treatment.

Bleeding disorders see Coagulation screen

Bleeding time ref. range: up to 8 minutes

The test is performed as part of the standard coagulation screen.


In practice it is a measure of platelet function though when the platelet count is less than 30-50 x 109/L the bleeding time may be prolonged due to the reduced numbers of platelets.

The test is performed using a template to make a standard incision in the forearm. The time taken for bleeding to stop is a measure of platelet plug formation. The test is operator dependent and sensitive to technical variables.

It is a useful test in the diagnosis of inherited minimal bleeding disorders associated with a platelet function defect such as von Willebrand's disease. Other congenital causes of a long bleeding time include rare platelet aggregation abnormalities (Glanzmann's thrombasthenia) or storage pool defects. It is often prolonged in patients on aspirin therapy and in chronic renal failure. Acquired platelet dysfunction also occurs in immune thrombocytopenia (ITP) where the bleeding time is prolonged more than predicted for the reduced platelet count, in myeloproliferative disorders (essential thrombocythaemia), in paraproteinaemias (MGUS, myeloma) and sometimes in association with viral illness. The bleeding time is a poor predictor of the risk of surgical bleeding.

Blood collection tubes see Tubes for blood collects

Blood count specimen: whole blood (EDTA)

ref. range:

• red cells


Age Hb g/L PCV MCV fl MCH pgCord Blood 136 - 196 0.40 - 0.60 100 - 120 33 - 411—4 days 165 - 215 0.50 - 0.70 107 - 128 33 - 415—14 days 150 - 200 0.41 - 0.65 93 - 130 32 - 402—5 weeks 110 - 185 0.31 - 0.54 93 - 130 31 - 405—7 weeks 105 - 135 0.30 - 0.43 92 - 120 30 - 397—12 weeks 100 - 125 0.28 - 0.37 80 - 105 28 - 353—12 months 110 - 140 0.30 - 0.40 66 - 90 23 - 311—3 years 110 - 143 0.30 - 0.44 66 - 90 23 - 313—5 years 110 - 143 0.30 - 0.44 74 - 90 23 - 315—12 years 115 - 152 0.33 - 0.47 74 - 90 23 - 31

Females 13—15 115 - 160 0.35 - 0.47 78 - 94 25 - 34Males 13—15 yrs 116 - 165 0.37 - 0.48 78 - 92 25 - 34Females >15 yrs 115 - 160 0.35 - 0.47 80 - 98 25 - 34Males >15 yrs 130 - 175 0.38 - 0.52 80 - 98 25 - 34Antenatals 100 - 150 0.31 - 0.47 80 - 98 25 - 34

• white cells

Age WBC b/L Band. Neut. Seg. Neut. Lymphs Baso. Eos. Mono.0—7 days 10.0-25.0 0-0.6 2.0-13.0 2.0-8.5 0-0.2 0-2.0 0.3-2.51 wk—2yrs 5.0-17.0 0-0.6 0.5-7.0 2.5-12.0 0-0.2 0-1.0 0-1.02—12 yrs 4.5-14.0 0-0.6 1.2-8.3 1.5-7.3 0-0.2 0-0.5 0-0.9>12 yrs 4.0-11.0 0-0.6 2.2-7.5 1.0-3.9 0-0.2 0-0.5 0-0.9Antenatal 4.0-15.0 0-0.6 3.4-10.5 1.4-3.2 0-0.2 0-0.5 0-1.0

All cell counts are x 109/L.

Absolute counts for individual white cells give more information than the % differential counts.

Excess or deficiency of each cell type is described under individual alphabetic entries.


• platelets

Age yrs Range

0 - 12>12 female male

150 500 10

150 450 10

150 400 10

9

9

9

−

−

−

x L

x L

x L

/

/

/

see also Thrombocytopenia

Thrombocytosis

Blood culture

Bacteraemia is usually found in life-threatening illnesses which need investigation in hospital rather than at home. Nevertheless there are a few patients with low-grade febrile illnesses due to infections that shed bacteria into the blood stream but without causing overwhelming sepsis. These are found particularly in patients with cardiac valvular disease or prostheses in the heart or elsewhere. We have at times grown pneumococci, Listeria, Salmonella typhi. Almost any organism can cause bacteraemia given the right circumstances.

Blood cultures should always be considered before starting antimicrobial therapy for an undifferentiated febrile illness in a patient with a prosthetic heart valve.

Blood culture collection protocols vary from one laboratory to another. For adults two sets of adequately filled bottles, depending on clinical situation, will isolate the organism in >95% of bacteraemias. In this laboratory two sets are drawn with each collect, an aerobic and an anaerobic bottle from each arm. Standard aseptic technique must be rigidly adhered to if contamination by skin flora is to be avoided.


We use an automated detection system which allows prompt reporting of positive cultures: 60% and 90% of all positives have growth detected within 24 and 48 hours respectively. Slow-growing or antibiotic-damaged bacteria may take up to 7 days.

Blood film examination

Blood films are not routinely examined unless one or more of the blood count parameters is shown to be abnormal by the electronic cell counting analyser. In practice this means that films from 20% of blood counts are checked. The film report describes the morphological appearance of red cells, white cells and platelets. Where appropriate, the film comment will suggest a diagnosis and recommend follow-up. A blood film examination will always be performed if specifically requested even if the CBC (complete blood count) parameters are normal.

Blood gases & pH specimen: 3ml arterial blood in heparinised syringe transported on ice. ref. ranges: In Auckland and world wide, two sets of units are in use, traditional (mm Hg) and SI (kPa).

Conversion factor, 1 kPa = 7.6 mm Hg


Traditional units SI units

pH 7.36-7.44 35-45 nmol/L35-45mm Hg 4.6-6.0 kPa80-100mm Hg 10.6-13.3 kPa

HCO3- 20-28 mmol/L 20-28 mmol/Lbase excess -2 to +2 meq/L -2 to +2 mmol/L

95-100% 0.95-1.00

metabolic alkalosis = base excess >2 mmol/Lmetabolic acidosis = base excess <-2 mmol/L

O saturation2

pCO2pO 2

Blood grouping

specimen: 1 EDTA (preferred) or 1 plain tube

ABO and Rh (D) phenotype are done routinely. The frequencies of the four main groups in the ABO system and their naturally occurring antibodies are:

ABO Group Genotype Frequency Naturally occurring(%) antibodies

O OO 46 anti A,anti BA AA/AO 40 anti BB BB/BO 9 anti AAB AB 5 none

see also Crossmatch Cord blood testing

Blood in faeces


see Faeces for occult blood: occult blood

Blood in urine see Haematuria

Blood volume

Blood volume = plasma volume + red cell mass

Blood volume is measured when investigating polycythaemia (raised Hb concentration) which may be:

• relative, due to reduced plasma volume

• absolute, due to increased red cell mass

see Polycythaemia

BMI, (body mass index)

2=)metresinheight(

kginweightBMI


ref. ranges: 20-26 healthy weight range(kg/m²) 26-30 overweight

>30 obese18-20 underweight<18 very underweight

The BMI, by adjusting weight according to height, provides a useful assessment of nutritional status.

Body mass index see BMI, (body mass index)

Bone marrow

By consultation with a haematologist.

Bone marrow trephine is performed routinely together with bone marrow cytology (aspirate) and clot section. Chromosomes and cell marker analysis will be performed whenever appropriate.

Bone marrow chromosome analysis

Chromosome analysis is commonly done in the leukaemias, myelodysplastic disorders, and some lymphomas to help with classification, treatment and prognosis.


Bone marrow transplantation (BMT)

Bone marrow transplantation is being used more often. Allogeneic BMT from a matched sibling donor is still a risky procedure with mortality up to 30% primarily from graft versus host disease and infection. Autologous BMT, where the patients are their own donor, has a much lower mortality risk. Stem cells, collected from peripheral blood, are increasingly used in place of conventional autologous transplantation. They are associated with rapid engraftment and reduced hospital stay and cost. Autologous transplantation is also used in the treatment of solid tumours. Longer term complications of BMT include infertility, secondary neoplasms and endocrine dysfunction.

Bone turnover markers

When bone is resorbed, collagen cross-links are released as part of the break-down process and excreted in urine where they provide a measure of bone turnover rate in conditions such as Paget's disease, thyrotoxicosis, bone cancer, renal bone disease and hyperparathyroidism. Tests include:

� N-Telopeptide � deoxypyridinoline (DPD, Pyrilinks D) � hydroxyproline � no longer used

Serum alkaline phosphatase (ALP) and urine calcium excretion, though less specific, may also give a useful measure of bone turnover and the effectiveness of therapy.

see also N-telopeptide

Bordetella pertussis


This organism is the cause of whooping cough. Despite vaccination, the disease remains endemic in New Zealand with outbreaks at about 4-yearly intervals.

Diagnosis is by growth of the organism from a swab. A fine wire nasopharyngeal swab is passed through a nostril to reach the nasopharynx and left in place there for a few seconds. If one nostril is blocked by a turbinate or deviated septum, use the other. The swab is placed in routine transport medium for delivery to the laboratory. Delay in transport of the specimen will decrease the chances of isolation.

Adults with a chronic cough may have chronic pertussis infection which can be detected by measuring serum antibodies.

Erythromycin may reduce the duration of the disease if administered early and will reduce infectivity. A fourteen day course of erythromycin is also recommended for household and other close contacts.

Borrelia Borrelia recurrentis, a spirochete transmitted by ticks or lice, causes relapsing fever. B. burgdorferi causes Lyme disease. Neither disease is endemic in New Zealand but they may occasionally be found in travellers. Tests for antibodies against B. burgdorferi are available locally.

Branhamella catarrhalis see Moraxella catarrhalis


Breast aspirate cytology see Fine needle aspirate (FNA)

Breast tumour hormone receptors specimen: breast tissue fixed in formalin as for histology.

More than half of all breast cancers have oestrogen receptors indicating the need for endocrine therapy. They have a better prognosis than receptor negative tumours. The test uses an immunoperoxidase labelled antibody applied directly to tissue sections.

Breath test see Helicobacter pylori

Bromsulphthalein (BSP) test

no longer done

Bronchial brushings or washings

Cytology Smears are made from brushes and fixed in Cytofix immediately. Washings are submitted to the laboratory as soon as possible for cytocentrifugation.


Microbiology Collect washings into sterile containers. Please indicate special requests such as culture for TB or fungi.

Bronchitis, acute or chronic

Acute bronchitis is often a viral disease and sputum evaluation is seldom useful.

In chronic bronchitis the important pathogens are Strep. pneumoniae and Haemophilus influenzae, both usually susceptible to doxycycline, cotrimoxazole, amoxycillin-clavulanate and cefaclor. 10% of H. influenzae are resistant to amoxycillin.

Brucella antibodies specimen: serum

Brucellae are gram-negative bacilli infecting domestic animals, particularly cattle and pigs. Human infection occurs in farmers and meat-workers as an occupational hazard or by ingestion of contaminated milk products.

Over the past 30 years, brucellosis has been virtually eliminated from New Zealand cattle and human brucellosis, when found here, will almost invariably have been contracted abroad, including the Pacific Islands.

Agglutination and Coombs antibody tests detect both IgM and IgG antibodies. Results may be negative in the early stages of acute disease and sometimes antibodies are not detected at any stage. Seroconversion, however, or a >4-fold increase in antibody titre, strongly suggests active infection.


Distinguishing previous resolved infection from chronic continuing infection is impossible using antibody tests alone.

BSP (bromsulphthalein test)

no longer done

Buccal smears

This test for sex chromatin (the 2nd X chromosome in females) has been replaced by karyotype analysis.

see Cytogenetics

Bulimia see Anorexia nervosa and bulimia

Butyrate see Beta-hydroxybutyrate


C

C1 (esterase) inhibitor see Complement, C1 inhibitor (C1 INH)

C3 see Complement fractions C3 and C4

C4 see Complement fractions C3 and C4

CA 15-3 specimen: serum

ref. range: <30 U/ml

Sometimes used for monitoring established breast malignancy.


Elevations are found in other benign and malignant conditions.



70 - 80% sensitive in late stage pancreatic carcinoma. May be elevated in other gastrointestinal malignancies.


ref. range: <4.6 u/ml

Used for monitoring gastrointestinal (especially stomach) malignancies, and mucinous ovarian malignancies where it is more often elevated than Ca 125.

CA 125 specimen: serum


Mainly used for monitoring treatment and progress in established ovarian cancer.

Values >65 are consistent with ovarian malignancy in a patient with an ovarian mass.

Elevated levels may be found in other malignancies, or occasionally other non-malignant conditions including endometriosis, PID (pelvic inflammatory disease), cirrhosis, renal failure and pregnancy.


Cadmium specimen: whole blood (EDTA)

ref. range:

nmol/L

non-smokers < 36smokers < 90potentially lethal > 270

Used where toxicity is a possibility in workers involved with cadmium in industry.

Eating contaminated shellfish may raise levels. If in doubt, repeat after two weeks abstention from seafood.

Caeruloplasmin see Ceruloplasmin (copper oxidase)

Calciferol see Vitamin D

Calcitonin specimen: plasma (EDTA) ref. ranges: female <17 pg/ml male <26 pg/ml


Calcitonin is a hypocalcaemic hormone produced naturally by the thyroid. There are no clinical excess or deficiency states.

Calcitonin's clinical use is as a marker for medullary thyroid carcinoma either as an isolated tumour or as part of MEN (qv) multiple endocrine neoplasia, type II, along with phaeochromocytoma and parathyroid tumours.

Calcium (total) specimen: serum

ref. range:

0 - 1 mth 1.90 - 2.851 mth - 12 yrs 2.20 - 2.70>12 yrs 2.10 - 2.55

A protein correction is routinely applied:

)albumin-40(02.0+Caobserved=Caadjusted ++++

Hypercalcaemia The two most important causes are:

• Hyperparathyroidism due to parathyroid adenoma

The parathyroid hormone (PTH) level is increased.

Severe 1° hyperparathyroidism with calcium levels above 3.00 mmol/L will require surgical removal of the parathyroid adenoma.


Minor asymptomatic degrees are common, however, and are generally managed with observation rather than surgery, particularly when s. calcium <2.75. These "benign" hypercalcaemias are much more common in the elderly.

• Malignant disease, particularly metastatic tumour in bone, multiple myeloma or cancer of lung, breast or urinary tract, producing an ectopic PTH-like hormone, PTHrP (PTH related Peptide).

Other causes of hypercalcaemia include: � drugs � vitamin D thiazides lithium antacids � thyrotoxicosis � sarcoidosis � familial hypocalciuric hypercalcaemia � renal transplantation � Paget's disease with immobilisation

Hypocalcaemia � chronic renal failure � vitamin D deficiency � hypoparathyroidism (usually post-thyroidectomy) � drugs � anticonvulsants � frusemide � biphosphonates � oral phosphate � malabsorption � pancreatitis � hypomagnesaemia


Calcium (ionised) specimen: serum

ref. range: 1.15�1.35 mmol/L

About half of total serum calcium is bound to albumin and inactive. The other, ionised half is the physiologically active fraction. Ionised calcium levels are raised in sera with an acid pH and lowered when alkaline.

For most clinical purposes, adjusted total calcium is adequate but in severe protein abnormalities, including malignant paraproteinaemias and chronic renal failure, ionised calcium may be more useful.

Calcium, urine specimen: 24-hr urine collected into HCl

ref. range: 2.5�7.5 mmol/day

Some patients with recurrent renal calculi have a high urinary calcium output � idiopathic hypercalciuria. Serum calcium must be checked to exclude hypercalcaemia.

Calculi, biliary see Gallstones

Calculi, renal


see Renal calculi

Campylobacter jejuni/coli

Infections with Campylobacter jejuni or Campylobacter coli cause 60% of bacterial diarrhoea in the community. These organisms cause an acute enterocolitis which can be associated with intense abdominal pain. The average incubation period is 3 days; most patients recover within a week. Antibiotic treatment is usually not required but for severe infections erythromycin is effective. Treatment with quinolones is not recommended because resistance to them emerges commonly and rapidly. Untreated patients may excrete Campylobacter in their faeces for 2�3 weeks but transmissability is low and it is not usual to put restrictions on otherwise healthy food handlers who are excreting the organism.

Campylobacter pylori see Helicobacter pylori

Candida Candida albicans, the principal pathogenic yeast in humans, is a member of the normal flora of the gut, respiratory tract and vagina. It can gain dominance under certain conditions such as diabetes, antibiotic use and suppression of the immune system. Other species of Candida which are occasionally isolated cause the same type of infection as C. albicans. For most, the treatment is the same as for C. albicans.

The main sites and types of infection are:


Vulvo-vaginitis Predisposing factors are antibiotics, diabetes, pregnancy and progestagens. Some individuals suffer from recurrent thrush for no detectable reason. A random glucose should be checked to exclude diabetes.

specimen: vaginal swab in transport medium

Skin Infection occurs in warm moist areas such as the groin, perianal region, axillae, the breasts or in interdigital webs. It is often seen in those who frequently immerse their hands in warm water, such as dishwashers.

specimen: skin swab in transport medium

Nails Candida can cause a painful red swelling of the nail fold resembling pyogenic paronychia, This may progress to nail involvement (onychomycosis).

specimen: skin swab in transport medium

nail scrapings for mycology will grow Candida if present

Mouth Infections are found mainly in infants and show up as white adherent patches. Laboratory identification is not usually necessary but a swab will grow the yeast.

Systemic candidiasis Found in immunocompromised patients or in association with prostheses.

Cannabinoids specimen: random urine (no preservative)


Cannabis is rapidly absorbed into fat depots with cannabinoids remaining detectable in the urine for up to 1 - 2 weeks after a single exposure. In chronic users, cannabinoids remain detectable for up to 6 weeks after cessation.

Cannabis see Cannabinoids

Carbamates

Carbamates are insecticides similar in their mode of action to organophosphates (qv) but with a shorter duration of effect and lower order of toxicity.

see Cholinesterase

Carbamazepine (Tegretol) see Anticonvulsants

Carbon dioxide (CO2) see Blood gases & pH Bicarbonate


Carbon monoxide see Carboxyhaemoglobin

Carboxyhaemoglobin

specimen: whole blood (heparin)

ref. range:

COHb as % of total Hb

non-smokers 0.5 - 1.5smokers 2.0 - 9.0toxic levels: mild symptoms 15 - 20 moderate symptoms 20 - 40 severe symptoms 40 - 60 often fatal >60

The affinity of CO for Hb is 200 x that of oxygen.

CO toxicity is mainly due to deliberate or accidental exposure to car exhaust fumes.

Levels fall about 15% per hour in air after removal of the CO source. Oxygen treatment, particularly hyperbaric, accelerates clearance of CO.


Carcinoembryonic antigen (CEA) specimen: serum ref. range: <3.0 µg/L non-smokers <5.0 µg/L smokers

CEA is elevated in some malignancies, particularly of the bowel. It is used for monitoring treatment of tumours and for detecting recurrence but because of its low specificity it is not used diagnostically in patients without known malignancy. Non-malignant elevations occur particularly in disorders of liver, blood and lungs but are usually below 20 µg/L.

see also Tumour markers

Carcinoid syndrome see HIAA (5-hydroxy indole acetic acid)

Cardiac enzymes see Myocardial enzymes


Cardiolipin antibodies (aCL) specimen: serum ref. range: IgG aCL <5 GPL IgM aCL <5 MPL

High levels of the IgG antibody are found in:-

• antiphospholipid syndrome (qv)

• SLE

• other autoimmune disorders

• in some healthy people

A first indication of aCL may be a "false positive" VDRL or RPR test during routine antenatal screening.

Low titre antibodies may be transient and are of uncertain significance.

see also Antiphospholipid antibody syndrome (APS)

Cardiovascular disease (CVD) risk assessment In cardiovascular disease until relatively recently, each risk factor (e.g. serum cholesterol) has been treated in isolation but the preferred option now is to present all risk factors integrated into a single figure � the 5-year absolute cardiovascular risk � and select treatment options according to the level of risk.

A CVD event is any of the following:

• Myocardial infarct (MI), angina, cardiac death, congestive heart failure (CHF)


• stroke, transient ischaemic attack (TIA) • claudication

A 5-year absolute risk of say 10% means that of 100 patients with a similar risk profile, 10 will have a CVD event in the next 5 years.

Or, put another way, a patient with a 10% absolute risk has a 1 in 10 chance of a CVD event within 5 years.

Absolute risk is automatically assessed as very high (>20%) if the patient has any of the following:

� known CVD (MI, angina, CHF, stroke, TIA)

� diabetic nephropathy

� known familial dyslipidaemia (see lipid disorders)

Otherwise risk is calculated using the tables overleaf; or using the appropriate programme in your computer; or by having the laboratory add it your patient's lipid profile in which case you will have to add information on the laboratory request form

� diabetes yes/no

� systolic BP

� smoker yes/no

� personal history CVD (automatically >20%)

Age is a potent risk factor and above 70, risk is always high.

If total cholesterol is >8 mmol/L or total/HDL ratio is >8, the patient is always classified as at least high risk (i.e. >15%).


see also Cholesterol Lipid disorders

MENNo diabetes Diabetes

nonsmoker smoker nonsmoker smokerratio of total cholesterol:HDL ratio of total cholesterol:HDL4 5 6 7 8 4 5 6 7 8 4 5 6 7 8 4 5 6 7 8

180/105 180/105160/95 AGE 160/95140/85 70 140/85120/75 120/75

180/105 180/105

160/95 AGE 160/95140/85 60 140/85120/75 120/75

180/105 180/105

160/95 AGE 160/95140/85 50 140/85120/75 120/75

180/105 180/105

160/95 AGE 160/95140/85 40 140/85120/75 120/75

4 5 6 7 8 4 5 6 7 8 4 5 6 7 8 4 5 6 7 8ratio of total cholesterol:HDL ratio of total cholesterol:HDL

Bloo

d Pr

essu

re

Blood Pressure

To use tables:

— identify table relating to person's gender, diabetic status, smoking status, age. � within the selected table, find the cell nearest to the person's blood pressure

and ratio of total cholesterol : HDL.

� use cell shading from key on opposite page to identify risk level.


WOMENNo diabetes Diabetes

nonsmoker smoker nonsmoker smokerratio of total cholesterol:HDL ratio of total cholesterol:HDL4 5 6 7 8 4 5 6 7 8 4 5 6 7 8 4 5 6 7 8

180/105 180/105160/95 AGE 160/95140/85 70 140/85120/75 120/75

180/105 180/105

160/95 AGE 160/95140/85 60 140/85120/75 120/75

180/105 180/105

160/95 AGE 160/95140/85 50 140/85120/75 120/75

180/105 180/105

160/95 AGE 160/95140/85 40 140/85120/75 120/75

4 5 6 7 8 4 5 6 7 8 4 5 6 7 8 4 5 6 7 8ratio of total cholesterol:HDL ratio of total cholesterol:HDL

Bloo

d Pr

essu

re Blood Pressure

high >30%

25-30%

20-25%

15-20%

10-15%

5-10%

2.5-5%

low <2.5%

Risk Level:Percent chance ofa cardiovascularevent in 5 years


Carotene specimen: serum, protected from light to prevent photo-decomposition.

ref. range: 0.2�1.5 µmol/L

Carotene levels are used in the diagnosis of carotenaemia, an orange-yellow coloration of the skin (but not conjunctivae) that can look like jaundice. The usual cause is a high intake of vitamin A precursors in carrot or other coloured fruit or vegetable juice but some systemic illnesses, including hypothyroidism, diabetes, liver and renal disease, can cause carotenaemia. Because carotene is lipid-soluble, hyperlipidaemias can give elevated levels. Low values have been used as an indicator of malabsorption but specificity and sensitivity are poor.

Casts in urine see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections)

Catecholamines

specimen: 24�hr urine with 20ml 6M HCl as preservative. Specimens with a pH above 3 (indicating insufficient or no acid) cannot be

analysed. In children, a spot urine can be used, delivered to the laboratory as soon as

possible for adjustment of pH.


ref. range:

Adult µmol/L/daynoradrenalin 0.08 - 0.47adrenalin 0.00 - 0.11dopamine 0.4 - 3.0

Different ranges are used for children.

Indications Phaeochromocytoma 25% of the population have hypertension but only a fraction of these can or should be screened for a phaeochromocytoma. Particular indications are:

• symptoms, including sweating attacks, severe headaches, palpitations, nervousness, chest pain; flushing attacks are very uncommon.

• episodic hypertension (not always present)

• moderate or severe hypertension in pregnancy or in young people.

• adrenal mass

Neuroblastoma These usually present as an abdominal mass in children under the age of 5.

Number of specimens When clinical suspicion is low, a single normal result is sufficient but when suspicion is high, up to three specimens should be tested, preferably collected during or just after symptoms.

Interpretation The typical phaeochromocytoma gives a noradrenaline level of 1.0 � 2.0 µmol/day. Occasionally the adrenaline level is elevated but usually it and the dopamine are near normal. In malignant phaeochromocytomas (10% of the total), dopamine tends to be elevated as well as noradrenaline.

The typical neuroblastoma shows a huge increase in dopamine.


Non-tumour elevations can be caused by anxiety, stress and exercise, particularly in the case of dopamine where elevations can be up to twice the upper limit. Small, isolated elevations of dopamine can usually be ignored.

Essential hypertension can be associated with a minor increase in noradrenaline, usually less than twice the upper limit.

Medication Noradrenaline is increased by amphetamines, alpha- and beta-blockers, vasodilators, theophylline, phenothiazines and tricyclic antidepressants.

Noradrenaline is decreased by clonidine, methyldopa, and bromocriptine.

Dopamine is massively increased by levodopa.

Cat scratch disease Specimens:

1. culture (slow - up to 28 days) � blood (EDTA). � tissue or FNA in sterile container 2. serology � paired sera, 2-3 weeks apart 3. histology, cytology � formalin-fixed tissue, usually lymph node, for histology � FNA material for cytology


Cat scratch disease (CSD) is a self-limiting febrile illness with localised tender lymphadenopathy caused by Bartonella (previously Rochalimaea) henselae which is transmitted when a bacteraemic cat or kitten bites or scratches a human. In the United States, where one third of households have a cat, the annual incidence of CSD is 100 cases/million population, 80% of them in children.

Although CSD was first reported in 1931, it is only recently that B. henselae, a fastidious slow-growing, gram-negative rod, was identified as the pathogen responsible. A study of cats in Auckland found 17% with B. henselae bacteraemia. Fleas transfer the organism from cat to cat and flea control is a useful preventive measure.

Severe systemic illness can occur in immuno-compromised individuals.

Treatment. Pain relief may be required. Steroids are generally ineffective. There are no controlled trials to help choose an antibiotic but for those with prolonged fever and/or severe lymphadenitis, erythromycin, doxycycline, clarithromycin, ciprofloxacin, aminoglycosides and sulphamethoxazole/trimethoprim have been used. Therapy should be discussed with an infectious disease specialist.

CBC (complete blood count) see Blood count

CD4 T-lymphocytes

specimen: whole bloods

lymphocytes are stable for only 6 hours in EDTA but in ACD tubes they are stable for several days.


ref. range: adult 500-1650 cells/µl

The CD4 count (or CD4/CD8 ratio) is used to monitor the T-lymphocyte status in HIV patients and the immune defect induced by the adenosine analogues used to treat some haematological malignancies. As counts fall below 200/cmm, opportunistic infections become increasingly common.

CD59

An absence of CD59 activity on the cell surface of red cells characterises paroxysmal nocturnal haemoglobinuria (PNH).

see PNH

CEA see Carcinoembryonic antigen (CEA)

Celiac disease see Coeliac disease (gluten sensitive enteropathy)

Cerebrospinal fluid see CSF (cerebrospinal fluid)


Ceruloplasmin (copper oxidase) specimen: serum

ref. range: 0.15 � 0.45 g/L

Ceruloplasmin is reduced in hepatolenticular degeneration (Wilson's disease), and Menke's kinky (steely) hair syndrome.

Oestrogens, anticonvulsants and inflammation cause elevations � ceruloplasmin is a late acute phase reactant. 95% of serum copper is carried by ceruloplasmin.

see also Copper

Cervical cytology

specimen:

The specimen is collected by a spatula, a combination of spatula and cytobrush, or a cervix broom.

The cells must be representative of the cells lining the cervix. Squamous cell cancer of the cervix, which accounts for 60-80% of invasive cancers, begins as cervical intraepithelial neoplasia at the squamocolumnar junction. It is important to sample this site to detect early changes.

The ideal sample consists almost entirely of squamous cells which line the ectocervix and a small number of endocervical glandular cells to indicate that the squamocolumnar junction has been sampled.


A. Collecting specimens:

There are two methods:

• conventional pap (papanicolaou) test • Thin Prep pap test

1. Conventional Pap test

Essentially unchanged for the last 50 years, this test has saved the lives of many women reducing mortality from cervical cancer by more than 70%.

Preparation

Write the patient�s name on the frosted end of the slide in pencil (HB is fine) and have the fixative (Cytofix or Cytospray) ready for use.

Taking the smear Using a speculum display the cervix and ensure the external os is accessible. Carefully wipe away excess mucus and inspect the cervix in good light. If the cervix looks abnormal the women should be referred for colposcopic examination regardless of the cytology report.

The specimen should be collected with either a spatula and cytobrush or a cervix broom.

Spatula and Cytobrush

The spatula specimen is collected first because of the tendency of the cytobrush to causebleeding.

The tip of the spatula is inserted into the cervical canal and carefully rotated through 360º obtaining cells from the ectocervix, transformation zone and lower endocervix. The spatula must make sustained contact with the cervix throughout the whole rotation if segments are not to be missed.


While an adequate sample is often obtained just with a spatula, the addition of a cytobrush usually ensures the presence of endocervical cells and permits good sampling of the canal if this is where the squamocolumnar junction is situated. Adenocarcinoma of the endocervix and its precursor adenocarcinoma in situ (AIS) may also be detected in asymptomatic women.

Cytobrush smear Indications for cytobrush smears are: • repeat smears on patients with abnormalities e.g. CIN (cervial intraepithelial

neoplasia), HPV (human papiloma virus).

• where the anatomy of the canal has been altered by age as in post-menopausal women or by treatment such as cone or Lletz biopsy.

• repeating a smear where previously no endocervical cells were obtained.

• abnormal bleeding


Cytobrush Method The Cytobrush is gently inserted into the endocervix canal and rotated one full turn. The contents of the brush are transferred to the labelled slide using a rolling or rotary motion along the surface of the slide. Collection of the obligatory spatula smear must precede that of the cytobrush smear.

The specimen, once smeared, needs to be fixed within 4-5 seconds to prevent fixation artefact.

Fixation Two methods are commonly used. 1. Coplin jar

This is a glass or plastic jar with slots in the side of the jar to ensure the slides stand up in the jar and do not touch their neighbours. The Coplin jar is filled with cytofix.

It is important to keep the lid on the jar as this prevents evaporation of the cytofix which should be changed every 3-4 days or every 15-20 slides.


The slides need to be immersed for at least 15 mins. Wet slides may be then placed in plastic (pink) slide mailers and sent to the laboratory.

2. Cytospray

Cytospray is available in either 100 or 200ml bottles with an environmentally friendly pump action spray. Cytospray is not the same as cytofix. Cytospray is 95% alcohol with wax added to prevent rapid evaporation of the alcohol once sprayed onto the slide.

It is important to hold the spray bottle at least 20 cm from the slide and produce a good powerful fine droplet spray. If the spray bottle is held too close to the slide or large droplets are created then the cells may be damaged and the slide rendered uninterpretable. The slide may be placed in the plastic slide mailers, sprayed and the mailer closed and sent to Diagnostic. Can the cytobrush smear go on the same slide as the spatula smear? The answer is yes, provided you take precautions to ensure there is no delay in fixation.

Here are two methods:

• �Store� the spatula in the moist environment of the posterior vaginal fornix after the spatula smear has been taken, while the cytobrush specimen is taken. Spread the smears on opposite halves of the slide in quick succession and fix immediately.

• Spread the spatula specimen on one half of the slide. Immediately cover

the other half with a layer of paper and spray the spatula smear taking care that no fixative runs under the paper or through it onto the unused half. If this happens cells will not stick to the slide and will be lost during processing. Now collect the cytobrush smear and spread it on the remaining half slide. Spray with fixative.

• Sometimes it may be necessary to use two separate slides. Collection and

fixation of the spatula smear is completed before collecting the cytobrush smear. While this doubles the screening time, for the patient�s sake we


would rather have a good sample on two slides than a less than optimal sample on one slide.

Cervix broom

• This device is used alone. • The central bristles of the broom are inserted into the endocervical canal deep

enough to allow the shorter bristles to fully contact the ectocervix. Push gently, and rotate the broom in a clockwise direction 2 to 3 times.

• Gently wipe the cell sample onto the glass slide as if one were using a

paintbrush, first n one direction then in the other direction making sure all the bristles and both sides come in contact with the slide. Repeated brushing back and forth is not recommended as this will damage the cells.

• Fix the slide immediately.

B. Thin Prep Pap test

This is a new way of processing cells taken from the cervix, utilising fluid-based specimen collection.

The sample is collected in the normal way but instead of smearing the sample on a slide, it is rinsed in a fluid containing fixative. The sample is put into a machine which filters out most of the blood and inflammatory exudate and prepares a smear with a thin even layer of cells. The smear is then screened in the normal way by a cytology screener.

The advantages of this system are:

1. Nearly all the cells collected are transferred to the sample providing a

representative homogeneous smear.

2. There are no preparation artefacts such as air drying and obscuring blood and inflammatory debris are removed.


3. Multiple slides can be prepared from one sample and part of the sample might be used for ancillary studies e.g. molecular probes for identifying Chlamydia, HPV, etc.

In clinical trials the Thin Prep Pap Test has been shown to have the following advantages

• it is more sensitive than the conventional pap test in detecting

abnormalities. • it gives better quality slides leading to a decrease in the number of

smears called unsatisfactory or less than optional. • fewer smears are reported as atypical squamous cells of uncertain

significance.

Specimen collection 1. The specimen is collected as for a conventional smear except that a plastic

spatula is used rather than a wooden one. 2. The collection device is rinsed vigorously in PreservCyt ® solution. The

cytobrush or cervix broom should be rotated at least 10 times in the solution and then discarded. The bristles of the cytobrush and cervix broom should be forced apart on the side and bottom of the collection vial.

3. The cap of the vial should be tightened so that the tongue line on the cap

passes the tongue line on the vial. 4. Record the patient's name on the vial and then place with the completed

cytologyrequest form in a biohazard bag for collection by the laboratory. This technology appears to offer an improved method of processing a cervical smear which may have a significant impact on reducing false negative Pap smears. It remains uncertain whether the additional cost of Thin Prep is justified. However, if the number of repeat smears, unnecessary procedures and number of women who develop invasive cervical cancer can be reduced using this technology, the costs of cervical cancer screening and treatment may ultimately be reduced.


B. Cervical Cytology Reports The Bethesda system reports under three headings: 1. Adequacy of specimen � whether squamous cells are scanty, adequate or abundant � whether endocervical glandular cells are present or absent � quality of fixation � presence of excessive blood or inflammatory exudate 2. Description of findings The main categories of abnormalities are: � ASCUS (abnormal squamous cells of uncertain significance) On follow-up, many examples of ASCUS will revert to

normal, some will remain ASCUS, a few will progress to more definite abnormality.

— Low-Grade Abnormality (formerly CIN 1) As with ASCUS, many low-grade abnormalities will revert

to normal. Two low-grade abnormal smears six months apart are an indication for colposcopy.

� High-Grade Abnormality (formerly CIN 2 and CIN 3) A high-grade abnormality is an indication for colposcopy

and biopsy. � HPV and other cytologically detectable infections will be

noted. HPV alone is managed as a low-grade abnormality. 3. Recommended follow-up Follow-up recommendations take account of current and past

findings. Possibilities are: � routine follow-up in three years � follow-up in six months for ASCUS or low-grade

abnormalities


� colposcopy and biopsy for high grade abnormalities or repeated low-grade lesions.

Cervical swabs

Swabs are collected from the cervical canal when testing for Neisseria or Chlamydia trachomatis � see entries under these headings.

CFT (complement fixation test)

A methodology used for detecting a wide variety of antibodies.

Chicken pox see Varicella-zoster virus (VZV)

Chilomastix mesnili

A non-pathogenic commensal flagellate found in faeces. When present it can suggest infestation with worms which may warrant treatment.


Chlamydia pneumoniae specimens:

1. antibodies - serum, preferably paired sera 2-3 weeks apart

interpretation: single specimen <1:16 negative

1:16-1:32 indeterminate>1:32 past or present infection

paired sera 4-fold or greater increase indicates current infection

2. culture � please discuss with microbiologist.Requires a nasopharyngeal swab in special medium.

C. pneumonia has recently been recognised as an important cause of atypical pneumonia, second only to Mycoplasma. Like the other Chlamydia it is an obligate intracellular bacterium. It was previously called the TWAR agent.

Spectrum of disease

Many adults have antibodies indicating that the infection is common, initial infection being typically at age 5-15 years. It can cause pneumonia, severe pharyngitis, hoarseness, fever, cervical lymphadenopathy. Infection in young adults is usually of mild to moderate severity but can be sub-clinical or, in immunocompromised patients, severe. Incubation period averages 21 days and infection can recur. Its most recent (and surprising) association is with coronary artery disease, suggested by seroepidemiologic studies and finding the organism in atheromatous plaques.

Laboratory diagnosis is typically based on serology.

Treatment for lower respiratory tract infection is erythromycin or other macrolides in children and doxycycline or macrolides in adults. 10 - 21 days may be required as prolonged or recurrent symptoms are common.


Chlamydia psittaci

specimens:1. antibodies - serum, preferably paired sera 2-3 weeks apart

interpretation: single specimen <1:16 negative

1:16-1:32 indeterminate>1:32 past or present infection

paired sera 4-fold or greater increase indicates current infection

C. psittaci is a pathogen endemic in all bird species. When a human inhales dust from fomites from infected birds, they can develop an infection which may present as an atypical pneumonia, headache, fever, rash, myalgia. Severity ranges from mild to moderate, occasionally severe.

Psittacosis is largely confined to bird-fanciers (the parrot family particularly) and poultry-handlers.

Laboratory diagnosis is based on antibody findings.

Treatment � tetracyclines or the macrolides.

Chlamydia trachomatis

In New Zealand the term "chlamydia" commonly refers to genital infections with C. trachomatis. They are widespread in the community.

Infection is diagnosed by detecting chlamydia antigen in cellular material using an ELISA method.


Specimens: female � urethral swab and cervical swab male � urethral swab or first-catch urine conjunctivitis � conjunctival swab

Each chlamydia pack has 3 swabs

� a single thin wire urethral swab � 2 larger cervical swabs

Swabs must be placed in the purple top tube provided for transport. Female specimens Use one of the large swabs to clean secretions away from the cervical os. Now insert the second large swab 1-2cm into the endocervical canal and rotate for 15-30 secs. Chlamydia are located inside cells, not secretions, hence the need to rotate the swab against the cells lining the cervical canal. Now insert the thin swab into the urethra and rotate to collect the second specimen. Sampling both cervix and urethra, only one of which may be infected, increases recovery rate by 15-20%. Vaginal swabs are of no value. Male specimens If there is a urethral discharge, swab the inside of the urethral meatus. Insert the swab 2-4cm into the urethra and rotate for 3-5 seconds to ensure adequate sampling. As an alternative, particularly when there is no discharge, collect 10-20 mls of first-catch urine, i.e. the first stream of urine, which flushes chlamydial discharge out of the urethra. The patient should not have voided for several hours before providing the first void urine. Label this urine specimen clearly "for chlamydia".


Conjunctivitis Swab the inside of the lower eye-lid using the smaller urethral swab. Remove any purulent material before collecting conjunctival epithelial cells by rubbing the dry swab over the everted palpebral conjunctiva. Other Types of Test � culture is occasionally used e.g. for medico-legal reasons � molecular methods such as LCR (ligase chain reaction) and PCR

(polymerase chain reaction) are alternatives to the ELISA methods. � antibody tests are seldom used.

When to test for chlamydia � when an STD (sexually transmitted disease) is suspected � when a cervical smear is collected � during pregnancy because infection can be passed to the infant during birth.

It is not necessary to do a test of cure following doxycycline treatment.

In pregnancy, doxycycline cannot be used. A test of cure should be done after completing a course of one of the alternative agents as these have a known failure rate.

Tests should not be performed until 3 weeks after treatment to prevent false positives due to persisting dead antigen, or false negatives due to persisting live organisms being too small in number to register positive.

Reliability of the antigen test

All results reported as positive have been confirmed using a different methodology to eliminate most false positives. The current literature gives the predictive value of a confirmed positive as >99%. As with all laboratory tests the possibility of both false positives and false negatives needs to be kept in mind when a result seems not to fit the clinical situation.


In Auckland the overall positivity for all people tested is 5%.

Treatment

Chlamydia is treated with doxycycline, 100mg 12-hourly, for 7�10 days except in pregnant women where amoxycillin, 500mg 8-hourly, or erythromycin, 500mg base 6-hourly, is used. Recently azithromycin as a 1g single dose has been approved. This is likely to become the standard treatment of genital C. trachomatis infection in New Zealand.

C. trachomatis conjunctivitis � for neonates erythromycin 50mg/kg/day divided 6-hourly for 10-14 days is recommended. In adults prolonged treatment for 3 weeks with doxycycline or erythromycin is used. Regardless of age, topical antibiotics are inadequate and are unnecessary when oral treatment is given.


Spectrum of disease:

Genital infections

• urethritis, males and females, often asymptomatic in females. 60% of non-gonococcal urethritis is due to chlamydia.

• cervicitis, usually asymptomatic

• salpingitis and pelvic inflammatory disease, an important cause of infertility

• conjunctivitis, in infants born to infected mothers or in adults who get genital secretions into an eye.

Other sub-types of C. trachomatis cause • trachoma, a chronic conjunctivitis which is a major cause of conjunctival scarring

and blindness in developing countries.

• LGV (lymphogranuloma venereum), found mainly in Africa, Asia and South America, an STD causing chronic granulomatous inguinal lymphadenopathy.

Chloride specimen: serum

ref. range: 95 � 110 mmol/L

Formerly, chloride was measured as part of the electrolyte group but it has now fallen into disuse except for a few specialised situations in renal medicine. Those who calculate anion gaps will need a chloride level.

Cholesterol Total cholesterol is made up of three fractions:


total = LDL + HDL + VLDL/IDL

Total and HDL cholesterols are measured directly in the laboratory.

VLDL/IDL is estimated from the fasting triglyceride using the formula

VLDLtriglyceride

=2 2.

LDL is calculated by subtraction using the Friedewald formula.

LDL total HDLtriglyceride

= − −2 2.

The formula is inaccurate and not used when the triglyceride is above 4.5.

see Cholesterol, HDL

Cholesterol, LDL

Cholesterol, total and total/HDL ratio

also Cardiovascular disease (CVD) risk assessment

Lipid disorders

Triglyceride

Cholesterol, HDL specimen: serum


ref. range: 1.0 - 2.5 mmol/L

Female levels are on average 0.3 mmol/L higher than male.

The current NHF (National Heart Foundation) recommended level is >1.0 which is relatively easily achieved, 80% of females being above this level and 60% of males.

HDL cholesterol is protective against atherosclerosis and a low HDL is an independent risk factor separate from LDL cholesterol.

increased by � exercise � alcohol � drugs � oestrogens � fibrates, statins, nicotinic acid � anticonvulsants decreased by � drugs � androgens, anabolic steroids, danazol, testosterone � progestins � beta blockers � thiazides � isotretinoin � antiviral agents � smoking � obesity � familial hypolipoproteinaemia � renal impairment/proteinuria

Athletes using anabolic steroids can have dramatically low HDL levels.


Cholesterol, LDL

specimen: serum, fasting (see cholesterol, total)

ref. range: NHF (National Heart Foundation) recommended ideal level <3.0 mmol/L

LDL cholesterol is calculated using the Friedewald formula � see under Cholesterol above.

It is a major risk factor for coronary artery disease.

Quantitatively it makes up about 80% of total cholesterol in a normal person and for this reason the terms total and LDL cholesterol are often used interchangeably, even though there are significant differences.

The two main determinants of LDL levels in healthy people are:

• genetic inheritance � responsible for more than half the LDL level and not modifiable except by drugs

• diet

elevated by:

• polygenic hypercholesterolaemia

• familial hyperlipoproteinaemia

• high fat diet

• diabetes

• hypothyroidism

• alcohol

• nephrotic syndrome


• drugs: glucocorticoids, beta-blockers, thiazides, danazol, androgens, isotretinon, anti-viral agents, cyclosporin

lowered by:

• ideal diet

• oestrogens

• drugs: statins, fibrates, nicotinic acid, bile resins

see also Cholesterol, total and total/HDL ratio

Lipid disorders

Cholesterol, total and total/HDL ratio

specimen: serum ref. range: NHF ideal levels � total cholesterol <5.0 � total/HDL ratio <4.5

Fasting or non-fasting?

• Total and HDL can be non-fasting.

• LDL cholesterol and triglyceride should be fasting. A point worth making is that for a person eating a healthy low fat breakfast or lunch, there will be no significant difference between fasting and non-fasting.

A reasonable approach is to make the first profile non-fasting. If levels are higher than ideal, a second fasting specimen is ordered to complete the baseline.


Observed ranges by age and gender

The graph below shows "observed" total cholesterol ranges in 80,000 unselected sera in the Auckland population 1997 - 1998. It can be seen that in the 45-70 age-group, about 70% lie above the ideal level at 5.0 mmol/L. Female and male mean levels are shown separately but the 5th and 95th percentile lines are for male and female combined.

Factors affecting total cholesterol

Because the LDL fraction makes up about 80% of total cholesterol, those factors which raise or lower LDL cholesterol (qv) will have the same effect on total cholesterol.

There are differences however:


total LDL HDLtriglyceride

= + +2 2.

It can be seen that a high triglyceride has an important effect on total levels whilst LDL is relatively unaffected by triglyceride � hence the importance of examining a full lipid profile, not just total cholesterol.

The full profile is also essential to measure HDL as an important independent risk factor and to measure triglyceride which is also being recognised as a risk factor, e.g. in women and diabetics.

Total /HDL ratio

This ratio integrates the contributions of HDL and LDL into a single figure, showing the magnification of risk when LDL is high and HDL low; and also how a high HDL can diminish the importance of a high LDL.

ratio <4.5 — ideal4.5-8.0 — low medium risk>8.0 — high risk

Variance in total cholesterol when monitoring treatment

At a level of 6.5 mmol/L the biological variance is about ± 0.5 mmol which means that changes between 6.0 and 7.0 are not necessarily significant. Serial measurements, say monthly or 3-monthly, are necessary to smooth out these random oscillations and show whether the trend is down, up or unchanged.

see also Lipid disorders


Cholinesterase specimen:

• whole blood (heparin) is preferred because it can be used for both red cell and plasma cholinesterase measurements when checking for insecticide poisoning and can be used in detecting scoline sensitivity.

• serum can, however, be used for all tests except red cell cholinesterase.

• please include clinical details.

ref. ranges: red cell cholinesterase 9 - 16 Unitsplasma or serum cholinesterase4.9 - 12.0 U/mldibucaine inhibition number 81 - 86

Indications: 1. Chronic exposure to organophosphate and carbamate anticholinesterase

sprays Organophosphates Carbamates malathion carbaryl acephate methiocarb coumaphos methomyl chlopyrifos propoxur These insecticide sprays are widely used by horticulturists.

Red cell and plasma cholinesterases should be measured before spraying commences to establish the individual's baseline reference range and at regular intervals thereafter.

If the baseline is unknown, estimations at 3-day intervals after removal from exposure will show recovery towards the baseline.

Because red cell cholinesterases are irreversibly inhibited by organophosphates (but not carbamates), levels remain low for the 4-month life


of erythrocytes. The red cell level is the preferred test for monitoring low level chronic exposure.

2. Acute poisoning

Plasma cholinesterases fall sharply when acutely exposed to organophosphastes or carbamates but recover to their previous levels within less than a week.

Measure plasma (or serum) cholinesterase

3. Scoline (suxamethonium) sensitivity

Measure serum or plasma cholinesterase and dibucaine number. Do not test within one week of scoline administration or two weeks of blood transfusion.

4. Other Cholinesterase levels are reduced in chronic liver disease, renal disease,

pregnancy/oestrogens, acute illness.

Choriocarcinoma see hCG (human chorionic gonadotrophin)

Chorionic gonadotrophin see hCG (human chorionic gonadotrophin)

Chorionic villous sampling


Prenatal diagnosis for selected inherited diseases is performed at 9-11 weeks gestation on foetal DNA extracted from chorionic villi. This is used for the antenatal detection of an increasingly wide range of severe, untreatable disorders where termination is a reasonable option to consider.

Chromium specimen: random urine with added HCl

ref. ranges : normal < 2µmol chromium/mol creatinineexposure > 4µmol chromium/mol creatinine

When the test is being done in welders, the specimen should be collected towards the end of the working week.

Chromosome analysis see Cytogenetics

Chronic fatigue syndrome

This relatively common condition (1-2 per 1000) continues to attract attention in both the lay and medical press.

We are sometimes asked by patients if there is a simple yes/no diagnostic test and so far there is none, despite occasional claims to the contrary. The diagnosis is based on the history of debilitating fatigue for at least 6 months in the absence of any clinical or laboratory evidence of identifiable organic disease.


Conditions to be excluded include endocrine disease (diabetes, thyroid) specific infections (mainly viral such as infectious mononucleosis, Coxsackie B, CMV) connective tissue disorders and neuro-muscular disease.

Chronic lymphocytic leukaemia (CLL)

Typically CLL is an indolent disorder with a median survival of 10-14 years. In the early stages the patient does not require therapy but regular blood counts are performed to monitor the disease for increased activity.

Diagnosis is based on peripheral blood finding of lymphocytosis with cell marker analysis to demonstrate a monoclonal B cell population with light chain restriction. Bone marrow biopsy is not essential for diagnosis but is useful to determine bone marrow reserve and possibly outcome prediction.

The indications for treatment are:

• bone marrow failure with anaemia, neutropenia or thrombocytopenia • bulk disease with lymphadenopathy and/or hepatosplenomegaly • constitutional symptoms such as fever, weight loss, night sweats • autoimmune complications, usually haemolytic anaemia

Predictors of a poor outcome:

(i) clinical stage, RAI or Binet staging system � >3 nodes with bone marrow failure: mean survival 2 years � >3 nodes: mean survival 7-8 years � <3 nodes with normal haemoglobin and platelets: approaches age-matched control survival. (ii) lymphocyte doubling time <12 months (iii) abnormal karyotype on chromosome analyses (iv) marrow infiltration pattern, nodular being better than diffuse


Treatment is not given on the basis of the high lymphocyte count alone. Initial therapy usually involves the alkylating agent chlorambucil with or without prednisone. Fludarabine is one of a new group of agents which is an alternative first line treatment for CLL.

Chronic myeloid leukaemia (CML)

CML is predominantly a disorder of middle life but the diagnosis is being made increasingly in younger patients. The disorder is characterised by a leucocytosis which is left shifted, typically showing the major increases in myelocytes and segmented neutrophils giving a bimodal differential white cell distribution. Blast cells are also present. The majority of patients are Philadelphia chromosome positive. The NAP score is low or absent.

CML is a state of bone marrow instability and after a variable time, median 3-4 years, the disease transforms into an acute leukaemia which is unresponsive to standard chemotherapy. The only potentially curative treatment is bone marrow transplantation. This may use a matched sibling donor or a matched unrelated donor transplant. Interferon is the treatment of choice in patients who cannot undergo bone marrow transplantation. Hydroxyurea is frequently used for cytoreduction.

Chyluria

specimen: random urine, ask for triglyceride.

Chyluria is due to blockage of lymphatics, usually by filaria but sometimes by malignant disease. The urine is milky due to triglyceride-rich chylomicrons in the lymph.


Chryseobacterium see Flavobacterium

A gram-negative bacillus resembling Pseudomonas, formerly known as Flavobacterium. A pathogen in the urinary tract, it may also cause superficial skin infections after contact with soil or fresh water. C. meningosepticum is known as a cause of neonatal meningitis. Isolates are susceptible to vancomycin which is unusual for gram-negative species.

Citrobacter

A gram-negative enteric bacillus which most commonly causes urinary tract infection. Other types of infection include nosocomial pneumonia, septicaemia and wound infections. Treatment is according to susceptibility results.

CK (creatine kinase) total

specimen: serum ref. range: female 30-180 U/L male 60-220 U/L

Elevations of CK

These are common and most arise from skeletal muscle. Clinically the elevations in myocardial infarction are important.

From skeletal muscle


• muscular exercise � the commonest cause. Well-muscled individuals, with or without regular exercise, tend to have levels at or above the upper end of the reference range. Acute bouts of more severe exercise will give elevations of variable extent and duration which may last a week after one episode. There is wide individual variation but levels can rise as high as 4000 U/L in severe, unaccustomed exercise.

• muscle trauma � IM injections (even 1ml), accidents, bruising, physical violence

• acute viral infections � particularly those with myalgia

• alcoholism � even when there is no overt myopathy

• hypothyroidism � and other endocrinopathies

• muscular dystrophies

• polymyositis, dermatomyositis, connective tissue disorders

• tumours � some malignant tumours cause massive increases in CK

• surgery � levels return to normal in 1 week

• parturition � elevated for up to 6 weeks

• acute psychoses

• drugs � fibrates, statins, captopril, colchicine, isotretinoin, lithium, beta blockers

• renal failure

From cardiac muscle

In MI (myocardial infarction), CK typically starts to rise 4-12 hours after chest pain commences and returns to normal in 2-3 days. Myocarditis can cause more prolonged elevations of CK.

see also CK - MB and other isoenzymes Myocardial markers for infarction (MI) and ischaemia


CK - MB and other isoenzymes

specimen: serum, refrigerate if any delay in analysis

ref. range: <4.0 µg/L

relative index <1.0

The three isoenzymes of CK are:

• CK-MM, from skeletal muscle, makes up >94% of total CK

• CK-MB, comes from cardiac muscle but with a small contribution from skeletal muscle

• CK-BB from brain is found in low concentration and is clinically unimportant except occasionally in tumours.

Except when myocardial infarction is a possibility, an elevated CK total can be assumed to be CK-MM from skeletal muscle.

CK-MB in myocardial infarction (MI)

This test has now been superseded by Troponin T or Troponin I which have better specificity and stay high for 7-10 days.

CK-MB rises 4-10 hours after MI and stays high for 36-48 hours.

Interpretation CK-MB Rel. indexMI excluded <4.0 <1.0MI probable >4.0 >2.0MI inconclusive >4.0 & CK total >400 <2.0


The relative index is the CK-MB expressed as a % of total CK.

see also Troponin I (TnI) and Troponin T (TnT) Myocardial markers for infarction (MI) and ischaemia

CLL see Chronic lymphocytic leukaemia (CLL)

Clostridium difficile

A normal inhabitant of the bowel which can proliferate when other organisms are suppressed by antibiotics, particularly clindamycin or ampicillin. C. difficile produces toxins causing bloody diarrhoea and pseudomembranous colitis visible on endoscopy. Less severe forms of antibiotic-associated diarrhoea may also be associated with C.difficile.

Management Stopping the precipitating antibiotic treatment may be enough. The most commonly used treatment is metronidazole, 400mg 8-hourly for 7-10 days. Up to 20% of patients relapse. This is not due to metronidazole resistance but is explained by the ability of C. difficile to form antibiotic resistant spores. The treatment for relapse is again metronidazole.

CML see Chronic myeloid leukaemia (CML)


CMV see Cytomegalovirus (CMV)

CO see Carbon monoxide

CO2 see Bicarbonate

Blood gases & pH

COAD/CORD (chronic obstructive airways/respiratory disease) see Bronchitis, acute or chronic

Coagulation factor assays see von Willebrand's disease (vWD)

Fibrinogen


Coagulation screen

The basic screen consists of:

• platelet count

• bleeding time for platelet function

• PR (prothrombin ratio) for extrinsic pathway

• APTT (activated partial thromboplastin time) for intrinsic pathway

• TCT or fibrinogen assay for final common pathway

Two other tests done at the same time are:

• blood count, to detect other haematological abnormalities

• liver function tests to exclude liver disease as a cause of coagulation factor deficiency

These tests may miss mild abnormalities but they will detect major disorders. More detailed investigations may more fully characterise an abnormality and are indicated where there is a strong bleeding history.

What are the common abnormalities?

This laboratory does about 6000 screens each year. Diagnoses and their frequencies are:


diagnosis % of total

bleeding history but normal laboratory tests 66isolated long APTT 10congenital platelet function defect 8acquired platelet function defect 5von Willebrand's disease 4lupus anticoagulant 2vitamin K deficiency 2liver disease 2other factor deficiency 1

The importance of the bleeding history

A careful history is the most valuable part of an assessment. If the history of bleeding is convincing, a minor disorder may exist even if the laboratory tests are normal.

Ask specifically about

· epistaxis especially if bilateral, recurrent, or requiring repeated cautery. Unilateral epistaxis is often due to a local lesion.

· bruising specify size and whether spontaneous or traumatic.

Trunk and upper arm bruising are potentially more important than lower limb bruising. Deep bruising with central induration is significant.

· lacerations particularly recurrent and prolonged bleeding · surgery wisdom tooth extraction, tonsillectomy, other major

surgery, blood transfusion requirement, prolonged postoperative hospital stay

· menorrhagia a bleeding disorder may potentiate anovulatory

menhorragia · gum bleeding when brushing teeth


· family history suggests inherited disorder · drugs specifically ask about medication for headaches,

arthralgias, particularly aspirin, NSAIDs

Coefficient of variation (CV) see Variation

Coeliac disease (gluten sensitive enteropathy)

Coeliac disease, affecting at least 1:3000 (1:300 in some populations) is by far the commonest cause of intestinal malabsorption.

In severe cases it presents in infancy or childhood with failure to thrive and fatty diarrhoea.

Milder cases are more common and can easily be overlooked, particularly as many do not have intestinal symptoms. Features of these milder cases can be one or more of:

• anaemia • iron deficiency • folate deficiency • fatigue • diarrhoea, abdominal discomfort

The disease is due to an intolerance to gliadin (gluten) found in wheat, barley and rye. Diagnostic antibodies are found in serum, and the mucosa of the small intestine shows flattened villi on biopsy. Withdrawal of gluten from the diet usually results in


symptomatic improvement, normalisation of villi and disappearance of antibodies over the course of a year or so.

Dermatitis herpetiformis, which presents as a chronic pruritis papulovesicular skin rash, is a cutaneous manifestation of gluten sensitivity with the same diagnostic antibodies and improvement on gluten withdrawal.

Diagnosis 1. Antibodies

These simple, relatively specific tests developed over the past few years have improved the detection rate in patients whose symptoms do not justify intestinal biopsy.

� anti-gliadin antibodies (AGA) are sensitive but show significant false

positives

� endomysial antibodies (EMA) are highly specific but less sensitive

� reticulin antibodies are less often used but have a high degree of pecifity when positive

All three are measured as the IgA antibody, which correlates with disease better than the IgG, except in patients with selective IgA deficiency (10x more common in coeliac patients) where the IgG antibody must be used. To identify IgA deficiency, immunoglobulins must be measured.

If both AGA and EMA antibodies are positive, predictive value for coeliac diseaseis >99%. Where only one test is positive, the likelihood of coeliac disease is less.

As noted above, antibodies can disappear when a gluten-free diet is successfully implemented. Reappearance of antibodies can indicate changed dietary compliance.

2. Other tests � malabsorption


blood count s. iron, IBC and ferritin s. folate fat: check 3-day faecal fat � small intestinal biopsy for definitive diagnosis 3. Trial of gluten-free diet

Cold agglutinins

specimen: serum from blood collected at laboratory and stored at 37ºC prior to analysis.

Cold agglutinins are autoantibodies that cause red cell agglutination in the temperature range 0-37ºC. Clinically harmless cold agglutinins in low titre may be an incidental laboratory finding.

In cold haemagglutinin disease , higher titres of an IgM antibody lead to complement-mediated haemolysis and may be associated with Raynaud's phenomenon.

An even rarer condition is paroxysmal cold haemoglobinuria in which the Donath-Landsteiner antibody causes intravascular haemolysis, sometimes severe, following exposure to cold.

These cold autoantibody diseases can be either primary, when they are usually found in older patients, or secondary. The secondary associations are infections (infectious mononucleosis, mycoplasma, CMV); lymphomas or CLL; or connective tissue diseases. The prognosis of secondary cold haemagglutinin disease is that of the underlying disorder.


Serum protein electrophoresis may show a monoclonal paraprotein, particularly when associated with malignant disease, or the agglutinin may be polyclonal.

see also Cryoglobulin & cryofibrinogen

Complement, C1 inhibitor (C1 INH) specimen: serum

ref. range: antigenic 0.15-0.35 g/L

functional 5-10 U/ml

C1 inhibitor is a complement inhibitor that is deficient in quantity and/or activity in 85% of patients with hereditary angi-oedema. Complement C4 is almost invariably reduced, even between attacks.

Complement fractions C3 and C4 specimen: serum � must be separated within 1 hour and frozen

ref. range: C3 0.8 � 1.8 g/L C4 0.2 � 0.4 g/L

The complement system is a cascading series of plasma proteins whose end-products cause bacterial lysis and remove the immune complexes found in post-streptococcal glomerulonephritis, SLE and other autoimmune disease. There is reduction of C3 in PSGN and of both C3 and C4 in SLE. They are increased in most other inflammatory states.


Complete blood count (CBC) see Blood count

Congenital adrenal hyperplasia (CAH)

A group of inherited adrenal disorders due to enzyme defects, the commonest being 21-hydroxylase deficiency. Neonatal blood screens check for severe forms of 21-hydroxylase deficiency by measuring 17 OH-progesterone.

Severe CAH can present as hypokalaemia and dehydration in neonates; as virilisation in a female child; or as precocious puberty in males.

A milder and more common form of CAH can present as hirsutism in adult women. It can be detected by measuring serum 17 OH-progesterone on a morning specimen collected during the follicular phase of the menstrual cycle.

see also � 17-hydroxy progesterone (17-OHP)

Conjugated bilirubin see Bilirubin, conjugated (direct) and unconjugated (indirect) fractions

Connective tissue diseases


A group of systemic autoimmune diseases characterised by the presence of fairly non-specific autoantibodies and associated with chronic inflammation of musculoskeletal structures. The main diseases are:

• rheumatoid arthritis (1-2% of the population) • SLE, systemic lupus erythematosus, (0.1% of the population) • Sjogren's syndrome • diffuse scleroderma (0.002% of the population) • local scleroderma (CREST) • mixed connective tissue disease (MCTD) • dermato/poly/myositis

Tests associated with these conditions are described under the disease headings.

Diagnosis can be difficult or impossible in the early stages of these conditions which can evolve over months or years before enough features develop to establish the diagnosis.

Conn's syndrome see Aldosterone and renin, plasma

Coombs test specimen: serum

The Coombs test detects antibodies directed against red cells.

The direct Coombs test detects antibodies or complement which are coated on red cells as in autoimmune haemolytic anaemia, haemolytic disease of the newborn,


incompatible transfusions, or drug-induced haemolysis, particularly that due to methyldopa or penicillin in large doses.

The indirect Coombs test detects red cell antibodies in serum, as in maternal antibody screens in pregnancy or some autoimmune haemolytic anaemias. It is also used in cross-matching.

Copper specimen: serum or urine, 24-hr in special plastic bottle from laboratory containing 25ml

purified HCl ref. range: serum 13-22 µmol/L urine <1.2 µmol/day

Wilson's disease is an autosomal recessive disease due to accumulation of copper in the body in toxic amounts. It presents usually at age 5-20 with unexplained liver disease, neurological or psychiatric symptoms, or Kayser-Fleischer corneal rings. There is an increased excretion of urine copper, but reduced serum copper. This is because ceruloplasmin (qv), the protein which transports copper in serum, is reduced in Wilson's disease even though the total body load of copper, and its urinary excretion, are markedly elevated.

S. copper is reduced in protein-losing states and raised by oestrogens, pregnancy, or inflammatory states.

Coproporphyrin see Porphyrias


Cord blood testing

When haemolytic disease of the newborn (qv) is suspected, Hb, blood group, direct Coombs and bilirubin must be checked. Otherwise cord blood samples are not routinely tested though some collect the samples and store them for up to a week at 4°C in case they should be needed.

When the direct Coombs is positive, Rh typing must be confirmed and the coating antibody identified. The initial Rh typing will sometimes be found to be incorrect when the direct Coombs is positive, due to interference by the antibody.

Cord blood reference ranges for a wide variety of tests differ markedly from those found in the next few hours, days and weeks of life. See individual test entries for particular ranges. The three commonest tests on cord blood and their reference ranges are:

Hb 136–196 g/Lbilirubin full-term up to 50 µmol/L

premature up to 25 µmol/Ldirect Coombs negative

Cortisol, serum specimen: serum collected at 07.00 � 10.00 hrs

ref. range: 200�700 nmol/L

There is marked diurnal variation, the peak at 09.00 hrs being 50-100% higher than the trough at 23.00 hrs.

An isolated 09.00 serum cortisol is a crude diagnostic tool. A rough guide to interpretation:


<150 strongly suggests adrenal insufficiency150-200 further assessment indicated for possible

adrenal insufficiency200-550 adrenal insufficiency not excluded

Cushing's syndrome unlikely550-700 adrenal insufficiency unlikely

Cushing's syndrome possible>700 Cushing's syndrome possible but there

are commoner causes of raised cortisol

Decreased levels

• primary adrenal insufficiency (Addison's disease)

• secondary deficiency follows adrenal suppression by steroid therapy

• drugs � ketoconazole, phenytoin, metyrapone, steroids

• decreased cortisol-binding proteins

• hypopituitarism

• exogenous steroids (variable) Elevated levels

• Cushing's syndrome � pituitary adenoma or hyperplasia � adrenocortical tumour � ectopic ACTH from malignant tumour • stress, illness, depression, alcoholism • oral contraceptives, oestrogens, pregnancy • exogenous steroids (variable) • increased cortisol-binding proteins

Cortisols are of lmited value when monitoring replacement therapy.

see also Adrenocortical insufficiency


Cushing's syndrome

Cortisol, urine free specimen: 24�hr urine, no preservative

ref. range: 110�330 nmol/day

Because only the unbound fraction of serum cortisol reaches the urine, this is a good screen test for Cushing's syndrome and a clearly normal result makes the diagnosis unlikely. In perhaps 10% of cases cortisol hypersecretion is intermittent.

Elevations up to 3x normal may be found in stress, depression or alcoholism.

Urine cortisol is not used in suspected adrenal insufficiency.


Corynebacterium diphtheriae

The latest Auckland case was in July 1998. A special medium is required to recover C. diphtheriae so the possibility of diphtheria must be specifically mentioned on the request form.

Tonsillar diptheria is still occasionally seen in non-immunised persons. Skin infections with C. diphtheriae occur in the tropics and can be a source of infection.

Corynebacterium haemolyticum see Arcanobacterium haemolyticum

Corynebacterium minutissimum see Erythrasma

Coxsackie viruses

These are widely distributed enteroviruses associated with many different types of illness including minor febrile illnesses, the common cold, herpangina, pleurodynia, aseptic meningitis, myocarditis, post-viral fatigue syndrome, conjunctivitis, Type I diabetes and others. Infections are more common in summer and autumn. Virus can be recovered from throat swabs or rectal swabs and also conjunctival or vesicular swabs if lesions are present.


C-peptide, plasma or urine

C-peptides are fragments derived from endogenous, but not exogenous, insulin. Formerly used to check residual islet cell function in Type 1 diabetes or in the investigation of unexplained hypoglycaemia but now rarely used.

CPK (creatine phospho-kinase) see CK (creatine kinase) total

C-reactive protein (CRP) specimen: serum

ref. range:

mg/L

<5 normal10 - 40 mild inflammation, some viral infections40 - 200 acute inflammation, bacterial infections>200 severe bacterial infection or extensive trauma

CRP is the most useful of the acute phase reactants, rising sharply 4-8 hours after tissue damage by infection, infarction, inflammation or trauma. It returns to normal 2�3 days after disease activity has ceased. It can be regarded as a fast-changing ESR which, by contrast, rises and falls more slowly. It can be used as an indication of occult bacterial infection, suspected rheumatic fever, inflammatory bowel disease or other conditions where there is uncertainty whether symptoms are functional or due to organic disease. Chronic inflammatory diseases such as SLE can be monitored using serial CRPs and for this purpose it is a more useful test than the ESR. It has also been used in the diagnosis of myocardial infarction.


Creatine

specimen: 24-hr urine, no preservative

A disused investigation for muscle disease, CK being a better test.

Creatine kinase see CK (creatine kinase) total

Creatine phosphokinase (CPK) see CK (creatine kinase) total

Creatinine, serum specimen: serum

ref. ranges:

age mmol/L

newborn 0.020 - 0.090child 0.020 - 0.070adolescent 0.040 - 0.090adult female 0.050 - 0.105adult male 0.060 - 0.120

Some laboratories use µmol/L which would make the adult female range, for example, 50 - 105.


S. creatinine is widely used as a test of renal function both as a general screen, along with urine protein, for renal disease, and as a test for serial monitoring of renal function where there is potential or actual renal disease.

It reflects glomerular filtration rate (GFR).

s. creatinine α GFR

1

It also reflects endogenous creatinine formation from skeletal muscle and to a much lesser extent, exogenous creatinine excretion from cooked meat.

GFR steadily reduces with increasing age but this is offset, though not completely, by diminishing muscle bulk and creatinine excretion.

The use of a population-based reference range is even less satisfactory for creatinine than for other analytes because the individual creatinine range for a person remaining in good health is narrower than the traditional population range. When monitoring a potentially nephrotoxic process, reference should always be made to the individual's own range, as shown by creatinine results when disease-free, rather than to the population range.

Uses of serum creatinine

• as a crude basic screen of renal function • for establishing an individual's baseline creatinine range • monitoring potentially nephrotoxic drugs, particularly in the elderly�

NSAIDs � ACE inhibitors � aminoglycosides � diuretics � lithium


� and others • monitoring potential nephropathy e.g. in diabetics • monitoring established renal disease • monitoring renal transplant rejection • monitoring renal dialysis

Method interference

Cephalosporins and ketosis give a falsely high creatinine.

Hyperbilirubinaemia (>200 µmol/L) gives a falsely low value.

Cimetidine, probenecid and trimethoprim can raise creatinine temporarily by reducing tubular secretion.

Pre-renal disease When shock, cardiac failure, fluid & electrolyte depletion, reduce renal blood flow, s. creatinine will rise.

Post-renal obstruction

Usually prostatic, will eventually raise s. creatinine.

Creatinine, urine specimen: 24-hr urine, no preservative ref.ranges:

adult female 4.0 - 17.0 mmol/dayadult male 7.0 - 24.0 mmol/day


24-hr urine creatinines are used when estimating creatinine clearance.

Wide variations in creatinine output for an individual are due to biological variation of ± 20%, sometimes compounded by incomplete (or over-complete) urine collects.

A creatinine concentration in a spot urine gives a way of compensating for urine concentration when expressed as the ratio, analyte/creatinine e.g. ACR (albumin/creatinine ratio) in diabetics.

Creatinine clearance specimens: 24�hr urine, no preservative � must be accurately timed to 24 hrs, no more, no less. plus serum obtained within collection period

ref. range: female >1.2 ml/sec/1.73m²

male >1.5 ml/sec/1.73m² after age 40, clearance drops by about 0.1ml/sec/decade

Creatinine clearance is used as a measure of GFR (glomerular filtration rate) where early renal impairment is suspected. Because collecting a 24-hr urine is inconvenient and often inaccurate, the serum creatinine alone is often used as a GFR proxy.

The day-to-day variance is about 20%.

The formula for calculating clearance is :

areasurface73.1

x.conc.creat.s

volumex.conc.creat.urclearancecreatinine =

For an adult of average build, correction is unnecessary but it is essential in children.

A useful approximation in children is:

1500xcreatinine.scmin.ht

)m73.1/sec/ml(GFR 2 =


The Cockroft & Gault formula provides an estimate of creatinine clearance based on age, weight, sex and s. creatinine without the need for urine collection.

sec/ml000,50x)L/mmol(creatinine.s

)kg(weightx)age140(clearancecreatininemale

-=

for females, same formula x 0.85

CREST syndrome

• Calcinosis

• Raynaud's phenomenon

• Esophageal hypomotility

• Sclerodactyly

• Telangiectases

Also called limited scleroderma. The ANA is usually positive showing the centromere pattern.

Crohn's disease

Laboratory abnormalities can include:

• iron deficiency

• vitamin B12 deficiency

• anaemia due to combinations of chronic disease and iron and B12 deficiency

• raised ESR and CRP

• reduced albumin

• hypokalaemia


Crossmatch

specimen: blood (plain tube)

For routine pre-operative cross-matches for cold surgery, the specimen must be collected at least 24 hours in advance. There are some essential prerequisites:

• The request must be made on cross-match request forms in duplicate (one can be a carbon copy).

• Full ID on request form � full patient name, dob, sex, NHI number if known.

• Full patient ID on specimen tube and date and time of collection.

• Doctor's name and signature and date of request on both copies.

• Time and date of specimen collection. If the patient has been transfused in the past 14 days, specimen collection and cross-match must be done within 24 hours of operation.

• Patient's hospital

• Indicate whether 'group and hold' only

• If packed cells or whole blood required, indicate number of units

• Time and date required

• Give previous transfusion history, history of red cell antibodies, obstetric history.

Laboratory procedure The donor red cells are tested for compatibility with the patient's serum.


CRP see C-reactive protein (CRP)

Cryoglobulin & cryofibrinogen

specimens: serum (plain tube) for cryoglobulins

plasma (heparin) for cryofibrinogen and blood (EDTA)

Specimens must be kept collected at the laboratory to maintain them at 37°C prior to analysis.

see Cold agglutinins

Cryptosporidium

Cryptosporidium is now recognised as a cause of acute gastroenteritis, particularly in children. It is a notifiable disease. Recent figures for New Zealand show a population attack rate of 20/105 with the highest rates for children: 35/105 for those under 1 and 70/105 for 1-4 year olds. It is found in a variety of hosts and transmission from farm livestock or pets to humans can occur. Person to person transmission also occurs and has been responsible for outbreaks in child care facilities.

Diagnosis is by use of a special stain for oocysts in faeces and will be done on specific request. The typically watery diarrhoea usually settles without treatment within 10 days (range 1-20 days). In immunocompromised patients (especially those


with HIV), it may cause a severe prolonged diarrhoeal illness. In this situation specialist advice should be sought on treatment.

CSF (cerebrospinal fluid) specimen: collect into sterile tubes

ref.ranges:

cells <5 mononuclearsno neutrophilsno red cells

glucose >5 mmol/Lprotein <0.45 g/L

The microbiology department should be notified if meningitis is a possibility so that the specimen can be handled urgently.

CSF cytology

CSF specimens for cytology need to reach the laboratory within 30 minutes of collection. Please contact the laboratory prior to lumbar puncture if CSF cytology is required.

Cushing's syndrome The main causes are:

• excess ACTH (adrenocorticotrophic hormone) produced by the pituitary


• excess ACTH produced by non-endocrine tumour particularly Ca lung

• adrenal tumours

Basic screen test: 24�hr urine free cortisol (qv)

Follow-up test: dexamethasone suppression test (qv)

Isolated serum cortisol is not recommended as a screen test though a level below 500 nmol/L in a specimen collected before 10.00 hrs makes Cushing's unlikely.

Clinical features of Cushing's include obesity, diabetes, hypertension, plethora, muscle weakness, striae and osteoporosis.

CV (coefficient of variation) see Variation

Cyclical neutropenia see Neutrophils (polymorphs)

Cyclospora cayetanensis C. cayetanensis is a recently described protozoan which causes diarrhoea in travellers to endemic areas. It is common in Nepal. The incubation period is 3-11 days, median 8 days. It causes a protracted and relapsing diarrhoea. Range of illness is 9-40 days. Diarrhoea may last for months in the immunocompromised. Diagnosis is by


detecting acid fast oocysts in stool. The treatment of choice is cotrimoxazole, two tablets 12 hourly for 7 days.

Cystic fibrosis

Affects 1:3000 infants. Cystic fibrosis is carried on a recessive gene which can be identified in 70% of carriers by DNA testing. The underlying defects of exocrine gland function show up in respiratory tract, pancreas and sweat glands. Typically, presentation is in infancy or childhood with recurrent pulmonary infections and sometimes with malabsorption.

All newborns in New Zealand are screened for cystic fibrosis by measuring blood trypsinogen on the NTC (National Testing Centre); (qv) blood spots collected in the first week of life. Pick up rate is 98%. The test can be used up to the age of 6 weeks. Because false positives are relatively common, positive tests must be checked at 6 weeks.

There are two definitive tests:

• Sweat electrolytes (qv) � high Na+ and Cl- levels

• Identification by DNA testing of a CF gene which is present in 70% of cases. Tests are being developed for the remaining 30% and prenatal DNA testing is being used to identify affected foetuses.

Cys 282 mutation see Haemochromatosis


Cystinuria

specimen: random urine for screen test

24-hour urine for quantitation ref. range: <420 µmol cystine/day

Cystinuria with an incidence of 1:10,000 is the one of the commonest of the inborn errors of metabolism. Failure of the renal tubules to reabsorb cystine from urine results in excretion of a high concentration of poorly soluble cystine which can precipitate to form cystine stones � 1-2% of all renal calculi.

Cytogenetics Three major areas of testing are carried out:

1. Prenatal diagnosis from: � amniotic fluid � chorionic villi 2. Clinical diagnostic work for cases of: � infertility or multiple miscarriages � stillbirth (where clinical indicators are present) � babies with multiple malformations, with or without neurological

dysfunction � children with an unusual appearance who are developmentally delayed

or mentally retarded, especially if there are co-existing congenital defaults

� in some children with speech delay, behavioural problems, isolated mental retardation

� genital abnormality, hypogonadism 3. Cancer cytogenetics: � leukaemia � lymphomas


� solid tumours

Cytology see Cervical cytology Aspirated fluids, synovial, pleural,

ascitic etc from cysts or pleural or ascitic fluid

Bronchial brushings or washings CSF (cerebrospinal fluid) Fine needle aspirate (FNA) Frozen section/rapid smears Gastric and oesophageal

brushings/washings for cytology Sputum cytology Ulcer scrapings for cytology particularly

from the oral cavity Urine cytology

Cytomegalovirus (CMV)

specimen: serum

Interpretation

IgM antibodies, reported as +ve or �ve, are detectable for a period of about 6 months from the time of commencement of a CMV infection. False positives occur during some other viral infections, notably those due to EBV.


IgG antibodies, reported in units/L, become detectable soon after the commencement of infection and remain positive for life, usually at a level >20 units/L. A rising titre in paired sera is the best evidence of current infection. Most adults are IgG CMV positive indicating previous infection.

The virus itself persists in latent form throughout life after recovery from the initial infection and can be reactivated in an immunocompromised patient.

Clinical infection can present in several ways:

• subclinical infection is common, particularly in childhood.

• a mononucleosis-like syndrome is found in adolescents and young adults, spread by sexual and other intimate contact. CMV differs from EBV mononucleosis in its absence of heterophile antibodies. Exudative pharyngitis and cervical lymphadenopathy are rare. The illness can be severe with fevers and profound fatigue lasting several weeks and the virus can cause hepatitis. As in EBV infections, variant lymphocytes are a feature.

• Congenital infections range from inapparent to severe with congenital abnormalities or intrauterine death. Diagnosis is by identifying the virus in urine collected during the first week of life.

• Immunocompromised patients can develop severe generalised disease.

D


D-Dimers specimen: plasma (citrate)

ref. range: <200 µg/L

D-dimer is a fibrin break-down product and elevated levels can be found in any situation where there is thrombosis.

Clinically the test is used when DVT (deep vein thrombosis) with or without PE (pulmonary embolism) is suspected. A normal D-dimer level makes DVT/PE unlikely.

Elevated levels have a poor predictive value for DVT/PE as they are found in many clinical situations including chronic inflammatory disorders, malignancy, post-operative states and acute rheumatic conditions.

Dehydroepiandrosterone sulphate see DHEAS (dehydroepiandrosterone sulphate)

Demodex folliculorum

This is an extremely small mite (0.3-0.4mm), which inhabits the hair follicles and sebaceous glands of humans. They feed on sebaceous secretions, especially sebum. They are particularly common on the nose, eyelids and cheeks.

The life cycle from egg to larvae to nymphs to adults takes around two weeks and occurs within the hair follicle or sebaceous gland. A high proportion of adults,


especially women, unknowingly have these mites. They are seldom found on children or adolescents.

They do not normally appear to produce disease. There are conflicting reports on their association with rosacea.

It has been associated with ocular itching and blepharitis in the elderly but its importance as a cause is disputed.

Treatment: There is little to suggest that treatment is indicated for this endemic human infestation.

Dengue antibodies specimen: serum

Dengue, a painful febrile illness ("break-bone fever") caused by a mosquito-borne arbovirus, is found all over the Pacific including Fiji. Typically it occurs in outbreaks but can be sporadic.

Diagnosis is by measuring IgM and IgG antibodies preferably in paired sera. Although both antibodies may date back to an earlier infection, the ratio of IgM to IgG, or rising titres in paired sera, will help decide whether infection is recent.


Dermatophytes

The three dermatophytes � Trichophyton, Microsporum and Epidermophyton � invade keratin in skin, nails and hair. They have their sites of predilection but any of them can be found at any site.

Microsporum species are usually transmitted by animals and are the common cause of scalp ringworm in children.

Epidermophyton is transmitted from person to person and most commonly affects the groin.

Trichophyton has three modes of transmission from soil, animals or humans and is found in hair, nails and skin.

The clinical picture and treatment are, however, determined more by site than by species and in the discussion that follows, the dermatophytes will be treated as if they were a single fungus.

The task of the laboratory is to answer the question "Is this skin lesion due to a fungus?". False positive answers and false negatives are equally undesirable. A false positive may subject the patient to a long and expensive course of treatment. A false negative answer may lead to unsuitable treatment such as a steroid which will exacerbate the underlying fungal infection. There are three important steps in laboratory diagnosis:

Specimen collection An adequate amount of keratin must be collected from the area of the lesion where fungal growth is most likely to be active. The importance of collecting an optimum specimen cannot be over-emphasised.


Microscopic examination Demonstration of hyphae in a KOH wet film can immediately establish the presence of a fungus.

Fungal culture Growth of a dermatophyte, taking up to 3 weeks, will pick up those infections where hyphae have not been found on initial microscopy. Although the laboratory keeps cultures for 3 weeks, most positives are reported after 1-2 weeks.

Superficial mycoses by site

The typical fungal skin infection is an irregular expanding ring with a raised serpiginous border thought to resemble a worm, hence the old term ringworm or tinea (latin for worm). Scrapings of keratin must be collected from the periphery where the infection is active. Sometimes there is a secondary bacterial infection obscuring the fungus, a situation seen particularly in athlete's foot.

Manifestations of fungal infections vary considerably by site.

Trunk and limbs � tinea corporis

These usually present the classical appearance described above. They are usually cured within 2 weeks by topical antifungals such as terbinafine, clotrimazole, miconazole or econazole. It is recommended to continue treatment for several days after full resolution of the lesions. Where chronic or widespread infection is present, oral terbinafine, itraconazole or fluconazole may be considered.

Scalp � tinea capitis

Infected hair may break leaving a bald area. Fluorescence under a Woods lamp sometimes helps establish the diagnosis and indicates which hairs should be taken for microscopy and culture. Treatment with an oral agent is recommended, e.g. terbinafine or itraconazole.


Groin � tinea cruris

Lesions may be on the inside of the thighs, inguinal area, pubic hair or scrotum. Candida infections are common here as in other moist warm folds and a swab should also be collected and placed in transport medium. Topical imidazoles are effective against both Candida and dermatophytes. Erythrasma (qv) may be found in the groin and is sometimes mistaken for tinea.

Athlete's foot � tinea pedis

Although the initial infection can be dry and scaling, added bacterial infection and accumulation of soggy debris may occur. Treatment requires attention to hygiene and local applications. Bear in mind Candida can be implicated as well as bacterial superinfection.

Nail � tinea unguium, onychomycosis

Dermatophytes may affect the nails alone or they may spread from a nearby skin infection. The nail often becomes thickened, discoloured and friable. Scrapings, clippings and debris should be collected. Collection of a good specimen is of particular importance in this site because long-term oral treatment may be needed. Treatment options include oral terbinafine or itraconazole. Yeast species such as Candida (qv) and other non-dermatophyte fungi may also cause nail infections.

Palms and Soles Dermatophytes can be the cause of dry scaly lesions of palms and soles. Specimens need to be collected with care to avoid false negatives. Treatment is topical.

Tinea versicolor


Malassezia furfur (qv) causes this fungal infection which presents as skin discoloration without inflammation or itching. Treatment is with a topical imidazole, ciclopiroxolamine or terbinafine. Oral terbinafine is not effective.

Dexamethasone suppression test

specimen: serum protocol: day 1, give 1 mg dexamethasone orally at 23.00 hrs day 2, collect specimen at 08.00-09.00 hrs ref. range: <130 nmol/L at 09.00 hrs post-suppression

Normal suppression, especially to <50 nmol/L makes Cushing's syndrome unlikely.

Failure to suppress is less helpful and may occur with a range of conditions including:

• Cushing's syndrome • endogenous depression • chronic alcoholism • drugs � phenytoin, barbiturates, oestrogens • significant stress or illness

DHEA see DHEAS (dehydroepiandrosterone sulphate)

DHEAS (dehydroepiandrosterone sulphate) specimen: serum


ref. range: adult female 0.4-5.8 µmol/L adult male 2.8-9.6 µmol/L DHEA and its sulphate DHEAS are the most abundant androgenic steroids secreted by the adrenal cortex. DHEAS is more commonly measured than DHEA and for practical purposes the two estimations provide the same information. Its uses are:

• in the investigation of virilism - levels are usually >3x upper limit of normal • in the investigation of hirsutism when there is a more than 2-fold increase in

free testosterone • to differentiate Cushing's disease (minor elevations of DHEAS) from adrenal

neoplasms where there are large increases • for monitoring steroid suppression therapy in congenital adrenal hyperplasia.

DHEAS is not used as a first-line investigation in mild to moderate hirsutism. Mild elevations up to 30% are common but do not affect management.

In people taking DHEA supplements to restore youth and beauty, the DHEAS levels may be increased 2-3x.


Diabetes autoantibodies specimen: serum

ref. range: antibody significant level— GAD (glutamic acid decarboxylase) > 10 units— IA2 (insulin antigen 2) > 8— ICA (islet cell antibody) > 10— IA (insulin antibody) > 3

These autoantibodies are markers for Type 1 diabetes and typically can be detected months or years before the development of clinical disease.

Indications

As yet a generally accepted preventive treatment for pre-clinical diabetes has not been found but when it is there will be screening programmes and preventive treatment for those who have significant levels of one or more antibodies.

At present autoantibodies are measured in two situations:

• to help predict whether a child of a Type 1 parent will develop diabetes. • to determine whether a newly-diagnosed adult (particularly young adult) has

Type 1 or Type 2 diabetes, though in practice antibodies are not often used because the typing is clinically apparent.

The preferred initial screen is for GAD and IA2 antibodies which are the easier tests technically and the ones most likely to be elevated.

see Diabetes mellitus (DM), classification


Interpretation

The autoantibody pattern is variable from one patient to the next and varies with time for an individual patient. GAD antibodies have a higher positivity rate (~80%) than the others and stay elevated for longer

ICA and IA appear earlier in the pre-clinical course of the disease and disappear earlier.

One antibody just above the level of significance may disappear without diabetes developing.

A high level � they can be up to 50 times the significant level � is more likely to progress to diabetes.

Two or more antibodies are more predictive than one.

Risks for developing Type 1 DM (diabetes mellitus) are:

identical twin has Type 1 DM 40% both parents Type 1 DM 20% father Type 1 DM 8% sibling Type 1 DM 5% mother Type 1 DM 3% general population 0.3%


Diabetes insipidus

The essential feature is inadequate ADH (antidiuretic hormone) from the hypothalamus/posterior pituitary causing excessive loss of dilute urine from the kidney; or a kidney which is unresponsive to ADH. The usual problem is to separate compulsive water drinking or simple urinary frequency from true diabetes insipidus in a patient complaining of polydipsia and polyuria.

• Other causes of polyuria need to be eliminated. � diabetes mellitus � hypercalcaemia � renal disease � medication: lithium, diuretics

• A 24-hr urine should be collected to check whether urine volume is genuinely

excessive e.g. >4L. In severe disease, volume can be as high as 18L. • The final screen test is urine osmolality after 8-12 hours of water deprivation

overnight. A urine specimen is collected on waking and ½-1 hour later before drinking anything, the osmolality in these two specimens indicating ability to concentrate urine.

The person with diabetes insipidus will be excreting a large volume of dilute urine throughout the night compared with the normal person's diminishing volume of increasingly concentrated urine. An osmolality <200 mmol/kg is consistent with diabetes insipidus whereas a value above 400, or better still above 600, makes the diagnosis unlikely.

Water deprivation should not be attempted in the person with a very high urine volume because of the danger of serious dehydration.


Diabetes mellitus (DM)

Classification � Type 1 (formerly IDDM) beta cell destruction associated with

autoantibodies leading to absolute insulin deficiency

� Type 2 (formerly NIDDM) there is insulin resistance with relative insulin deficiency and in some cases absolute insulin deficiency requiring insulin treatment.

� gestational diabetes (GDM) � pancreatic diabetes � pancreatitis, haemochromatosis � endocrinopathies � Cushing's, Conn's, hypothyroidism, phaeochromocytoma,

acromegaly � drug induced � steroids, thiazidess Diagnosis of diabetes

Consider under two headings:

1. Symptomatic (thirst, polyuria, weight loss, tiredness)

The symptomatic patient almost invariably has a glucose level above 15 mmol/L. An interim diagnosis can be made immediately using a urine dipstick, followed by a definitive laboratory blood glucose. Where there is less urgency, a random glucose result above 11.0 mmol/L at the laboratory will confirm the diagnosis.


2. Asymptomatic i.e. screening for diabetes � A fasting glucose is a good screen test and can be combined with fasting

lipids to check risk factors. � Random bloods � A level between 7.0 and 11.0 is an indication for a GTT

(glucose tolerance test) or a fasting test. Below 7.0 can be accepted as probably non-diabetic. Above 11.0 should be followed by a second random glucose, two values above 11.0 being diagnostic of diabetes.

� HbA1c (qv) is a useful test where a random glucose is equivocal and GTT is

impractical e.g. the very busy, the needle-shy or the elderly person in a rest home.

� The 1-hour or 2-hour post-polycose plasma glucose is useful in population

studies but inconvenient for the individual non-pregnant adult � having gone to the trouble they may as well do the full 2-hr diagnostic GTT.

� In pregnancy the 50g polycose (qv) screen test is used. � Urine testing is unacceptable as a screening procedure.

Diagnostic criteria

• classic symptoms and plasma glucose ≥ 11.1 mmol/L

• fasting glucose ≥ 7.0 on two occasions (the 1985 WHO level was 7.8)

• 2-hr glucose level ≥ 11.1 in a GTT.

• two random glucose levels ≥ 11.1.

see Glucose tolerance test (GTT) for more detail


Who should be screened for diabetes?

The NZSSD recommends screening as follows:-

• 5-yearly testing of Europeans over age 40 and non-Europeans over age 30 • frequency increases to 3-yearly if the patient is obese, has a family history of

diabetes or has hypertension. • tests should be done yearly for � post IGT (impaired glucose tolerance)

� post GDM (gestational diabetes)

Detection of pre-clinical Type 1 diabetes see Diabetes autoantibodies

Monitoring diabetes

Patient autonomy is central to successful management and this involves self-monitoring using finger-prick specimens for most Type 1 diabetics and for selected Type 2s.

Type 2s require fewer tests for monitoring, their glucose levels being generally more stable and their treatment regimens more fixed. A four times daily insulin regimen, by contrast, in an unstable diabetic, requires frequent monitoring.

Tests used for monitoring glycaemic controls are:

Plasma glucose Patients who are self-monitoring establish their daily glucose profile by testing before breakfast (fasting), before lunch, before dinner and before bed. When using the laboratory, bearing in mind its more limited availability, the most useful times are before lunch, often the lowest level of the day, and late afternoon.


Patients who are unreliable testers will require more laboratory glucose tests than those who are conscientious self-testers.

HbA1c (qv), which gives a measure of the mean blood glucose level over the past 2 months, is the essential base-line measure of glycaemic control and should be done at least annually in all diabetics.

Fructosamine (qv) may have a role when looking for more recent changes in glycaemic control or when red cell turnover is increased as in chronic bleeding or haemolysis but in general it is a considerably less satisfactory test than HbA1c.

Urine glucose testing has been abandoned as a tool for monitoring.

Urine microalbumin (qv) is used at annual review for detecting early nephropathy.

Diarrhoea, infectious

The common pathogens diagnosed at this laboratory are:

Campylobacter 55% Salmonella 17% Giardia 14% Yersinia 10% Shigella 4%

Rotavirus is the most common pathogen in children under 5 years of age. For more detail on the above organisms, see separate alphabetic entries.

Travellers' diarrhoea


Acute severe diarrhoea � ciprofloxacin 500mg 12-hrly is the treatment of choice supported by careful attention to fluid and electrolyte intake.

Chronic diarrhoea � can be due to giardiasis. Treat with metronidazole 2g daily for 3 days, or tinidazole 2g as a single dose.

Prophylactic antibiotics � these are not recommended as a routine but some travellers suffering repeated bouts of diarrhoea may be helped by doxycycline 100mg daily or cotrimoxazole 480 mg daily.

Diastase The old name for urinary amylase (qv).

Diazepam see Drug screen � overdose

Dibucaine number see Cholinesterase

The dibucaine number detects the qualitative difference in cholinesterase enzymes in scoline-sensitive persons.


DIC (Disseminated intravascular coagulation)

This is an uncommon condition in which there is a generalised consumption of plasma clotting factors and platelets resulting in fibrin deposition within the microcirculation. Secondary haemorrhagic events are due to the consumption of normal clotting factors and secondary fibrinolysis.

Clinical setting for DIC:

(i) Major trauma

(ii) Septicaemia (usually with acidosis)

(iii) Obstetric crises (placental abruption, eclampsia, retained dead foetus)

(iv) Malignancy (acute promyelocytic leukaemia)

Tests for DIC include FBC (with blood film for fragments), platelet count (as part of FBC), prothrombin time (PR), APTT, fibrinogen assay and D-dimers.

Dientamoeba fragilis specimen: faeces in PVA fixative obtainable from lab.

A flagellated amoeba recognised as a cause of acute or recurrent diarrhoea. Most acute cases are self-limiting and do not need treatment.

Laboratory diagnosis is by recognition of the trophozoite in stained films made from faecal material fixed in PVA.

Faecal excretion is erratic and multiple examinations, e.g. three specimens on different days, may be required for detection. There is uncertainty about treatment. Doxycycline 100 mg 12-hourly for 10 days has been used.


Differential white cell count see Blood count

Digoxin specimen: serum

therapeutic range: 1.2�2.6 nmol/L (trough level)

Specimen should be taken at least 6 hours after last dose. Half-life is 36 hours, time to steady state 8 days. Where toxicity is suspected, digoxin administration should cease until the serum level has been measured � the long half-life means the decline to sub-therapeutic levels is slow whereas a move higher into the toxic range can be lethal.

Because digoxin is 85% eliminated by the kidney, renal impairment (as in the elderly) is a potent cause of toxicity. Low K+ and high Ca++ levels potentiate toxicity. Hypothyroidism and some drugs raise digoxin levels.

A source of falsely high digoxin levels is an ill-defined plasma substance termed DLIF (digoxin-like immuno-reactive factor). Levels of DLIF can be up to 0.5 nmol/L in healthy people taking no medication or as high as 3.0 in patients with renal or hepatic failure.

See also Errors: antibody error


Dilantin (phenytoin) specimen: serum

therapeutic range: 40�80 µmol/L (trough level)

Dilantin's unique pharmacokinetics make measurement of serum levels important.

At sub-therapeutic levels, Dilantin is removed by the liver at a rate proportional to serum concentration. Within the therapeutic range, however, degradative enzymes are saturated and serum levels climb quickly. For many patients, symptoms of toxicity appear soon after the upper therapeutic limit is passed. Several common drugs can precipitate toxicity by displacing Dilantin from its protein binding or by inhibiting its breakdown.

see also Anticonvulsants

Diphtheria see Corynebacterium diphtheriae

Diphyllobothrium latum A tapeworm found in the human small intestine where it can live for 20 years and reach 10 metres in length. By competing for vitamin B12 it can cause megaloblastic anaemia. It is acquired by eating larvae in raw fish flesh. Even when fish is cooked adequately, humans may become infected by sampling the flesh during preparation. Distribution is mainly in Scandinavia but also in Japan and the Pacific Coast of the USA. Diagnosis is by finding characteristic eggs or proglottids in faeces. Final control will only occur by prohibiting the discharge of untreated sewage into lakes and streams. Treatment is praziquantel, 10mg/kg as a stat dose.


Direct bilirubin see Bilirubin, conjugated (direct) and unconjugated (indirect) fractions(direct)

Direct Coombs test see Coombs test

Disaccharidases specimen: small bowel mucosal biopsy transported immediately to the laboratory

on ice � do not place on paper.

ref. ranges:

U/glactase 2 - 8maltase 8 - 40sucrase 3 - 18

Clinically, lactose intolerance, which can be secondary to a variety of gastrointestinal disorders, is the most important of the dissacharidase deficiencies.

see Reducing substances in faeces for lactose intolerance in infants

Disseminated intravascular coagulation see DIC (Disseminated intravascular coagulation)


DLE see SLE (systemic lupus erythematosus)

DM see Diabetes mellitus (DM)

DNA antibodies (anti-double-stranded DNA)

specimen: serum interpretation: <1:20 negative 1:20 or 1:40 equivocal >1:80 supports diagnosis of SLE

Anti-ds DNA is positive at 1:80 or higher in 60-80% of SLE. Low titres may be seen in rheumatoid arthritis, autoimmune hepatitis and in other immunological disorders.

DNA, genetic studies see Molecular genetics - genetic studies


DNA, paternity see Paternity testing

Donath-Landsteiner test

Used for the diagnosis of paroxysmal cold haemoglobinuria.

see Cold agglutinins

Dopamine see Catecholamines

Down's syndrome, (trisomy 21) pre-natal testing

Also called Down syndrome


Drug allergy see Penicillin allergy


Anaesthetic allergy

Drug screen – overdose specimen: 30 ml random urine

Overdose screens are usually for persons admitted to hospital. The panel of drugs to be tested will depend on the history and clinical findings.

Drug screen – pre-employment screen and drugs of abuse specimen: 30ml random urine

A common panel includes:

• amphetamines • barbiturates • benzodiazepines • cannabinoids • cocaine • opiates • phencyclidine (angel dust)

Results are reported as +ve or -ve using internationally recognised cut-off limits.

Serum is not used for screening.

If alcohol is required a blood (serum) specimen should be collected to give a quantitative result which will separate the prospective employee who had a health-giving glass of wine the night before from the chronic alcoholic with a sustained high alcohol level.


Pre-employment screens, common for some years in the USA, are being used more often now in New Zealand and in some occupations, for example in public transport, random checks may be used.

When results are to be used medico-legally, there has to be a secure audit trail beginning with direct observation of specimen collection.

Drugs, therapeutic monitoring (TDM)

As a general rule, trough levels are measured, i.e. the low point reached before the next dose is taken. Patients can defer their morning dose, attend the laboratory at 09.00 hrs to have blood off and then take their daily dose after that.

The exception is theophylline where the peak is monitored: the blood specimen should be collected 4 hours after a sustained-release preparation or 2 hours after the shorter-acting 6 hourly preparation.

The half-life (t½) is the time for a serum level to drop by 50%. When a drug is started, or the dosage changed, the time to reach a new steady state = t½ x 5.

Reasons for drug monitoring include:

• check compliance • guide dose adjustment • check for toxicity • monitor interactions if a new drug is added

see also Antiarrhythmic drugs Antidepressant drugs, tricyclic Anticonvulsants


individual drug entries

DVT (deep vein thrombosis) see Venous thromboembolism (VTE)

INR (international normalised ratio)

E

E1 (oestrone) see Oestrogens

E2 see Oestradiol (E2)


E3 see Oestriol (E3)


Ear swabs & infections

Otitis media

It is not possible to sample the middle ear routinely and the flora of the external meatus bears no relation to that behind the drum. Antibacterial treatment is therefore empirical, based on studies which show the role of H.influenzae, Strep. pneumoniae, Moraxella (previously Branhamella) catarrhalis, and Strep. pyogenes. Amoxycillin, cotrimoxazole and amoxycillin-clavulanate provide effective treatment. Cefaclor has insufficient activity against Strep. pneumoniae for it to be recommended in this situation.

Otitis externa

Ear swabs are taken from just inside the external meatus. The commonest pathogens are Staph. aureus and Pseudomonas aeruginosa. H. influenzae and S. pneumoniae are also frequently isolated.

Most cases respond to keeping the ear clean and dry.

% susceptible to topical agents are:

% susceptible to topical agentschloramphenicol neomycin¹ polymyxin²

S. aureus 99 80 0P.aeruginosa 0 0 100

1. Neomycin susceptibility predicts susceptibility to framycetin (Soframycin) and gentamicin.2. Polymyxin susceptibility predicts susceptibility to colistin which is contained in Coly-Mycin S Otic ear drops.


EBV (Epstein-Barr virus) antibody see Infectious mononucleosis

Echinococcus see Hydatids

Echis ratio (ER)

This test is helpful in deciding whether a prolonged PR/INR is due to impaired hepatic protein synthesis or vitamin K deficiency/warfarin. Other conditions such as heparin therapy, severe DIC and congenital factor deficiency may affect the Echis ratio and must be excluded before interpreting results.

PR ER causeprolonged normal vitamin K deficiency/warfarinprolonged prolonged reduced factor synthesis (liver disease)

The test is based on the ability of the Echinus carinatum venom, from the saw-toothed viper, to activate factors II and X.

Echoviruses see Enteroviruses


E. coli (Escherichia coli)

An important member of the normal flora of the intestine and the cause of 80% of urinary tract infections.

% susceptiblenorflox nitrof aug trimeth cotrim amox

E. coli 100 99 96 77 79 44 E. coli can also cause septicaemia or meningitis, particularly in infants.

Enterotoxigenic E. coli causes diarrhoea but this is not detected by routine faecal cultures.

Culture for E.coli 0157/H7, which is associated with haemorrhagic colitis, a severe form of diarrhoea, and with haemolytic-uraemic syndrome, can be arranged on request.

Ectopic ACTH syndrome see Cushing's syndrome

Ectopic pregnancy see hCG (human chorionic gonadotrophin)


EDTA seeTubes for blood collects

Electrolytes specimen: serum

The standard electrolyte group consists of Potassium (K+), serum and Sodium (Na+), serum � see separate entries on these.

Electrophoresis (EPP) of serum proteins specimen: serum

The main indication is suspected myeloma or macroglobulinaemia when investigating unexplained high ESR (above 50), back-pain, unexplained anaemia, suspected malignancy, etc. EPP pattern

The fractions demonstrated by agarose gel electrophoresis are:-


mean concentration(g/L)

albumin (at anodal end of EPP) 42

alpha-1 globulin alpha-1 antitrypsin 3orosomucoid 1alpha lipoprotein (HDL) 0.5

alpha-2 globulin alpha-2 macroglobulin 2.5haptoglobin 1.5ceruloplasmin 0.4

beta globulin beta lipoprotein (LDL) 5transferrin 3complement (mainly C3) 1.5

gamma globulin IgG 7 - 15IgM 0.5 - 2.5IgA 1 - 3

Additional Bands

• Benign or malignant paraproteins (qv) are usually in the gamma zone but some, particularly IgA, may overlie the beta band or occasionally lie between the alpha 2 and beta bands.

• Free light chains (Bence Jones protein) being of relatively low MW are found

mainly in urine but occasionally form a band, usually in the beta-gamma zone, particularly in patients with renal impairment.

• If the specimen is haemolysed, Hb will show as a band between the alpha-2 and beta

• In plasma (as distinct from serum), fibrinogen forms a band between the beta and gamma zones.

• A markedly elevated CRP can sometimes be seen as a weak band in the gamma zone.

• Beta-gamma bridging is sometimes seen in inflammatory conditions.


Abnormal EPP Patterns

• reduced albumin � see Albumin • reduced alpha-1 � see Antitrypsin (alpha-1-antitrypsin - AAT) • increased alpha-1 and/or alpha-2 � usually due to increased acute phase

reactants (qv). • reduced gamma � see Immunoglobulins, IgA, IgG, IgM • diffuse increase in gamma � see Immunoglobulins, IgA, IgG, IgM • nephrotic syndrome pattern � low albumin, increased alpha-2

(macroglobulin), reduced gamma.

Electrophoresis of lipoproteins see Lipoprotein electrophoresis

Electrophoresis of urine specimen: random urine

This is a test for free light chains (Bence Jones protein) in IgG or IgA myeloma and occasionally with IgM-associated malignancies. After concentrating the urine, free light chains show up as a well-defined band in the beta or gamma zone.

In Bence Jones myeloma (10-20% of all myelomas) a heavy band of free light chains in urine is the diagnostic feature, usually with no band on serum EPP.

see also Immunoglobulins, IgA, IgG, IgM : malignant paraproteins

EPP of urine is occasionally used in generalised proteinuria to separate selective (albumin) from non-selective proteinuria.

see Proteins, urine (proteinuria)


Elliptocytosis

Hereditary elliptocytosis, transmitted as an autosomal dominant, is a common disorder characterised by large numbers of elliptical cells in the peripheral blood. Usually it is a chance finding but in 15% there is a mild compensated haemolytic anaemia.

ENA (extractable nuclear antigen) antibodies

specimen: serum

interpretation: results are given as +ve or -ve, not as a titre

Some nuclear antigens can be extracted into solution and patients� serum tested for presence of antibodies against those antigens. ENA screen is used as a follow-up test on positive ANA's or where one of the connective tissue diseases other than rheumatoid arthritis is suspected.


antigen associated disease(with approximate % frequency of antigen)

Sm SLE (20%) - antigen is 99% specific when presentRNP MCTD

autoimmune hepatitisSLE (30%)RA

Ro (SS-A) Sjogren's (90%) usually associated with La (SS-B)SLE (40%)polymyositis (5%)RA (5%)neonatal lupus in pregnancy

La (SS-B) Sjogren's (80%) usually associated with Ro (SS-A)SLE (10%)diffuse scleroderma (5%)neonatal lupus in pregnancy

Scl 70 diffuse scleroderma (50%)CREST (10%)

Jo1 polymyositis (30%) - >95% specific when present

Endolimax nana

A non-pathogenic gut protozoan which does not require treatment.

Endomysial antibodies (EMA) specimen: serum

ref. range: not detected

EMA have very high sensitivity and specificity for untreated coeliac disease and dermatitis herpetiforms.

see Coeliac disease (gluten sensitive enteropathy) for interpretation


Entamoeba coli

A non-pathogenic amoeba of the gut which tends to be acquired in situations where Entamoeba histolytica and Giardia are found. Symptoms of gastrointestinal infection, if present, are likely to be due to the latter organisms.

Does not require treatment.

Entamoeba dispar see Entamoeba histolytica

Entamoeba hartmanni A non-pathogenic gut protozoan which does not require treatment.

Entamoeba histolytica

As far back as the early 1900s it was suspected that there were two "types" of Entamoeba hystolytica, one which causes disease and one which was non-pathogenic. Work over the past 25 years has proven this early suspicion to be true. There are two morphologically indistinguishable Entamoeba species : E. histolytica, the cause of intestinal and extra-intestinal amoebiasis; and E. dispar, its non-invasive relative.


E. histolytica is the causative organism of amoebic dysentery. Clinical infection is due to trophozoites invading the gut wall. The spectrum of disease ranges from mild changes in bowel habit through chronic recurrent diarrhoea to fulminant bloody diarrhoea with invasion of the liver and other sites by trophozoites. Amoebic dysentery is diagnosed by finding highly specific trophozoites which have ingested erythrocytes. This is a rare finding in our laboratory. Where E. histolytica is suspected as a cause of severe dysentery, please consult with the microbiologist to discuss arrangements to allow examination of fresh stool for trophozoites.

Treatment of amoebic dysentery or hepatic abscess is with metronidazole, 400-800mg 8-hourly for 10 days.

Almost all reportings of E. histolytica are based on finding typical cysts. It is not uncommon to find them in the faeces of people who have been to, or have originated from, third world countries and it is likely that a good proportion of these are E. dispar rather than E. histolytica. Treatment is generally not indicated because if the cysts are E. dispar they are not pathogenic and if they are E. histolytica the risk of developing invasive disease during asymptomatic carriage is low. Treatment of cyst carriage is indicated if there is reason to suspect infection with E. histolytica, e.g. high titres of specific antibody, history of close contact with a case of invasive amoebiasis, or an outbreak of amoebiasis (unlikely in New Zealand). Some would treat cysts if the patient was receiving steroids which are a risk factor for amoebiasis.

Treatment of asymptomatic cyst carriage is with:

diloxanide furoate,

or paromomycin,

or iodoquinol

These agents are not registered in New Zealand and can be provided only on a named patient basis.


Enterobacter species

Gram-negative enteric bacilli, part of normal enteric flora, occasionally a cause of urinary tract infection in the community. May cause systemic infection in hospitalised patients. Treatment choice depends on susceptibility results.

Enterobius vermicularis (pinworm)

Common cause of pruritis ani. Spread from person to person by faecal-oral route. Adult worms live attached to the mucosa of the caecum. Gravid females migrate to the anus. The cream coloured adult female worm, approximately 10mm long, lays eggs on the perianal skin. Each female deposits approximately 20,000 eggs on the host, bed clothes and linen. Eggs are infectious shortly after laying, are relatively resistant to drying and remain viable in linen, bedclothes, or house dust for several days. Eggs can be demonstrated using a swab or cellotape imprint. Usually anthelmintics are prescribed on clinical grounds alone, e.g. mebendazole or pyrantel. Many recommend that all family members should be treated simultaneously.

Enterococcus

Previously known as S. faecalis or Group D Streptococcus.

A common cause of urinary tract infections and can be an important pathogen in bacterial endocarditis.

% susceptible in the urinary tractamox-clav amox trim nitrof norflox

Enterococci 99 99 0 99 82


Enteroviruses

A large group of viruses including polio, coxsackie and echoviruses affecting a wide variety of organ systems. Their name is derived from their ability to infect the gut and be shed in faeces.

Identification of the viruses or their antibodies is seldom required in general practice.

Eosinophils specimen : blood (EDTA)

ref. range: 0 � 0.5 x 109/L

Eosinophilia

Eosinophil counts are part of a routine blood count. The common causes of eosinophilia are drug effect, allergy or parasitic infestation of the gut.

The differential diagnosis includes:-

• allergic disorders

• parasitic colonisation � hookworm, filaria, hydatids, toxocara

• drug administration

• skin disease, e.g. eczema, psoriasis, pemphigus

• collagen disorders, especially polyarteritis nodosa

• infections, e.g. TB, scarlet fever

• malignant disease, e.g. lymphoma, Hodgkins disease, ovarian Ca.

• pulmonary eosinophilia


• hypereosinophilic syndrome (a rare myeloproliferative disorder)

Epidermophyton see Dermatophytes

Epilim see Valproic acid (Epilim)

EPP see Electrophoresis (EPP) of serum proteins

Epstein-Barr virus see Infectious mononucleosis

Errors

There is a distinction between errors, which are due to human fallibility, and variance (qv) which is the sum of the unavoidable fluctuations due to biological changes (e.g. diurnal rhythms) and the analytical imprecision of the method.


There are four main sources of error.

• Clerical error This is the commonest error, the hardest to detect and potentially the most serious. It includes mislabelling of specimens, transposition of specimens in an analyser rack, transcription errors when entering data into a computer, and so on. We do our best to devise systems that will avoid these errors but we will never, alas, achieve perfection.

• Specimen collection errors The specimen collection procedure may have failed to pick up the cells or microorganism it was aiming for. The specimen may have deteriorated on standing e.g. microorganisms have died; potassium has leached out of red cells into serum

• Analytical error is where the analyst or reagent manufacturer has made a mistake but in practice this is the least important source of error, thanks to modern technology and use of quality control procedures.

• Antibody error Immunoassays � methods incorporating an antibody to detect the analyte being measured, rather than using chemical reactivity � are used in many of the exciting new assays now available, particularly for hormones, antibodies and drugs. Specificity of the antibody is not always absolute. Anti-digoxin antibodies are an example. The term DLIF (digoxin-like immuno-reactive factor) is used to describe substances found in serum which are identified by the analytical antibody as "digoxin" but which in reality are something else. Thus a "digoxin" level may be measured in a healthy person taking no medication at all. The same antibody error can occur potentially in any method and can be the explanation of a result which is wildly astray as shown by finding a much lower or higher level when repeated in a laboratory using a different method.

Important Rule: "If an abnormal result, or a normal result, does not fit the clinical picture, or if it has important diagnostic, therapeutic, or social consequences, don't act on the result until the test has been repeated on a second specimen." If you suspect an error, please phone us. We can often help � and we can make sure that error doesn't happen again.


Erythrasma

A superficial infection of groin, axillae and toe webs caused by Corynebacterium minutissimum leading to pigmentation of pale skin or depigmentation of dark skin. It may fluoresce coral pink under a Woods lamp and be mistaken for a fungal infection. Treatment is with oral erythromycin. Five days treatment is usually enough but 2-3 weeks may be required.

Erythrocyte = red cell

Erythromycin sensitivity

This is an allergic response caused usually by the estolate of erythromycin. It requires at least 1 week (usually 2 weeks or more) of drug ingestion before the typical cholestatic picture develops with elevation of all liver enzymes but particularly ALP and GGT. Clinically there may be jaundice, abdominal pain, fever and malaise. All resolve when the drug is stopped.

Erythropoietin (EPO) specimen: serum

ref. range: 5-30 mIU/ml

Erythropoietin (EPO), a hormone produced by the kidney in response to low renal pO2, has an important role in the regulation of erythropoiesis.

Measurement of EPO can be used when differentiating primary polycythaemia (low EPO) from secondary polycythaemia (high EPO).


Reduced EPO formation is a feature of the anaemia of chronic renal disease and EPO can be used to treat the anaemia.

Escherichia coli see E. coli (Escherichia coli)

ESR (erythrocyte sedimentation rate) specimen: blood (EDTA)

ref. range:

female malechild 1-10 1-10 1-10adult <50 yrs 1-20 1-15 >50 yrs 1-30 1-20

mm/hr

Levels are higher in pregnancy due to hyperfibrinogenaemia.

The ESR is an antique test that still has a place as a non-specific indicator of inflammatory disease and abnormal protein states.

In an acute illness, the ESR may take a week or more to start to rise and stay elevated for some weeks after its resolution. The CRP (qv) by contrast rises and falls more quickly and is in some ways a better marker for acute inflammation.

Interpretation


• ESR within the reference range A "normal" ESR never excludes inflammatory disease but it makes it less likely.

• ESR 20 - 50 Values in this range may have an obvious explanation but sometimes, particularly in the elderly, they persist for no obvious reason. In the absence of any other leads, investigation need not be too intensive. Pregnancy elevations are usually in this range.

• ESR 50-100 These usually have an explanation and should be pursued.

• ESR >100 The "3-figure ESR" nearly always indicates serious disease such as a serious infection, malignant paraproteinaemia or connective tissue disease.

Baseline investigations for a high ESR would include all those relating to serious acute and chronic infections, serum and urine protein electrophoresis, immunoglobulins, ANA, rheumatoid factor.

Essential thrombocythaemia Essential thrombocythaemia is a myeloproliferative disorder characterised by a sustained increase in the platelet count, particularly above 600 x 109/L.

Clinical features include splenomegaly, an increase in thrombotic risk and bleeding of varying severity. Bone marrow biopsy and elevated NAP score are useful in


diagnosis. Treatment is aimed at reducing the platelet count. Therapy at counts which are only modestly increased is controversial.

Estradiol/Estriol/Estrogens see Oestradiol (E2) etc.

Ethanol (ethyl alcohol) see Alcohol, ethyl (ethanol)

Ethosuximide (Zarontin) see Anticonvulsants

Euthyroid hyperthyroxinaemia see Thyroid disease � diagnosis and monitoring

Exposure to blood and body fluids see Needlestick injuries


Extended GTT see GTT

Extractable nuclear antigens see ENA (extractable nuclear antigen) antibodies

Eye swabs

If the eye is moist, use a dry swab; if the eye is dry, moisten the swab in transport medium. After pulling the lower lid down roll the swab across the inner part of the lower lid. If there is pus in the corner of the eye, get some of this onto the swab as well.

In neonates, conjunctivitis can be due to gonococci or Chlamydia trachomatis transmitted from mother to baby during birth. When testing for Chlamydia remove any purulent exudate before collecting conjunctival epithelial cells by rubbing the small Chlamydia swab over the everted palpebral conjuctiva.

Bacterial conjunctivitis outside the neonatal period is most commonly caused by Staph. aureus, H. influenzae or Strep. pneumoniae and usually resolves spontaneously or in response to topical eye drops or ointment. Occasionally unusual bacteria are found. A negative bacterial culture usually indicates a viral or allergic conjunctivitis.


% susceptiblechloramphenicol neomycin¹ fucidin polymyxin B tetracycline

S. aureus 98 94 99 0 97H. influenzae 100 100 0 100 99S. pneumoniae 100 0 — 0 76

1. Neomycin susceptibility predicts susceptibility to framycetin (Soframycin) and gentamicin.

F

Factor VIII assays see von Willebrand's disease (vWD)

Factor V Leiden (FVQ506)

The commonest of the inherited causes of hypercoagulability, first recognised in 1993, is a mutation of the Factor V gene known as Factor V Leiden. Normal Factor V, which promotes normal clotting, is inhibited physiologically by Activated Protein C. Factor V Leiden is abnormally resistant to this inhibitory action and the presence of Factor V Leiden is detected by the APCr test.


Factor V Leiden occurs in 3-7% of Caucasians and is a factor in 20-40% of cases of venous thromboembolism (VTE). Risk of VTE is increased 5-10 times in heterozygotes compared with normal people and 50-100 times in homozygotes. Addition of oral contraceptives increases the risk a further 3-5 times in heterozygous individuals.

see Hypercoagulability

Activated protein C resistance (APCr)

Factor XII

Deficiency of Factor XII is a common cause of prolongation of the APTT.

Mild Factor XII deficiency causes a mild prolongation of the APTT. A significant prolongation of the APTT (e.g. >80 seconds) which corrects with the 1+1 test and which is not associated with bleeding symptoms is usually due to more marked Factor XII deficiency but even low levels are of no clinical significance.

see APTT (activated partial thromboplastin time)

Faecal fat

specimen: faeces collected over a 3-day period into a container supplied by the laboratory and stored in the refrigerator during collection. Extraneous material such as toilet paper, plastic bags or nappies, must be excluded. The patient should be eating 70-100g fat per day for at least three days


prior to and during collection, i.e. not on a fat-reduced diet. Laxatives or cholestyramine interfere with the test.

ref. range:

<1 yr 1.5g/day1-10 yrs <3g/day>10 yrs <5g/day

1g = 3.5 mmol Indications

• for documenting steatorrhoea • for monitoring treatment in patients with known steatorrhoea

This is an unpleasant test for both patient and laboratory and should not be used as a screening test in patients with chronic diarrhoea or other non-specific gastrointestinal symptoms.

Steatorrhoea should be suspected when stools are pale, loose, bulky and greasy. It will seldom be found in formed brown stools. In this laboratory, the mean weight of normal 3-day faecal collects is 350g compared with a mean of 940g for those with steatorrhoea (>5g fat/day).

see also Malabsorption.

Faeces, for culture and microscopy

specimen: 1-3 random fresh faeces collected into small clean jars, each of which should be delivered to the lab as soon as possible, preferably within 4 hours.

We have recently analysed our results for patients who have had three specimens sent for bacterial culture for enteric pathogens:


specimen 1 detected 85% of positives

specimen 1 & 2 detected 95% of positives

specimen 1,2 & 3 detected 100% of positives

Therefore a single specimen detects the majority of positives. Three specimens may be requested in chronic intermittent diarrhoeas or in food handlers where it is essential they be established as being free of infection. The three specimens should be collected on three different days and each taken to the lab on the day of collection. Routine examination includes culture and examination of a wet film for red or white blood cells.

Culture will detect Campylobacter, Salmonella, Shigella, Yersinia, Aeromonas, and Pleisomonas. If infection with a Vibrio species is suspected this should be indicated on the form so special media will be inoculated.

Rotavirus is looked for when the patient is age 5 or less.

Examination for Giardia antigen, or of a faecal concentrate for ova and parasites, is performed only when specifically asked for on the request form.

Faeces for occult blood specimen: faecal smears on reagent cards

Three specimens are collected on 3 separate days and either 1 or 2 smears (from different parts of the specimen) taken from each. They remain stable for up to a week.

Indications


When done properly, a positive result (even one) increases likelihood of gastrointestinal blood loss, especially from lower bowel.

However, because of low sensitivity for detecting small, often intermittent bleeding, a negative result does not exclude GI blood loss as from a tumour. Further evaluation (e.g. colonoscopy) is still therefore indicated in at-risk patients with unexplained iron deficiency.

Types of test/dietary advice

Non-specific guaiac tests These, the most commonly used tests, detect the peroxidase activity of haem whether of human or animal origin.

They can give false positives with high meat diets, peroxidase-containing foods such as horse-radish or turnip, or sometimes with iron supplements. Gastric irritants such as NSAIDSs can give positives because of the minor bleeding they induce.

High dose vitamin C or E supplements can give false negatives.

Specific immunochemical tests Most of these detect intact human Hb but others are based on human haem, porphyrin or even albumin. Although these tests avoid dietary false positives, there is still the large problem of positives due to minor benign bleeding.

Faeces for ova and parasites specimen: 1-3 random faeces samples

The ova and parasites box must be ticked if these are required in addition to faecal culture.


Where Giardia (qv) is suspected, the antigen test is more sensitive than the standard parasite screen. The antigen test is requested by ticking the Giardia box.

Fanconi syndrome

A generalised disorder of renal tubular function characterised by acidosis, amino-aciduria and glycosuria. It can be a primary defect but is more often secondary to some other metabolic condition or to nephrotoxins or drugs.

Fat, faecal see Faecal fat

FBC (full blood count) see Blood count

FDP (fibrin degradation products) do test for D-dimers

Fe see Iron


Ferritin

specimen: serum

ref. range:

Age µg/L

<6 mths 50-4006 mths-15 yrs 12-140adult female 20-160adult male 20-250

Low levels

Ferritin is a measure of total body iron stores and levels below 12 indicate seriously deficient or absent stores. Results between 12 and 20 suggest reduced stores. Iron stores are often marginal in infancy, adolescence and in women during their child-bearing years, especially if diet is deficient. At other times they should prompt a search for sites of blood loss.

see Iron deficiency for more detailed discussion.

In the presence of inflammation, which elevates ferritins, an iron-deficient person may have a normal result despite their lack of iron.

High levels

• haemochromatosis � (qv)

• liver disease � in viral hepatitis the ferritin can rise above 4000.

• alcohol

• chronic inflammation � connective tissue diseases, bacterial infections

• malignancy, particularly leukaemias, lymphomas and myeloma


• thyrotoxicosis

• excessive parenteral iron therapy

• multiple blood transfusions in refractory anaemias

A raised ferritin is not uncommonly found with no immediately obvious explanation. If the fasting iron saturation is above 50% the HFE gene should be tested as a marker for haemochromatosis.

If no explanation is found, ferritin should be checked at least annually with appropriate follow-up of clinical developments.

Fetal see Foetal Hb

Fetoprotein see AFP (alpha foetoprotein)

Fibrin degradation products do test for D-dimers

Fibrinogen specimen: plasma (citrate)



Fibrinogen is reduced in:

• afibrinogenaemia (total absence of fibrinogen)

• hypofibrinogenaemia (decreased synthesis of fibrinogen)

• dysfibrinogenaemia (structural abnormality of the fibrinogen molecule) - Fibrinogen is increased in inflammatory conditions.

It is measured as part of the basic haemostasis screen.

Filariasis specimen: whole blood (EDTA)

Filariasis occurs in Africa, Latin America, Asia and the Pacific Islands where the most common cause is Wuchereria bancrofti. Diagnosis is by finding microfilaria in peripheral blood. An eosinophilia may be the only evidence of filarial infestation. Lymphatic filariasis occurs when host inflammation and fibrosis lead to lymphatic occlusion and in patients heavily and repeatedly infected, elephantiasis may develop. Bacterial cellulitis contributes to tissue damage. The syndrome of tropical eosinophilia is an extreme reaction to filariasis.

Treatment with diethyl carbamazine or ivermectin clears microfilaria from the blood. Dying microfilaria can stimulate a severe allergic reaction requiring treatment.

Fine needle aspirate (FNA)


Separate instructions for FNAs are available on request for those using this technique. A service is also provided by our pathologists.

Flavobacterium

see Chryseobacterium

Fluoride tube for glucose see Tubes for blood collects

Flushing attacks see HIAA (5-hydroxy indole acetic acid)

FNA see Fine needle aspirate (FNA)

Foetal Hb see Hb ( haemoglobin)


Foetoprotein see AFP (alpha foetoprotein)

Folate (folic acid), serum specimen: serum

ref. range: 8.0-35.0 nmol/L

6.0-8.0 nmol/L: borderline low

Although the terms folate and folic acid are often used interchangeably, another usage is to apply folate to the serum analyte and naturally-occurring vitamin found particularly in green vegetables, while using folic acid to refer to the synthetic chemical used in vitamin supplements.

Folate deficiency is associated with three important disorders.

• macrocytic megaloblastic anaemia As with vitamin B12 deficiency, the correlation between serum folate level and peripheral blood findings is not close.

• birth defects, particularly neural tube defects Studies have shown dramatic reduction in birth defects in women taking 400µg folic acid daily, commencing prior to conception.

• cardiovascular disease The evidence is circumstantial only and concerns the plasma homocysteine levels which appear to be a graded independent risk factor for cardiovascular disease. When plasma folate is maintained consistently above 15 nmol/L, using a supplement of 400µg folic acid daily, plasma homocysteine falls to a low


plateau.

Although definitive studies are not available at the time of writing (are under way), it seems at least possible that a daily supplement of 400µg folic acid could be beneficial and that the low end of the 8.0-35.0 nmol/L reference range is not as desirable as the mid-zone.

Causes of low serum folate

• Inadequate diet � the commonest cause. Folate comes particularly from green vegetables and is destroyed by cooking. Deficiency is associated with old age, poverty, alcoholism, anorexia

• Malabsorption � coeliac disease, tropical sprue, giardiasis

• Drugs � anticonvulsants, pyrimethamine, methotrexate and others

High folate levels are due to vitamin supplements or a recent meal high in folate.

Total body stores in a healthy individual approximate 10mg, enough to last about 6 months if all dietary folate is removed. Recommencement of folate intake restores serum levels in a few days but replenishment and maintenance of body stores requires sustained intake.

see also Macrocytosis

Folate, red cell specimen: whole blood (EDTA)

ref. range: 400�1800 nmol/L


Red cell folate is a better indicator of tissue stores than serum folate, which is more labile. The red cell folate method has precision problems however and is more expensive. In practice it is not always used despite its theoretical superiority.

Interrelationship between B12 and folate deficiencies:

1° deficiency Serum B12 Serum folate Red cell folate

B12 ↓↓ n↑ n↓folate n↓ ↓↓ ↓

Follicle stimulating hormone see FSH (follicle stimulating hormone) and LH (luteinising hormone)

Food allergy

True IgE-mediated, immediate-response, food allergy affects about 5% of children and 1% of adults.

In children, milk, eggs and peanuts are important. In adults, peanuts, fish, shellfish and fruit.

Adverse reactions to food are more often non-allergic, e.g.

• transient lactase deficiency in infants causing milk intolerance

• tyramine in cheese or red wine causing headaches

• monosodium glutamate in Asian cooking causing abdominal symptoms

• metabisulphate added as preservative to dried foods or white wine


Diagnosis requires a careful history, trial of withdrawal of the suspected food and, in selected cases, food challenge - supervised if past reactions have been serious.

Skin tests and RAST tests are less helpful in food allergy than in allergy caused by inhaled allergens and can give both false negatives and false positives. Peanuts, cows milk and eggs are included in most standard batteries of skin tests. Specificity is not particularly high but a -ve test makes allergy less likely and a +ve test, particularly in the context of a positive history, makes the diagnosis more likely. Testing the patient with an ill-defined history of vague complaints against a wide range of foods will seldom be productive.

Free T3 see T3, free (tri-iodothyronine)

Free T4 see T4, free (thyroxine)

Free testosterone see Testosterone

Frozen section/rapid smears by arrangement with Histology Department.


Fructosamine specimen: serum

ref. range: 190-290 µmol/L

Fructosamine is glycated albumin and gives a measure of the mean glucose level over the preceding 1�3 weeks in diabetes. For the laboratory, fructosamine is a cheaper test than HbA1c but it has major disadvantages.

• in obese patients, who make up the bulk of the Type 2 diabetic population, it is falsely low.

• it is lowered in any condition where there is increased albumin turnover, most notably by the proteinuria of diabetic nephropathy.

• its correlation with HbA1c is not good.

• �diabetologists don't like it.

Should it be used at all? Provided an HbA1c is available, fructosamine should probably be used only in patients with increased Hb turnover as in haemolysis or chronic blood loss; or perhaps during pregnancy when rapid improvements in glycaemic control are being sought.

Indicative levels of control in diabetes:

around 300 is the target value280 - 330 good control330 - 380 fair control380 - 450 bad control>450 requires urgent attention

In pregnancy there is a fall in fructosamine values to within a range of about 150 - 260.


see also HbA1c (glycated Hb)

FSH (follicle stimulating hormone) and LH (luteinising hormone) specimen: serum

ref. ranges:

FSH LHadult femalefollicular and luteal phases 1-8 IU/L 2-15 IU/Lmid-cycle ovulatory peak 6-26 20-120post-menopausal 18-120 15-100pregnancy/oral contraceptives <1 <2adult male 1-9 2-12

Physiological actions The complex cyclical variations in FSH, LH, oestradiol and progesterone in the menstrual cycle are shown in the diagram.

Specimens are collected outside the mid-cycle peak except when timing ovulation. Release of both hormones is episodic and can lead to biological variation throughout the day.

In the male, FSH stimulates spermatogenesis whereas LH (also known as ICSH), stimulates interstitial cells to release testosterone.

Applications

• Identifying the menopause � the FSH rises from a base-line of less than 8 to above 20. FSH rises relatively more than LH. see also Menopause.

• Ovarian or testicular failure � both FSH and LH rise to menopausal levels. Gonadal failure can be primary as in agenesis, dysgenesis, Klinefelter's or


Turners syndromes. Or it can be secondary as in premature menopause, oophorectomy, or testicular damage.

• Identifying day of ovulation in fertility control.

• Hypopituitarism � LH and FSH are not usually undetectable in hypopituitarism but low or inappropriately normal values in patients with low oestradiol (women) or low testosterone (men) are suggestive. Mid-range or high values can help exclude hyopituitarism.

• Polycystic ovary syndrome (qv) � LH is often raised relative to FSH with an LH/FSH ratio >2.


These cyclical changes will not, of course, be found in women on oral contraceptives which suppress LH and FSH below the reference range.

FTA (fluorescent treponemal antibody)

specimen: serum

A positive FTA indicates past or present treponemal infection. It does not distinguish between syphilis and yaws. The FTA stays positive life-long.

see also Treponemal serology (STS, serological tests for syphilis)

Full blood count (FBC) see Blood count

Fusobacterium

An anaerobic gram-negative bacillus, found in situations predisposing to anaerobic (qv) infection, e.g. following a break in the integrity of mucosal surfaces. Fusobacterium necrophorum can cause local disease of the oropharynx complicated by septic thrombophlebitis and metastatic abscesses. Usually susceptible to penicillin as well as other ß-lactam agents. Also susceptible to metronidazole.


G

G-6-PD (glucose-6-phosphate dehydrogenase)

specimen: blood (heparin or EDTA)

ref. range: 4.6 - 13.5 EU/g Hb

Quantitative assay is done if the screen test is abnormal.

G-6-PD deficiency is a cause of drug-induced haemolytic anaemia, commonest drugs being nitrofurantoin, sulphonamides, nalidixic acid, anti-malarials, sulphones. Deficiency occurs particularly in Mediterranean peoples, black Africans and some Asiatics.

GAD autoantibodies

see Diabetes autoantibodies


Galactorrhoea

Most patients are women but occasionally galactorrhoea is found in men. Causes are:

• Hyperprolactinaemia. This is commonly, but not invariably, associated with galactorrhoea. There may or may not be a pituitary tumour. Elevations of prolactin (qv) can be minimal and intermittent.

• Hypothyroidism and hyperthyroidism.

• Drugs � phenothiazines, benzodiazepines, tricyclics, methyldopa, butyrophenones, metoclopramide, H2 receptor antagonists, digoxin, spironolactone, post-oral-contraceptive.

Galactosaemia A screen test for galactosaemia is part of the standard neonatal screen in the first week of life.

see Neonatal screening

Gallstones

These consist mainly of cholesterol except in chronic haemolysis when pigment (bilirubin) stones may be formed. Analysis of a stone is of interest only when haemolysis is suspected or when an unidentified.object ? gallstone, is found in faeces.


Gamma globulins see Immunoglobulins, IgA, IgG, IgM Electrophoresis (EPP) of serum proteins

Gamma glutamyl transpeptidase see GGT (gamma glutamyl transpeptidase)

Gardnerella vaginalis

Formerly known as Haemophilus vaginalis and Corynebacterium vaginalis.

A common bacterial isolate from the vagina. It may be present in up to 30% of healthy women. When found in association with "non-specific vaginosis", treatment with metronidazole or tinidazole will eliminate odour and discharge though there is a tendency to recurrence requiring repeat treatment. see also Vaginal discharge.

Gastric antibodies see Intrinsic factor antibodies and parietal cell antibodies


Gastric and oesophageal brushings/washings for cytology

Smears should be made from brushes and fixed in Cytofix immediately. Washings should be submitted to the laboratory as soon as possible.

Gastrin specimen: serum, separated and frozen immediately

ref. range: 0-75 pmol/L, fasting

Gastrin, released from the gastric mucosa, is a potent stimulant of gastric acid secretion.

Gastrin measurements are used in the diagnosis of pancreatic gastrinomas associated with severe peptic ulceration in the Zollinger-Ellison syndrome in which there is marked hypersecretion of gastric acid.

Vagotomy, non-fasting state, renal failure, or the gastric acid hyposecretion due to pernicious anaemia and chronic atrophic gastritis, are associated with an increase in gastrin levels.

GDM see Gestational diabetes mellitus (GDM)


Genetic studies see Cytogenetics Molecular genetics - genetic studies

Genotype The genetic constitution of an individual with definition of both dominant and recessive genes in a gene pair. By contrast the phenotype defines only the dominant member. In relation to rhesus blood grouping the phenotype CDE could have, for example, the genotype CDE/CDE or CDe/cdE.

Gentamicin

see Antibiotics, serum levels

Gestational diabetes mellitus (GDM)

GDM is a form of glucose intolerance that develops during the 2nd half of pregnancy and disappears after parturition.

It is associated with increased foetal risk which is reduced if the GDM is treated successfully with diet or, in the few where hyperglycaemia persists, with insulin. A mother with GDM is at increased risk for developing diabetes in later life.

Polycose screen test for GDM


Screening at 24-28 weeks is currently recommended for all pregnant women, though clearly at-risk patients, e.g. previous GDM, can be evaluated earlier, even before conception.

The test is usually done in the morning. No booking is required and the patient does not need to fast before the tests. A suspension of 50grams of polycose is given and a single blood collected 1 hour later. If the glucose is above 7.8 mmol/L, a 2-hour GTT is ordered as the definitive test.

If the post-polycose glucose is less than 7.8 but risk factors are present � obesity, family history of diabetes, history of GDM, macrosomia, intrauterine or neonatal death � another polycose screen test or a GTT should be considered at 32-34 weeks to check whether glucose tolerance has deteriorated.

Diagnostic GTT criteria for GDM

GDM is present if:

fasting glucose ≥ 5.5 mmol/L or 2-hour glucose ≥ 9.0 mmol/L

GGT (gamma glutamyl transpeptidase)

specimen: serum ref. range: female 0-50 U/L male 0-60 U/L

GGT is found almost entirely in the liver. It is elevated particularly in cholestatic disorders, by alcohol, and also as an effect of some drugs, notably anticonvulsants.


GGT is the enzyme most reliably raised by excessive alcohol, typically in the range 60-200 but occasionally >1000. 30% of heavy drinkers have normal levels. After a weekend binge, levels rise up to 100% over 3 days. If the cause of an elevated GGT is uncertain, total abstinence from alcohol with weekly GGT estimations over a 4-week period may provide the answer.

see also Liver enzymes

GH see Growth hormone (HGH, somatotropin)

Giardia specimen: 1-3 random faeces samples.

Giardia lamblia is a protozoan infesting the upper small bowel where it can cause acute or chronic diarrhoea and sometimes fat and vitamin malabsorption.

It is now the commonest cause of water-borne diarrhoea in the world with vast reservoirs in humans and wild and domestic animals and in rivers and water supplies. Although more common in third world countries with poor sanitation it is increasingly being found in developed countries including New Zealand. At this laboratory it is the third commonest faecal pathogen after Campylobacter and Salmonella.

It is commonly taught that three stool specimens are required to detect intestinal parasites such as Giardia but several studies have shown that >85% of cases are


detected on the first specimen. When evaluating chronic or relapsing diarrhoea it may be necessary to send up to three specimens for testing.

The two commonly-used tests for Giardia:

• Detection of Giardia antigen in faeces using an Elisa method.

• Microscopy for cysts in faecal concentrate. Occasionally trophozoites are seen in acute infections.

The antigen method is the more sensitive.

Treatment with tinidazole or metronidazole is usually effective but may need to be repeated.

Gilbert's syndrome

This common, harmless, inherited condition, in which the liver has reduced ability to conjugate bilirubin, was first described in 1901 by the Frenchman Gilbert whose name is usually, though not always, pronounced in the English fashion.

It affects somewhere between 2 and 10% of the male population depending whether the cut-off is taken as 25 or 20 µmol/L. The male/female ratio is about 4:1.

Because a genetic test is not available, diagnosis is based on exclusion.

Features are:

• elevation of bilirubin is the only laboratory abnormality and the level seldom exceeds 80 µg/L.

• liver enzymes are normal.


• the bilirubin is unconjugated.

• there is no evidence of haemolysis as measured by reticulocytes and haptoglobins.

• the bilirubin level fluctuates; the condition is often first detected in the 2nd-3rd decade.

• fasting, dehydration, fever, sea-sickness, intercurrent illnesses, can all cause the bilirubin to rise, sometimes to the point where it becomes visible as jaundice. At this point the patient may note malaise, blaming it on the Gilbert's rather than the precipitating factors.

Glandular fever syndrome This syndrome, which includes atypical lymphocytosis, lymphadenopathy, pharyngitis and malaise, is due mainly to infectious mononucleosis, toxoplasma or CMV � see entries under these headings.

Gliadin (gluten) antibodies (AGA) specimen: serum

-ve borderline +ve

IgA AGA <30 30-50 >50IgG AGA <40 40-60 >60

Anti-gliadin antibodies (AGA) have a high degree of sensitivity and specificity for untreated coeliac disease and dermatitis herpetiforms. see Coeliac disease (gluten sensitive enteropathy) for more detail


Globulins, total specimen: serum

ref. range: 18-34 g/L

total globulins = total proteins � albumin

see Electrophoresis (EPP) of serum proteins

Immunoglobulins, IgA, IgG, IgM

Proteins, total, serum

Glucose specimen : plasma (fluoride)

ref. range :

Age (yrs) mmol/L

fasting glucose 3.5-6.0random glucose 0-1 2.0-6.0

>1yr 3.5-7.0 If the specimen is collected in a plain tube the glucose level will tend to be low by an unpredictable amount because red cells consume glucose causing the serum level to fall at a rate of 0.1-0.5 mmol/L/hr. Fluoride prevents this glycolysis.

see also Diabetes mellitus (DM)

Glucose tolerance test (GTT)

Hypoglycaemia

Polycose screen test for gestational diabetes (GDM)


Glucose tolerance test (GTT) Indications

The GTT is the traditional test for the diagnosis of border-line diabetes mellitus.

For the patient who does not want to go through the 2-hour GTT, an alternative, recommended by the American Diabetes Association in 1997, is to measure two fasting glucoses on two separate days.

Contraindications

A GTT is unnecessary in a person who has symptoms of diabetes (thirst, polyuria, tiredness), and random glucose levels >11.1. An HbA1c above 6% further confirms the diagnosis in this situation and gives an indication of mean glucose level.

The GTT is not a useful test for monitoring treatment and is never used in a diabetic on oral hypoglycaemics or insulin.

It should not be performed during intercurrent illness or periods of stress or in a person on a low carbohydrate diet, all of which elevate glucose levels above their usual values.

Test protocol

The patient makes an appointment and fasts overnight (10-14 hrs). Excessive fasting worsens tolerance.

The glucose load is given in the form of polycose, a relatively non-emetic polymer of glucose.

2-hour test for suspected diabetes or GDM


Dose for adult: 75g

Dose for child: 1.75g/kg body-weight

Bloods are collected fasting and at 1 and 2 hours. The patient stays in the collection room throughout and should not smoke.

Urines are no longer collected except where renal glycosuria is a possibility.

4½ hr test for reactive hypoglycaemia This is discussed in more detail under hypoglycaemia. It is not generally regarded as a useful test but if done, the dose is 100g and bloods are collected at ½-hrly or hrly intervals.

Interpretation

The current (2000) criteria for plasma measurements are:

Fasting 2 hrnormal non-pregnant <6.0 <7.8diabetes — 1 or both of >7.0 >11.1IGT 7.8-11.0IFG 6.1-6.9normal pregnant <5.5 <9.0GDM — 1 or both of >5.5 > 9.0

IGT = impaired glucose tolerance

IFG = impaired fasting glucose (or glycaemia)

GDM = gestational diabetes mellitus

The ADA (American Diabetes Association) has recommended that the GTT be replaced by 2 fasting glucose levels or by random glucose levels.

Diabetes is then diagnosed by


2 fasting glucoses >7.0 mmol/L 2 random glucoses >11.1 mmol/L 1 fasting glucose >7.0 and 1 random >11.1

Subsequent analyses have shown that screening based on 2 fasting glucose levels will give a significantly lower diabetic prevalence than when the 2 hr GTT is used, the 2 hr level >11.1 being a more sensitive criterion than the fasting level of 7.0.

WHO will be making its definitive recommendation on the use of the GTT in 2000 but meanwhile the GTT retains its position as an accepted diagnostic measure for borderline diabetes.

When diabetic symptoms (thirst, polyuria, weight loss) are present, a single random glucose >11.1 establishes the diagnosis.

As with any biological test, glucose tolerance varies from week to week and month to month and any result in the region of a cut-off limit can switch back and forth between normal, impaired and diabetic under the influence of stress, illness, change of diet, or simply unexplained variance.

Lag storage curve has a 1-hour glucose peak in the 11-15 mmol/L range, then returns to normal at 2 hours. This is seen post-gastrectomy, and sometimes in normal people, when a carbohydrate load rapidly reaches the small intestine and is absorbed before insulin action has time to bring down the glucose peak.

Glucose, urine see Glycosuria


Gluten see Gliadin (gluten) antibodies (AGA) and Coeliac disease (gluten sensitive

enteropathy)

Glycated Hb see HbA1c (glycated Hb)

Glycosuria Glucose appears in the urine when the renal threshold has been exceeded; this typically being at a blood glucose level around 11mmol/L.

With advancing age, or renal impairment, the renal threshold rises so that some diabetics have glucose-free urine even with blood glucose levels in the 12-15 mmol/L range.

Glycosuria is found in:

• Diabetes mellitus � once the renal threshold is exceeded.

• Renal glycosuria � in which the individual has a lowered renal threshold. The GTT is entirely normal but urine specimens collected during the test show glucose. The patient who is proven to have this uncommon condition can be reassured that it is of no clinical significance and is unrelated to diabetes.

• In pregnancy � renal glycosuria is common in healthy non-diabetic women during pregnancy, beginning during the first trimester and disappearing within a week of delivery. A feature of this glycosuria is its variability from day to


day, throughout the course of the pregnancy and even during the course of a day.

Uses of urine glucose tests

• As a side-room test for suspected diabetes when a blood test is not available.

• As a home test for children whose parents worry about diabetes but don't want blood tests.

Urine glucose tests are not used for

• adult diabetic screening

• screening in pregnancy

• monitoring known diabetes

Gonadotropins

see FSH (follicle stimulating hormone) and LH (luteinising hormone) LH (luteinising hormone) hCG (human chorionic gonadotrophin)

Gonorrhoea see Neisseria


Gout see Urate, serum

GPH syndrome = gestational proteinuria and hypertension

GPT see ALT (alaninine transaminase or amino transferase)

Gram stain

The gram stain, described as the single most useful procedure in diagnostic microbiology, was perfected by the Danish microbiologist Christian Gram in 1884. When a microbiological specimen reaches the laboratory there are typically two initial procedures.

• Gram stain of the specimen smeared on a slide to determine numbers of bacteria, whether cocci or bacilli and whether gram-negative or gram-positive. In a case of meningitis for example the gram stain gives a presumptive diagnosis and dictates initial antibiotic treatment.

• The specimen is cultured on a microbiological plate and the colonies gram-stained next day.

Some examples:

gram-positive organisms cocci Staphylococcus


Streptococcus bacilli Corynebacterium gram-negative organisms cocci Neisseria bacilli enteric bacteria: Escherichia, Salmonella, Shigella,

Enterobacter, Klebsiella, Serratia, Proteus, Citrobacter,Yersinia

Graves disease

see Thyroid disease � diagnosis and monitoring

Thyroid antibodies

Group and hold see Crossmatch

Growth hormone (HGH, somatotropin)

specimen: serum ref. range: There is no defined range for random HGH which can vary between 0

and 24 µg/L in healthy people. Suppression or stimulation tests are used in preference to random HGH.

elevated levels � pituitary gigantism � acromegaly


� stress, exercise � insulin-induced hypoglycaemia - used in stimulation tests for dwarfism or hypopituitarism low levels � pituitary dwarfism � hypopituitarism � glucose infusion - used in suppression tests for gigantism or acromegaly.

GTT see Glucose tolerance test (GTT)

Guthrie card see Neonatal screening

Gynaecomastia Transient gynaecomastia is normal in the newborn and in adolescence and minor degrees of persistent gynaecomastia are common in the elderly male as testosterone levels decline with an increase in the oestrogen/testosterone ratio.

The causes of more troublesome and progressive breast enlargement include:

� drugs - oestrogens - spironolactone - digoxin - cimetidine - tricyclics - diazepam - methyldopa - anti-androgens


� hypogonadism � check LH, FSH, testosterone � liver disease � thyrotoxicosis � feminising tumours � Klinefelter's syndrome

H

Haematocrit (PCV) see Blood count

Haematuria see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections)

Haemochromatosis


Haemochromatosis is a condition of iron overload which is usually sub-clinical but which in some patients causes systemic disease due to parenchymal tissue damage.

In its common hereditary form, the diagnosis of haemochromatosis is being made with increasing frequency because of the ready availability of tests for ferritin, iron and iron saturation, and, recently, the HFE gene.

Iron overload can also be acquired due to repeated transfusions for refractory anaemia or to inappropriate parenteral iron over a long period of time.

Hereditary haemochromatosis (HH)

In HH the iron overload is due to excessive absorption which steadily increases the total body mass of iron throughout life. Women are protected during child-bearing years by menstrual loss of iron.

HH is carried on a recessive gene with the remarkably high prevalence of 1:10 in the general population for the heterozygous (carrier) state and 1:400 for the homozygous (affected) state.

In 1996 the HFE gene, also known as the cys282 tyr mutation, was identified as a marker for at least 90% of HH.

Heterozygotes may have mild or moderate elevations of ferritin and iron but will not develop clinical disease.

Homozygotes will not always develop disease but because their risk is so much higher, they are treated by venesection to reduce body iron, as measured by ferritin, to normal levels.

Clinically HH is characterised by:


• lethargy, skin pigmentation, reduced sweating • hepatic damage: elevated enzymes, cirrhosis, hepatocellular carcinoma • endocrine damage: diabetes, hypogonadism. loss of libido, amenorrhoea,

hypopituitarism, hypothyroidism • arthropathy • myocardial damage: congestive cardiac failure

Diagnosis

HH is suspected when iron saturation is consistently above 55% and ferritin above 400 µg/L.

The HFE gene should be tested for and if present the test will show whether the patient is a hetero- or homo-zygote.

Homozygotes should be further tested for tissue damage by measuring glucose, liver enzymes, TSH, and LH, FSH and testosterone if hypogonadism is suspected.

Before the HFE test became available, a liver biopsy was taken to measure liver iron content and also look for cirrhosis. The hepatic iron index is an expression of liver iron that compensates for the normal increase in iron that occurs with age. An iron index >2.0 µmol iron/ g liver/year of age is indicative of HH. Liver biopsy is seldom performed if the ferritin is <1000 µg/l, liver enzymes are normal and there is no hepatomegaly. Hepatic fibrosis is rare when these criteria are met. Liver biopsy may still have a place where clinical suspicion of haemochromatosis is strong but HFE negative.

Monitoring treatment Venesection is performed at weekly intervals until ferritin is below 100-200 µg/L and then frequently enough to hold the ferritin at this level.

Screening relatives of a proband


Iron, iron saturation and ferritin should be measured in siblings of whom, statistically, 1:4 will be homozygous. All of the children of a homozygote will be heterozygote carriers and if the other parent carries the gene, statistically half of the children will be homozygotes.

Haemoglobin whole blood concentration (Hb) see Blood count

Haemoglobin electrophoresis (Hb EPP) specimen: whole blood (EDTA)

Hb EPP detects abnormal and unstable haemoglobins and gives an indication whether HbA2 or HbF are increased.

Haemoglobin pigments specimen: whole blood (heparin or EDTA)

This term usually refers to metHb and sulphHb which can be found following exposure to some drugs, notably phenacetin, sulphonamides, sulphones, antimalarials; and to some occupational and household chemicals.

When metHb and/or sulphHb exceed 15% of total Hb, the patient appears cyanosed.


Haemoglobinopathy screen

The screen consists of: Hb electrophoresis HbA2 quantitation HbF quantitation HbH body stain Hb stability test Indications

• Suspected thalassaemia (qv) or haemoglobinopathy - hypochromic microcytic anaemia in the absence of iron deficiency or chronic disease, particularly in persons of Asian or Mediterranean descent.

• Unexplained haemolytic anaemia.

• The patient's partner has been diagnosed with a haemoglobinopathy or thalassaemia and the couple are in the child-bearing age group.

see also Haemoglobins, normal and abnormal

Haemoglobins, normal and abnormal

The haemoglobin (Hb) molecule consists of two pairs of polypeptide chains with a haem attached to each. The porphyrias are due to disorders of haem synthesis. The haemoglobinopathies are due to disorders in the globin chain pairs which are labelled á â ä ã etc. In the haemoglobinopathies, the amino acid sequence in a globin chain can be abnormal, or there can be a quantitative abnormality in globin chain production.


HbA á2â2 The normal adult Hb comprising 97% of the total. Also called HbA1. HbA1c, of interest to diabetologists, is the non-enzymatically glycated fraction of HbA1.

HbF á2ã2 foetal Hb comprises 70-90% of the total at birth falling to 1% by age

2. It is increased in ß thalassaemia and hereditary persistance of HbF (HPFH).

HbA2 á2ä2 the minor component of adult Hb comprising 1.5-3.2% of the total. It

is increased in ß cell thalassaemia.

HbH ß2ß2 is increased in the α thalassaemias in which there is deletion of deletion of 1-4 of the ã chains. In the 3-chain deletion HbH disease, HbH comprises 5-30% of total Hb.

HbS the cause of sickle cell anaemia (HbSS) found in South Africans and

occasionally in those of Mediterranean or Middle Eastern origin. The heterozygous state HbAS, is asymptomatic.

see also Haemoglobinopathy screen

Thalassaemias Sickle cell test

Haemoglobinuria

Haemoglobinuria indicates intravascular haemolysis with passage of Hb from plasma through glomeruli into urine. It does not include Hb released from intact red cells in urine.

see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections).

Causes of true haemoglobinuria include:

• strenuous exercise ("march" haemoglobinuria)

• some drugs - sulphonamides, quinine, phenylhydrazine


• infections - malaria, yellow fever, scarlet fever, septicaemias

• other - severe burns, incompatible transfusion, paroxysmal nocturnal haemoglobinuria (PNH) or paroxysmal cold haemoglobinuria (PCH)

In chronic haemoglobinuria such as PNH, haemosiderin may be detected in urine.

Haemolysis The features of haemolysis are:

• anaemia

• polychromasia � reticulocytosis

• haptoglobins - reduced or absent

• hyperbilirubinaemia

The blood film is used to distinguish between spherocytic and non-spherocytic haemolytic anaemia:

spherocytes present spherocytes absent hereditary spherocytosis hereditary elliptocytosis autoimmune haemolysis haemoglobinopathies (Coombs positive) enzymopathies (e.g. G-6-PD deficiency) drug-induced haemolysis PNH delayed transfusion reaction ABO incompatibility in the newborn

Haemolytic disease of the newborn see Bilirubin, total


Haemophilia

The haemophilias are due either to Factor VIII deficiency (classical haemophilia) or Factor IX deficiency (Christmas disease). Spontaneous mutations account for 30% of new cases in the absence of a family history. Severe haemophilia presents early in infancy but mild haemophilia can present later in life following surgery or trauma.

Diagnosis is from:

• clinical bleeding history

• family history

• abnormal APTT (correcting with 1+1 test)

• reduced level of FVIII or FIX

• DNA genotyping

see also Bleeding disorders

Coagulation screen

Haemosiderin

A granular storage form of iron which can be seen histologically. Physiologically it is the normal storage form of iron in bone marrow. Pathologically it is found in many parenchymal tissues in iron-overload. S. ferritin levels reflect tissue haemosiderin load.

In chronic haemoglobinuria, haemosiderin may be detected in a fresh random urine.


Hair for fungi see Dermatophytes

Hairy cell leukaemia

This is a rare form of B cell leukaemia (1-2%) with a 5:1 male predominance. It is characterised by pancytopenia, circulating 'hairy cells' and splenomegaly (80%).

Treatment is highly effective with ≥ 80% complete remission after one course of one week followed by a long period of complete remission.

Ham's test

see Paroxysmal nocturnal haemoglobinuria (PNH)

Hansen's bacillus see Leprosy

Haptoglobins

specimen: serum



Haptoglobin estimation is one of the screening tests for haemolysis. Hb released by the haemolytic process combines with haptoglobin to form a complex which is removed by the liver. It is also an acute phase reactant, migrating with the alpha-2 band on protein electrophoresis.

It is reduced by:

• haemolysis � haptoglobins are absent in moderate or severe haemolysis

• oestrogens, oral contraceptives, pregnancy

• acute or chronic hepatocellular liver disease

• specific genotype

• lower in first year of life � almost absent in first 6 weeks.

It is elevated by:

• biliary obstruction

• many acute or chronic inflammatory disorders � following recovery from an infective episode the level falls to normal within 10-14 days.

• specific genotype

Hb ( haemoglobin) see Blood count


HbA1c (glycated Hb) specimen: whole blood (EDTA)

ref. ranges: %Non-diabetic range: 4 - 6Diabetic range: excellent control 6 - 7 good control 7 - 8 indifferent control 8 - 9 poor control 9 - 10 exceptionally poor control >10

HbA1c is a measure of the mean blood glucose level over the previous 2-3 months and particularly the previous 4 weeks. It provides the essential baseline measure of glycaemic control in a diabetic and should be measured at least annually in all diabetics and more often (say 3-monthly) when assessing the affect of changes in therapy or compliance.

Unlike fructosamine, HbA1c is unaffected by proteinuria or obesity. It may be low however when there is shortened red cell survival as in haemolysis or bleeding.

The central role of HbA1c in assessing glycaemic control arose out of the DCCT (Diabetes Control and Complications Trial) which followed 1441 insulin dependent diabetics between 1983 and 1993. Intensive control compared with standard control reduced the risk of development and progression of retinopathy, nephropathy and neuropathy by approximately 60%. Risk of complications rose with increasing HbA1c with a significant steepening of the curve above a value of 8%.

Correlation of HbA1c with mean blood glucose


approximateHbA 1 c mean glucose

% mmol/L5 56 67 88 109 1210 14

HBV see Hepatitis B (HBV)

hCG (human chorionic gonadotrophin)

specimen:

• quantitative hCG serum

• qualitative pregnancy test serum (preferably) or random urine

ref. range: non-pregnant female or male <5 IU/L.

Qualitative pregnancy tests turn positive at around 25 IU/L.

hCG differs from the pituitary gonadotropin LH, only in its beta chain, hence the prefix "beta" sometimes applied to hCG. LH is otherwise structurally and functionally identical to hCG.


hCG in normal pregnancy

The developing placenta begins producing hCG about 3 days after implantation.

The sequence of events is:

Gestation Mean hCG(weeks) (units)

1st day LMP (last monthly period) 0 0fertilisation 2 0implantation 3 0placenta produces measurable hCG 3½ 101st day of missed period 4 100gestational sac becoming visible on ultra-sound 5 1,500peak hCG level 9 120,000

A single measurement of hCG answers the question whether a pregnancy is present or not.

Adding a second hCG or a series and plotting them on the hCG graph gives valuable information on the health of the embryo.

In a normal pregnancy, the hCG doubles every 1½ days between weeks 3½ and 6 and the trajectory rises parallel to the graph's percentile lines with remarkably little deviation.

A plot which is rising parallel to the percentile lines but outside the 5th-95th range indicates a healthy pregnancy with incorrect dates.

A graph rising more slowly, or flattening, usually indicates the onset of spontaneous abortion or an ectopic pregnancy and is an indication for proceeding with vaginal ultrasound looking for an intra-uterine gestational sac.

hCG in ectopic pregnancy


hCG is nearly always detectable in ectopic pregnancy and its absence makes the diagnosis most unlikely.

Levels may be

• low for dates � below the 5th percentile

• rising more slowly than normal

• flat or declining

hCG quantitation must be combined with ultrasound which will detect an intra-uterine sac after 5 weeks in a normal pregnancy. Using an abdominal probe, the intrauterine sac is visible with an hCG above 2000 units; with a trans-vaginal probe, the sac can be visible at 1000 units. In ectopic pregnancy there is, of course, no intra-uterine sac.

hCG after spontaneous or induced abortion After foetal loss or death, the hCG falls over a period of 1-5 weeks depending on its initial height and the completeness of elimination of placental tissue. The starting hCG depends on gestational age and health of the conceptus.

hCG in hydatidiform mole and choriocarcinoma The abnormal trophoblastic tissue produces large amounts of hCG whose levels are usually either high normal or clearly above the 95th percentile, sometimes as high as 1,000,000 IU/L. Ultrasound will separate a hydatidiform mole from a multiple pregnancy which can also have an hCG level above the 95th percentile.

After evacuation of a mole, the hCG is measured weekly until it has been normal (<5) for at least a month; and then monthly for at least 6 more months.

Absolute hCG levels are more method-dependent in trophoblastic disease and tumours than in normal pregnancy where levels should be repeatable between laboratories with different methods. In tumours, there are varying amounts of free beta chains and beta fragments, and different methods measure these to a varying


extent. For this reason, when monitoring a tumour, specimens should be sent to the same laboratory.

hCG in other tumours Ovarian and testicular germ cell tumours commonly produce hCG and a variety of malignancies from other sites can occasionally secrete hCG. Levels are used for monitoring treatment � but see paragraph above.

HDL cholesterol see Cholesterol, HDL

Heaf test see Tuberculin test (Mantoux test)

Health reforms These are in progress all over the world, which is waiting expectantly.

Heavy metals

Heavy metal poisoning is usually industrial in origin.

see Lead, blood, Arsenic, Cadmium, Chromium


Heinz bodies specimen: whole blood (EDTA)

Heinz bodies are red cell inclusions seen in haemolytic anaemias due to drugs, in haemoglobinopathies, and sometimes in normal people after splenectomy.

Helicobacter pylori

H. pylori, first described in 1984, lives in the mucus layer on the surface of the gastric mucosa where it causes gastritis and in some people, peptic ulcer disease (PUD), either duodenal or gastric. Antimicrobial therapy is usually curative. H. pylori is also a significant factor in the aetiology of gastric malignancy.

The organism, confined almost solely to humans and primates, is commonly acquired in childhood and persists for life. In Western countries the incidence of infection, like PUD, is decreasing � <30% below age 30, whereas in developing countries, which have high rates of PUD and gastric cancer, the incidence is above 80%, perhaps due to poor nutrition and hygiene.

The H. pylori story is evolving rapidly, particularly where it involves gastric infections not associated with PUD.

Tests for H. pylori

1. Endoscopy with urease test on biopsy material This is an excellent investigation though expensive if used in all cases of

dyspepsia. 2. 13 Curea breath test


A test with better than 98% sensitivity and specificity for H. pylori infection. If it is negative, it is most unlikely the patient has PUD. If, positive and there are other diagnostic features of PUD, e.g. past history, and endoscopy or x-ray imaging are not available, it may be reasonable to embark on antimicrobial therapy without further investigation.

The urea breath test is the preferred test of eradication, 4-6 weeks after anti-microbial therapy.

To perform the test, the patient takes a measured dose of 13C urea (non-radioactive). If H. pylori is present in the stomach its associated urease splits the molecule releasing 13CO2. A breath sample collected after 30 minutes is subsequently analysed for presence of 13C. The result is reported as positive or negative.

Antibiotics, bismuth and proton pump inhibitors can give false negative results.

3. Antibodies A variety of tests are in use, all of them with significantly poorer

performance than the breath test. Laboratory-based tests typically have a sensitivity/specificity of 85-95% whereas the office-based tests fall as low as 65%.

The suggestion, sometimes made in the past, that a single positive office-based test is indication for eradication therapy, is not valid.

In their present state of development, antibody tests may provide supportive evidence but another investigation will nearly always be necesssary.

Antibody tests are of no use as a test of eradication after therapy.

Treatment


Once H. pylori infection has been established, treatment is recommended for:

� gastric or duodenal ulcer disease, whether active or in remission � family history of gastric carcinoma; studies are in progress to determine

whether eradication reduces risk � MALT lymphoma of the stomach

Non-ulcer dyspepsia

There is insufficient evidence to recommend general treatment though in individual cases it is sometimes tried.

Recommended regimens include:

Different regimens are being trialled all the time, particularly the newer short course regimens. They can vary greatly in cost.

Here are two typical regimens.

• 2-week course– colloidal bismuth 120mg 6hrly– metronidazole 400mg 8 hrly– tetracycline 500mg 6 hrly or amoxycillin 500 mg 6 hrly

• 1-week course– omeprazole (or other PPI) 20mg bd– amoxycillin 500mg 6hrly– clarithromycin 500mg 6hrly– metronidazole 400mg 8hrly


HELLP Syndrome

An obstetric emergency characterised by Haemolysis, Elevated Liver enzymes and Low Platelets. Managed by early delivery and supportive care in a specialist maternity unit.

Henoch-Schönlein Purpura

A non-thrombocytopenic purpura due to a hypersensitivity vasculitis. Platelet count and coagulation tests are normal.

Glomerulonephritis is common, with haematuria and proteinuria.

Heparin therapy

For established deep-vein thrombosis or pulmonary embolism, anticoagulation with heparin remains the mainstay of acute treatment, followed by warfarin therapy to reduce the risk of recurrence.

IV Heparin

The older mode of therapy uses an IV infusion of unfractionated or standard heparin monitored by APTT estimations.

A 1.5-2.5 fold increase in APTT relative to baseline corresponds to a heparin level of 0.2-0.4 units/ml plasma.


SC low molecular weight heparin (LMWH)

LMWH has largely superseded IV standard heparin therapy.

The dose of LMWH is calculated from body weight and is given subcutaneously once or twice daily on an outpatient basis. Clexane (enoxaparin) and Fragmin are the two most commonly used LMW heparins in New Zealand.

No laboratory monitoring is required.

Clinical treatment trials in venous thromboembolism indicate that LMWH is at least comparable to standard heparin and may be superior.

Heparin tubes see Tubes for blood collects


Hepatitis

Hepatitis is characterised by elevations of ALT and AST and a histological picture on biopsy which may be diagnostic. When ALT and AST are above 1000 U/L with ALP and GGT below 300 u/L, the cause will usually be viral infection. In chronic hepatitis, changes in ALT are used as an indication of disease activity.

Main causes of hepatitis include:-

� Viral infection

� hepatitis A virus (HAV) � hepatitis B virus (HBV) � hepatitis C virus (HCV) � EB virus (infectious mononucleosis) � other viruses � HIV � hepatitis D, E � CMV (cytomegalovirus) � coxsackie virus � sundry other viruses causing flu-like illnesses circulating in the community

• autoimmune hepatitis • alcoholic hepatitis • drug-associated hepatitis • other

It is difficult to know the relative frequency of the common viral causes but indicative figures from a 1992 Christchurch study are:

EB virus 50%

hepatitis A 15%


hepatitis B 15%

hepaittis C 15%

CMV 5%

Hepatitis antibodies & antigens

In general an IgM antibody develops first and then disappears within 3-12 months. It is the marker for current or recent infection.

IgG antibodies start soon after IgM, rise more slowly, but then persist indefinitely. They are a marker for both current and past infection but will not distinguish between the two. IgG antibodies are used to indicate immune status � has this person been infected in the past? Has this person's vaccination been effective?

"Total" antibodies measures both IgM and IgG in a single test. When IgM, IgG are not specified, e.g. anti-HAV, this means "total", i.e. both IgG and IgM.

Some antibodies indicate solid immunity e.g. anti HBs.

Others do not indicate immunity, only past or current infection, e.g. anti HCV, antiHBc.

Antigens show the presence of virus indicating current infection, carrier status or chronic hepatitis, e.g. HBs antigen, HBe antigen, HCV-RNA, HDV-RNA.

Hepatitis A (HAV)


specimen : serumtests : · anti-HAV IgM

· anti–HAV IgM and IgG (total antibody) There is no test for HAV antigen.

Interpretation:

The IgM antibody appears at about the time clinical symptoms develop and persists for 6-12 months. This anti-HAV IgM is the marker for current or recent infection.

The IgG appears not long after the IgM but persists for life and is thus the marker for HAV immune status.

Active Immunisation:

Havrix, the HAV vaccine, became available in 1992 and provides solid immunity.

It should be recommended to any traveller going to countries where hygiene might be suspect. Travellers with previous experience may find they are already immune, as shown by presence of anti-HAV IgG, even though they have no recollection of clinical disease.

Two IM injections 6-12 months apart provide immunity for many years. When there is urgency, a single double-strength injection just before departure has been shown to provide useful protection for up to two years. A second injection provides long-lived immunity even when given years after the initial injection.

Passive Immunisation

Contacts of a person with active HAV infection should be given passive protection with immune globulin 0.02 ml/kg IM provided it can be given within two weeks of exposure.


In travellers, life-long protection with Havrix has almost completely replaced passive protection using immune globulin.

Clinical course

Hepatitis A is spread by faecally contaminated water, or an infected food handler. It is found frequently in third world countries and is still common in New Zealand. The diagram shows the usual time course.

Infectivity due to faecal shedding of virus, is at its height one week before clinical symptoms develop and persists for about 4 weeks.

Hepatitis A can relapse up to 6 (or even 12) months after the first bout but does not persist thereafter, so is never a cause of chronic hepatitis, cirrhosis, or hepatocellular carcinoma.


Hepatitis B (HBV) specimen: serum

tests: HBs Ag (HBV surface antigen)HBe Ag (HBV e antigen)anti-HBs (antibody to HBV surface antigen)anti-HBe (antibody to HB e antigen)anti-HBc IgM (IgM antibody to HBV core antigen)anti-HBc (IgM and IgG antibody to HBV core)HBV-DNA (HBV-DNA detected by PCR)

Indications and interpretation

1. HBs antigen If positive indicates � acute HBV infection (enzymes elevated) or � chronic HBV infection (enzymes fluctuate) or � HBV carrier (enzymes not elevated) 2. HBe antigen This should be checked whenever HBs antigen is positive. If HBe antigen

(Ag) is present, it indicates greater infectivity of the HBV infection towards sexual partner or foetus and greater likelihood of developing chronic hepatitis. HBe Ag is found only in association with Hbs Ag, never on its own.


3. Anti-HBs Indicates immunity to HBV whether naturally acquired or following

immunisation. Anti-HBs can be measured quantitatively � levels above 10 IU/L indicate immunity.

4. Anti-HBc IgM Is measured when current HBV infection is strongly suspected but HBs Ag

and anti-HBs are both negative. Anti-HBc IgM rises early in HBV infection and persists for about 6 months. It fills the one month "window" between disappearance of HBsAg and the appearance of anti-HBs. Positive anti-HBc does not confer immunity.

5. Anti-HBc total Indicates past infection but unlike anti-HBs it does not indicate immunity and

can coexist with HBs Ag in carriers or chronic hepatitis. Anti-HBc remains negative after HBV vaccination because the vaccine

contains s but not c antigen. 6. Anti-HBe In chronic HBV infection, anti-HBe indicates low infectivity. 7. HBV - DNA If positive indicates HBV viraemia which is an indication for considering

interferon treatment in chronic infections.


HBs antigen in pregnancy

HBs Ag is routinely checked antenatally. If positive, this indicates carrier state or, less often,current infection.

The infant of an HBs Ag positive mother will need immune globulin (anti-HBV) at birth and the first dose of a course of HBV immunisation.

Immunisation against HBV

The standard course is three IM injections at 0, 1 and 6 months. It is indicated in the following situations:

• neonates born to carrier mothers

• sexual partners of a carrier

• health workers at significant risk from needle-stick injuries or who come in contact with blood, e.g. nurses, doctors, laboratory workers (see Accidental inoculation of infected blood).

• IV drug users

An initial anti-HBs test will determine whether immunisation is necessary. Presence of anti-HBs indicates immunity. Presence of HBs antigen means that immunisation will be ineffective. Follow-up should be provided to those found to be HBV carriers.

Opinion is divided whether the antibody response to immunisation should be measured. The UK recommendation is to give a further booster if anti-HBs is <10 whereas American recommendations assume that protection exists even when the level falls to <10 as long as the person has seroconverted to the vaccine.


Some people fail to seroconvert at all to the standard course. If they are considered at particular risk, alternative protocols can be discussed with a clinical microbiologist.

Epidemiology of HBV

4% of the world population carry HBV but most of those infected are in Asia. In New Zealand about 0.4% of European blood donors are HBV positive compared with about 5% of Maori and Pacific Islanders.

Infection is by mother-to-neonate, sexual transmission, IV drug use, infection, or administration of infected blood products. Often the mode of infection cannot be identified and it is assumed there has been some less obvious transmission such as inoculation of blood or saliva into lacerations or abrasions in childhood or during contact sport or whatever.

About 1-2 % of HBV infected adults fail to eradicate infection and become carriers or develop chronic hepatitis with its possible sequelae of cirrhosis and hepato-cellular carcinoma. The risk of developing chronic infection is much higher in children and particularly in neonates.

Follow up on HBs Ag +ve patients

ALT is the test used to decide whether the patient has active disease that should be considered for anti-viral therapy.

If the ALT >60 units, it should be repeated in 4 months. If the elevation >60 persists, the patient should be referred for specialist follow-up.

HBe Ag should also be checked and repeated annually if found to be positive.


Hepatitis C

specimen : serum

tests : · anti HCV (total antibody to HCV)· HCV-RNA

Indications and interpretation

1. Anti-HCV Used when hepatitis C is a possibility, e.g. IV drug users, raised liver

enzymes of unknown cause.

Anti-HCV starts to rise 1-6 months after the initial infection and persists for life. Presence of anti-HCV indicates either past infection or continuing chronic infection.

2. HCV-RNA This is a follow-on test when anti-HCV is positive. It is also used when

clinical suspicion of HCV infection is high but anti HCV is negative because infection is recent or the patient immuno-suppressed.

It indicates current active HCV infection and is an indication for considering interferon and ribavirin therapy.

Clinical course & epidemiology

HCV was identified in 1989 having previously been included in the non-A non-B hepatitis category. 0.25% of people presenting as blood donors in New Zealand are positive for HCV. A random population sample in the United States shows 1.8% positiviity.


Transmission in blood products has been largely eliminated, leaving contaminated needles in drug users as the main source of new infections. In New Zealand HCV antibodies have been found in 80% of injecting drug users, 65% of haemophiliacs, 15% of homosexual men, 11% of patients with cirrhosis. It is the cause of 5-15% of acute non-A, non-B hepatitis.

Mother-to-foetus transmission occurs but is infrequent, <5%. Sexual transmission is believed to be uncommon.

More than 50% of HCV infections become chronic with potential to develop cirrhosis and hepatocellular carcinoma.

Treatment with a combination of interferon and ribavirin clears the virus in about 50% of patients.

There is no vaccine yet.

Follow up on HCV +ve patients

A positive HCV Ab test should be followed by HCV RNA test and ALT.

If HCV RNA is positive, the patient should be referred for consideration of anti-viral therapy.

An ALT >60 units indicates active disease but a level <60 does not exclude activity.

The patient who is HCV Ab +ve but HCV RNA �ve is presumed to be free of active hepatitis provided the ALT is <60. The ALT should be monitored annually and the HCV RNA for at least 2 years to confirm it is staying -ve.


Hepatitis D (HDV - Delta)

specimen : serumtests : · anti Delta IgG

· HDV RNA

HDV infections are found only as a co-infection or superinfection in HBV positive patients. HDV is associated with more severe acute disease and a greater risk of developing chronic hepatitis and its complications.

HDV infections once established, will persist for as long as HBV carriage continues, but if HBV is eliminated HDV will go with it.

Anti-delta antibodies indicate either current active infection or past infection with immunity.

Positive HDV RNA indicates current active infection.

Hepatitis E (HEV)

specimen: serum

test: anti HEV IgG

Hepatitis E resembles hepatitis A in its faecal-oral mode of transmission. It is endemic in India, SE Asia, China, Mexico and parts of Africa.

Presence of HEV antibodies does not distinguish current from past infection.


Identifying the virus in a small specimen of faeces may identify current infection.

Hepatitis due to EB Virus

see Infectious mononucleosis

Hepatitis, autoimmune specimen: serumtests: • smooth muscle antibodies

• antimitochondrial antibodies• liver/kidney microsomal antibodies• ANA• anti ds DNA• immunoglobulins

Autoimmune hepatitis, formerly known as chronic active hepatitis and before that lupoid hepatitis, affects predominantly young women. The hepatitis can be of all grades of severity ranging from minor enzyme elevations in a well person to a clinical laboratory picture like that of severe viral hepatitis. Diagnosis is by excluding viral causes; by finding specific autoantibodies; by markedly elevated IgG; and by liver biopsy.

Smooth muscle antibodies (SMA) in high concentration (>80) define autoimmune hepatitis. Antimitochondrial antibodies (AMA) and total IgM may be elevated but these are typically the markers of the other autoimmune liver disease, primary biliary cirrhosis. Liver/kidney microsomal antibodies (LKM) are uncommon but help in disease classification. Titres tend to be lower in viral hepatitis than in autoimmune hepatitis.


Hereditary elliptocytosis see Elliptocytosis

Hereditary spherocytosis

A relatively common haemolytic disorder found in all races and typically inherited as an autosomal dominant. In the 25% of individuals who have unaffected parents, the disease is assumed to be due to autosomal recessive inheritance or a spontaneous mutation.

More severe forms present in the first 10 years of life but milder forms may be discovered incidentally either on a blood count or because of a minimally elevated bilirubin resembling Gilbert's Syndrome.

Laboratory tests typically show the features of a haemolytic disorder � increased reticulocytes, reduced haptoglobins, hyperbilirubinaemia, anaemia.

The more specific findings are:

• spherocytes on the blood film

• increased osmotic fragility (qv) of red cells

Herpes simplex virus (HSV)

specimen: air-dried smear of vesicular cells on a glass slide


Virus is found in tissue cells at the base of the vesicle. A sharp needle can be used to rupture a newly-formed vesicle and scrape tissue cells from the base. The scrapings are smeared on a glass slide as two spots, 1cm in diameter, one each for herpes 1 and 2. If the lesions are already crusted, the crust must be removed before taking smears using needle or spatula.

The spots are air-dried and the slide labelled with the patient's name, date of collection and the word 'herpes'. In the laboratory, an immunofluorescent stain is used to detect virus.

There are two types of herpes simplex, HSV1 and HSV2.

HSV 1 commonly gives rise to recurrent oral infections ("cold sores") and HSV 2 to recurrent genital infections but either can be found at either site.

Other tests � the virus can be cultured (use the special transport swab) and antibody tests can differentiate HSV-1 from HSV-2.

Herpes zoster see Varicella-zoster virus (VZV) virus

Heterophile antibodies see Infectious mononucleosis


HFE gene for hereditary haemochromatosis specimen: ACD tube for genetic studies

interpretation � see Haemochromatosis

HGH (human growth hormone) see Growth hormone (HGH, somatotropin)

HIAA (5-hydroxy indole acetic acid)

specimen: 24-hr urine collected into acid

ref. range: <50 µmol/day

Avoid the following drugs and foods for 3 days before collecting the urine.

phenothiazines bananas tomatoesmethyldopa plums egg plantnaprosen pineapple avocadocough mixture fruit juices walnutsacetaminophen kiwifruit pecans

In carcinoid syndrome the HIAA is usually >80. Results in the 50-80 range should be repeated.

Carcinoid syndrome, due to release of serotonin from a carcinoid tumour, is characterised by cutaneous flushing, diarrhoea, valvular heart disease, and less often by wheezing, paroxysmal hypotension and telangiectasia. HIAA is the breakdown product of serotonin and is usually measured in response to a history of flushing though this is more commonly due to menopause, alcohol (particularly in


combination with a sulphonylurea or disulfiram). Phaeochromocytoma is infrequently a cause of flushing.

Hirsutism/virilism

The spectrum of hirsutism ranges from the upper percentiles of normal hair growth through to the male-pattern hair growth, amenorrhoea and genital virilisation of androgenic tumours.

The common cause of hirsutism is polycystic ovary syndrome (qv).

Rarer causes of hirsutism/virilism and tests for them are:

� adrenal tumours testosterone, DHEAS, androstenedione � ovarian tumours testosterone, androstenedione � adult onset adrenogenital syndrome 17-OH progesterone � Cushing's syndrome 24-hr urine free cortisol � hypothyroidism TSH, T4 � drugs - danazol, phenytoin, cyclosporin, minoxidil

Histology – specimen preservation

Specimens should be placed in 10% formal saline fixative in a container of sufficient size to allow a ratio of volume of fixative to specimen of at least 5 to 1.

Containers must be carefully labelled with name of patient, date of birth, nature of specimen, date, name of doctor.


Biopsy specimens of small size require special care and should be placed in 10% formal saline as quickly as possible to prevent drying artefact. Small biopsies should not be placed on gauze or paper as this causes drying.

Special fixatives for biopsy specimens, e.g. Bouins fixative for testicular biopsies, are also available.

Oestrogen and progesterone receptors on breast cancers are now routinely performed on formalin fixed tissue rather than using a specimen forwarded on ice.

Skin for direct immunofluorescence microscopy (DIF), usually for the investigations of blistering or bullous disorders, needs to be submitted to the laboratory fresh on damp saline-soaked gauze inside a specimen pot packed in ice. The specimen needs to be snap frozen in the laboratory within 2 hours of the specimen being taken. The pathologist should be contacted 24 hours before taking the biopsy to ensure rapid handling of the specimen.

see also Skin biopsy

Malignant melanoma

Prostate cancer � histological grading

HIV (human immunodeficiency virus)

specimen: serum tests: an initial screen test with >99% sensitivity followed by a

confirmatory test for those who screen positive. The screen test detects both HIV-1 (the commonest) and HIV-2. A DNA-based test is available for babies born to seropositive mothers.

Patient ID


If anonymity is required, the patient is identified by a code using the first 2 letters of the patient's surname, first initial, sex and date of birth, e.g. John Harris, male, d.o.b. 18/9/47, becomes HAJM180947. If you are unsure about the need for anonymity or forget to ask, assuming it is required is a good philosophy.

Test interpretation

The screen test has a cut-off level of 1 unit. Below this the test is reported as negative. Above 1 unit, the serum is referred for the more specific Western Blot test. Results in the 1-1.5 unit range can be false positive screen results due to cross-reactivity with other viral antigens and the level may fall below 1, i.e. become negative, on subsequent testing. Patients with established HIV infection typically have results in the 5-20 range. A screen result of 1-2 with negative Western Blot should be repeated in a month.

A negative antibody test does not exclude HIV infection during the first few months after transmission of the virus but for practical purposes, all those infected will test HIV positive within 6 months.

The median time from infection to the development of AIDS is about 10 years.

Prevalence of HIV in New Zealand

By mid 1999, 1,355 patients had been reported with HIV infection since the beginning of the epidemic and 678 with AIDS. Currently there are about 700 HIV infected people living in New Zealand of whom 107 have AIDS. Homosexual males remain the biggest identifiable risk group (63% now) but in the last 18 months infected heterosexual immigrants, particularly from Africa, are the most rapidly increasing group. After falling for several years, the number of newly reported HIV infected people rose in 1998, significantly contributed to by this immigrant group.

Presentation

GPs are the group who most frequently test for and diagnose HIV infection in New Zealand, far more than hospital, sexual health clinics or special clinics combined.


Sometimes an HIV screen is requested "as an outside possibility", without mentioning the test to the patient. The current advice and recommendation is that an HIV test should always be discussed prior to testing with pretest counselling as seems appropriate.

Early symptoms of HIV include exacerbation of previous skin disease, e.g. eczema, somewhat recalcitrant tinea, surprising shingles, oral candidiasis, recalcitrant vaginal candidiasis : in other words, common or ordinary events occurring oddly or excessively.

Lymphoma predisposes to HIV infection and HIV is an uncommon cause of acute immune thrombocytopenia.

Pneumocystis carinii pneumonia (found only when patients have CD4 counts <200/cmm and essentially preventable) is most often a creeping, slow illness with dry cough, fever and shortness of breath which may not be easy to diagnose or confirm.

Monitoring Viral load The concentration of virus in the plasma can now be measured. As a generalisation the higher the concentration (max. 1,000,000 or 610 copies/ml) the more rapid will be progression in time to clinical illness and AIDS. The lower the concentration (at present the lowest level of detection is 500 or 10 27 copies/ml), the slower the disease progression.

The aims of treatment are to suppress this level as low as possible.

CD4 counts The concentration of this lymphocyte subset correlates with the stage the patient's immune system has reached in its battle with HIV. The lower it is (normal >500 cells/cmm) the more likely will that individual have illness, with the risk rising progressively as it falls below 200 and then below 100 cells/cmm.

Treatment


Treatment requires use of at least two agents and most commonly three, to slow virus replication, minimise development of resistance, preserve and augment immune function and thus minimise clinical illness and prolong life.

The moment to begin treatment is ill defined : with CD4 counts <350 cells/cmm and a high viral load, few would not wish to treat or be treated. At higher CD4 counts and lower viral loads, everyone has a different opinion and individual patient views are often the ultimate determinant for the decision.

see also CD4 T-lymphocytes Microglobulin Needlestick injuries Pancytopenia Liver enzymes

HLA-B27 antigen (human leucocyte antigen B27) specimen: blood (CPD tissue typing tube)

HLA B27 has a frequency of 7-10% in the general population but a much higher frequency in the sero-negative spondyloarthropathies which are characterised by:

� sacroileitis and spondylitis, causing low back pain and loss of lumbar mobility

� tendonitis, including heel pain and other pain at muscle and tendinous insertion

� oligoarthritis � urethritis � iritis and conjunctivitis


As indicated by the term seronegative, all of these disorders are negative for rheumatoid factor.

The principal members of the group with the % positivity for HLA B27 are:

• ankylosing spondylitis (95%-98%)

• Reiter's disease (90%)

• arthropathies associated with ulcerative colitis and Crohn's disease (70%)

• post-enteric and post-venereal reactive arthritis (70%)

• psoriatic arthritis (30%)

HMMA (hydroxy methyl mandelic acid) specimen: 24-hr urine collected into acid

ref. range: <40 µmol/day

Also known as VMA, vanilly mandelic acid. This is a follow-up test for suspected phaeochromocytoma, usually used only when catecholamine fractions, particularly noradrenaline, have shown equivocal elevations.

see also Catecholamines

Homocysteine, plasma

specimen: fasting plasma (EDTA) stored on ice prior to centrifugation ref. range: 5-15 µmol/L


Previously, clinical interest in homocysteine in blood was confined to the rare inborn error of metabolism homocystinuria (qv) in which plasma homocysteine is markedly elevated to above 100 µmol/L.

More recently an association has been described between mild to moderate hyperhomocysteinaemia (15-100 µmol/L) and cardiovascular disease and many now regard it as an independent risk factor for coronary, cerebral and peripheral arterial disease.

Increasing intake of folic acid and to a lesser extent vitamin B6 and perhaps B12 may lower homocysteine levels. A daily supplement of 400 µg folic acid will in most patients increase serum folate above 15 nmol/L and drop plasma homocysteine to a low plateau. As yet there is no proof of a favourable affect on cardiovascular outcomes.

Homocysteine elevation above 20 µmol/L is also a risk factor for venous thrombosis (2-3 x increase).

Homocystinuria/homocysteinuria

A rare (1:50,000) recessive inborn error of metabolism characterised by markedly elevated levels of homocysteine (qv) in blood and homocystine in urine.

Clinically it can present as tall marfanoid stature, arachnodactyly, myopia, lens subluxation, premature atherosclerosis, thromboembolic events.

The screen tests are plasma homocysteine and a urine screen test for elevated homocystine/cystine.


Homovanillic acid see HVA (homovanillic acid)

Hookworm

Hookworm refers to intestinal infestation with Ancylostoma duodenale (found in the Mediterranean basin, the Middle East, India and China) or Necator americanus (found in the Americas, sub-Saharan Africa and SE Asia). Heavy infestations are an important cause of iron-deficiency anaemia.

Diagnosis is by identifying eggs in faeces.

Treatment is with mebendazole 100mg, 12-hourly for 3 days.

Howell-Jolly bodies

These are residual nuclear remnants seen in red cells after splenectomy and sometimes in megaloblastic anaemia or haemolysis.

see also Hyposplenism

HPV (human papilloma virus)

HPV causes sexually transmitted genital warts and is associated with dysplastic changes and sometimes carcinoma in the cervix.


Human chorionic gonadotropin see hCG (human chorionic gonadotrophin)

Human genome

Some statistics:-

3.3 x 109 base pairs 3 x 1012 cells in the body 2 metres of DNA/cell 6 x 1012 metres of DNA/individual which is 8,000 times the distance between earth

and moon.

There are 50,000 - 1,000,000 different genes of which 3,000 have been mapped.

The human genome project aims to develop a powerful genetic and then physical map and subsequently to determine the complete nucleotide sequence.

HVA (homovanillic acid) specimen: 24-hr urine with acid preservative

ref . range: 3-42 µmol/day

HVA is the urinary metabolite of dopamine and is measured when investigating or monitoring neuroblastomas or malignant phaeochromocytomas.

see also Catecholamines


Hydatidiform mole see hCG (human chorionic gonadotrophin)

Hydatids specimen: serum

ref. range: negative

Positives are now rare in New Zealand.

25-hydroxy calciferol see Vitamin D

17-hydroxy corticosteroids Test no longer done. It has been replaced by the 24-hr urine free cortisol in the diagnosis of Cushing's syndrome.

5-hydroxy indole acetic acid see HIAA (5-hydroxy indole acetic acid)


5-hydroxy methoxy mandelic acid see HMMA (hydroxy methyl mandelic acid)

17-hydroxy progesterone (17-OHP) specimen: serum

ref. range:

nmol/Lmale female

before puberty 0.4-1.0 0.6-2.0adult 0.6-5.5 0.6-2.5 (follicular)

1.5-15 (luteal)

17-OHP has replaced urinary pregnanetriol as the best screening test for the most common form of congenital adrenal hyperplasia (CAH) and is checked in the National Testing Centre neonatal screening programme.

17-OHP is a precursor of cortisol, androgens and oestrogens. In CAH, a block in the cortisol pathway leads to overproduction of 17-OHP and androgens.

see also Congenital adrenal hyperplasia (CAH)

Hydroxybutyrate

see Beta-hydroxybutyrate


Hydroxyproline specimen: 24-hr urine with acid preservative.

ref. range: <0.38 mmol/day

This marker for bone turnover has been superseded by N-telopeptide.

see Bone turnover markers N-telopeptide

Hyper Greek for over, beyond.

Most hyper- entries are listed under the term they qualify, e.g. hypermagnesaemia is described under magnesium.

Hyperbilirubinaemia


Hypercoagulability

Hypercoagulability (thrombophilia) is the term used to describe an increased risk of thrombosis. The risk factors causing hypercoagulability can be primary (inherited) or secondary (acquired) and when considering the aetiology of a thrombolic event, both types need to be considered. Risk is compounded when two or more factors are present.


A. Acquired risk factors• immobility• surgery• trauma• pregnancy• oral contraceptives• malignancies• antiphospholipid antibody syndrome• SLE• myeloproliferative disorders• PNH

B. Inherited risk factors

• activated Protein C resistance due to Factor V Leiden mutation

• antithrombin III deficiency• Protein C deficiency• Protein S deficiency• other

One of the first four of these inherited abnormalities is found in about 50% of cases of thrombosis. The Factor V Leiden abnormality is ten times more common than each of the other three.

The "other" category includes rare disorders such as homocysteinuria and the prothrombin 20210 G-A variant. There are also other as yet unidentified abnormalities which are presumed to exist.

Thrombotic Risk (Leiden Thrombophilia Study)Approximate DVT incidence

category relative risk (% per year)

normal 1 0.01% (1:10,000)OCs 2-4 0.02 - 0.04%FV mutation (heterozygous) 5-10 0.05 - 0.1%FV mutation + OC 30-50 0.3 - 0.5%FV mutation (homozygous) 100 1.0%ATIII, PrC, PrS 100 1.0%


Which patients should be tested for a genetic hypercoagulability?

• thrombosis in a patient <45 years

• recurrent thrombosis

• family history of thrombosis Who should not be tested?

Screening is not recommended:

� as a routine before starting oral contraceptives : the absolute risk of thrombosis is low, cost of screening is high, false positives occur, and an unwanted pregnancy may be blamed on withholding OC.

� before surgery when there are no other risk factors. � before pregnancy when there are no other risk factors. � in a patient over 45 with a first thrombosis which has been provoked by an

identified correctible risk factor.

Hyperparathyroidism see Calcium (total)

Hypersplenism


Splenomegaly, whatever the cause, leads to pooling of blood cells in the enlarged spleen and sometimes to increased cell destruction. The net effect can be anaemia, neutropenia or thrombocytopenia, either singly or in combination.

Hyperthyroidism see Thyroid disease � diagnosis and monitoring

Hypertension – endocrine causes

These include: Conn's syndrome Cushing's syndrome phaeochromocytoma renal artery stenosis acromegaly hyperthyroidism

Hypo Greek for under, below

Hypo-words are mainly entered under the terms they qualify, e.g. hypocalcaemia is under calcium.

Hypochromia see Microcytosis


Iron deficiency Percentage hypochromia

Hypogammaglobulinaemia

Hypogammaglobulinaemia can be found in:

myeloma

chronic lymphocytic leukaemia

lymphoma

non-selective protein loss

transiently with a recent viral infection

congenital deficiency

see Immunoglobulins, IgA, IgG, IgM

Hypoglycaemia

The glucose threshold at which symptoms of hypoglycaemia develop varies widely between individuals but in general a glucose level <3.0-3.5 mmol/L can be described as hypoglycaemic except in neonates where the lower limit of "normal" is about 2.5 mmol/L.

Hypoglycaemia in diabetics treated with insulin or sulphonylureas

Symptoms are common, diverse and often misinterpreted or overlooked. The transient nature of the hypoglycaemia means that laboratory collects usually miss the


trough but any value below 4.0 is suspicious. Symptoms and signs include irritability, tremulousness, faintness, sweating, pallor, hunger, weight gain, headache (headache on waking may be due to nocturnal hypoglycaemia), personality change, deterioration in level of consciousness, coma.

Reactive (functional) hypoglycaemia

This common but elusive syndrome with its symptoms of irritability, tremulousness and hunger ("faint with hunger") is not easily diagnosed by the laboratory. It is seen in children, young adults, and to a lesser extent older people. The symptoms are felt some 2-5 hours after food, not while fasting.

The extended GTT (4½-5 hrs) has been the traditional test but is a burden to the patient and has too many false positives and false negatives.

A marginally more useful test is the measured blood glucose during an attack but the logistics of this are often not easy.

The best test is a trial of diet which, if successful, combines diagnosis with therapy. Sweet refined carbohydrates are changed to unrefined carbohydrates with one or two snacks added between meals.

Fasting hypoglycaemias

These are much less common than the non-fasting varieties and much more likely to have an identifiable organic basis.

The first test is to measure a fasting glucose. If low it should be followed by a fasting insulin and repeat glucose:

• raised or inappropriately normal fasting insulin � insulinoma


� exogenous insulin or sulphonylureas

• low fasting insulin � advanced liver disease

� malignancy

� isulin autoantibodies

� alcohol

� pituitary/adrenal insufficiency

Neonatal hypoglycaemia

The at-risk infants are

• low birth-weight

• infants of diabetic mothers

In both, blood glucose levels should be monitored, beginning an hour after birth, and treatment given if levels are below 2.0-2.5 mmol/L. Glucose levels can rise and fall quickly during the neonatal period. Clinical signs are an inadequate indication of hypoglycaemia.

Hypopituitarism

Usually due to a tumour of the pituitary or hypothalamus but pituitary infarction or haemorrhage can occur in a normal pituitary, classically as Sheehan's syndrome after obstetric haemorrhage but also in other situations including bleeding disorders, cardiac by-pass surgery and some imaging procedures.

Clinically hypopituitarism may present as amenorrhoea, hypogonadism, hypothyroidism, adrenal insufficiency, hyponatraemia. Useful tests include:


Adrenal Synacthen test. A peak cortisol >700 nmol/L makes chronic hypopituitarism very unlikely though it may not exclude partial or very recent onset of hypopituitarism.

Thyroid T4 low but TSH usually normal. The TSH measured in this situation can co-exist with clinical hypothyroidism so is assumed to be biologically inert.

Gonads FSH and LH may be low, particularly in post-menopausal women who otherwise have high levels. Testosterone may be low in men.

Hyposplenism

After splenectomy, red cells show Howell-Jolly bodies, targeting and spherocytosis and there is thrombocytosis and leukocytosis which may or may not persist.

A hyposplenic blood picture can also be seen in other conditions associated with splenic atrophy :

• coeliac disease

• inflammatory bowel disease

• autoimmune disease, particularly with haemolysis

• sickle cell disease

After splenectomy a patient may have increased susceptibility to infection which can be overwhelming in children. Pneumococci are the usual cause but other organisms such as Haemophilus or meningococcus may be responsible. Pneumococcal and meningococcal vaccines can be given every 5-7 years or penicillin prophylaxis in susceptible patients.


Hypothyroidism see Thyroid disease � diagnosis and monitoring

I

IA autoantibodies (insulin antibodies) see


Diabetes autoantibodies

IA2 autoantibodies (insulin antigen 2) see Diabetes autoantibodies

IBC see Iron-binding capacity (IBC) and saturation

ICA autoantibodies (islet cell) see Diabetes autoantibodies

Idiopathic immune thrombocytopenic purpura see ITP (idiopathic immune thrombocytopenic purpura)

IEP


see Immunoelectrophoresis (IEP)

IF (immunofixation) see Immunoelectrophoresis (IEP)

IgA, IgG, IgM see Immunoglobulins, IgA, IgG, IgM

IgA deficiency

A selective reduction in IgA is a common congenital immune deficiency syndrome occurring in 1:700 people. It is usually detected by blood donor screening. Most individuals are asymptomatic. IgA deficiency is associated with autoimmune disorders including coeliac disease, SLE, autoimmune haemolytic anaemia, rheumatoid arthritis and thyroiditis.

Anaphylaxis may occur as a result of IgG antibodies to IgA when the individual is exposed to blood transfusion or gammaglobulin therapy.

see also Immunoglobulins, IgA, IgG, IgM

IgE total specimen: serum


ref. range: 0 - 100 IU/L

IgE antibodies mediate Type I allergic reactions � allergic rhinitis, asthma, atopic dermatitis, anaphylaxis.

Total IgE is elevated in patients with multiple allergies and parasitic infestations. Very high levels, above 1000 IU/L, are found with atopic dermatitis, fungal sinusitis and allergic pulmonary aspergillosis.

see also RAST (Radioallergosorbent test) for specific IgE antibody tests

IGF-1 (insulin-like growth factor-1, somatomedin C)

specimen: serum or plasma (EDTA)

ref. range:

age males femalesyears ng/mL ng/mL0 - 5 17 - 248 17 - 2486 - 8 88 - 474 88 - 474

9 - 11 110 - 565 117 - 77112 - 15 202 - 957 261 - 109616 - 19 182 - 780 182 - 78020 - 39 122 - 400 122 - 40040 - 54 75 - 306 75 - 306

>54 48 - 225 48 - 225

Levels peak at puberty during maximum growth

The action of human growth hormone (HGH) from the pituitary is mediated through IGF-1 which is formed in the liver. As well as its effects on growth, it has insulin-


like actions. IGF-1 synthesis is suppressed by malnutrition as well as HGH deficiency.

IGF-1 and HGH are measured in suspected acromegaly and in pituitary dwarfism.

Immune paresis This term refers to reduction in normal immunoglobulins

see Immunoglobulins, IgA, IgG, IgM

Immunoelectrophoresis (IEP) see Immunofixation (IF), serum

Immunofixation (IF), serum

specimen: serum

Immunofixation is used:

• to confirm the presence of a paraprotein when an abnormal band has been found on serum EPP

• to determine whether it is IgG, IgA or IgM, light chain only or, rarely, IgD or IgE

• to establish whether the light chain component is kappa or lambda

see also electrophoresis of urine


Immunoglobulins, IgA, IgG, IgM, Monoclonal bands

Immunofixation, urine specimen: urine, random

A test for free light chains (Bence Jones Protein), whether they are present and whether kappa or lambda.

see also Electrophoresis of urine Immunoglobulins, IgA, IgG, IgM, Monoclonal bands

Immunoglobulin G subclasses

The four IgG subclasses are numbered 1 to 4. In some patients, recurrent respiratory tract infections are associated with Ig subclass deficiency even though the total IgG is within the usual range.

Immunoglobulins, IgA, IgG, IgM specimen: serum

ref. ranges:


Age IgG IgM IgA

0 - 14 days 6.0 - 16.0 0.1 - 0.6 0.0 - 0.12 - 6 weeks 2.0 - 6.0 0.2 - 0.8 0.0 - 0.57 weeks - 6 months 2.0 - 7.0 0.2 - 1.0 0.0 - 0.87 - 24 months 3.0 - 10.5 0.3 - 1.5 0.1 - 1.22 - 5 years 4.5 - 11.5 0.5 - 1.9 0.3 - 1.66 - 10 years 6.0 - 13.0 0.5 - 2.1 0.4 - 2.211 - 16 years 6.0 - 15.0 0.5 - 2.2 0.7 - 2.3Adult 7.0 - 16.0 0.4 - 2.5 0.8 - 4.070+ yr 6.0 - 15.0 0.4 - 2.4 0.8 - 4.0

Quantitation of immunoglobulins, particularly paraproteins, is method-dependent so when monitoring a patient with myeloma or an apparently benign paraprotein, the immunoglobulins will ideally be measured by the same laboratory using the same method. In practice, laboratories change methods at times so when a result shows an unexpected rise or fall, the laboratory should be consulted.

Immunoglobulins are antibodies and constitute the gamma fraction of serum globulins. Abnormalities of immunoglobulins include:

� monoclonal increases, benign or malignant � polyclonal increases as seen in chronic inflammatory disorders � polyclonal decreases : immune paresis

Serum protein electrophoresis (EPP) is an essential test when interpreting a raised total globulin or immunoglobulin to determine whether a paraprotein is responsible for the increase.

A. Monoclonal bands, paraproteins, M-bands A paraprotein, which appears as a sharply defined abnormal band on serum EPP, consists of a single population of identical immunoglobulin molecules formed by a clone of neoplastic plasma cells. They can be benign (MGUS) or malignant (myeloma, macroglobulinaemia or lymphoma).


Occasionally an M-band is due to an extra-medullary plasmacytoma.

Benign paraproteins (MGUS – monoclonal gammopathy of uncertain significance)

These paraproteins, composed of IgG, IgA, or IgM, appear with increasing frequency in the elderly � 8% of patients over age 70. They can be transient, particularly in younger individuals. Characteristics are a relatively low concentration (total IgG <20g/L, IgA or IgM <10 g/L), normal blood picture, no depression of normal immunoglobulins, no urine Bence-Jones Protein. Bone marrow examination is not usually indicated but if done will show <10% plasma cells with no atypical cells.

MGUS can be regarded as a "carcinoma in situ" of the immune system and like any in situ lesion it has the capacity to progress to malignancy, quickly or slowly, or it can remain largely static for the life of the individual, hence the need for monitoring at least annually. Evolution to multiple myeloma (or macroglobulinaemia) occurs in 25% of patients.

Malignant paraproteins

These consist either of IgG or IgA (multiple myeloma) or IgM (Waldenstrom's macroglobulinaemia or lymphoma) and show the invasive characteristics of malignancy with infiltration and destruction of bone marrow.

Characteristics of a malignant, as compared with a benign paraprotein are:

� anaemia, thrombocytopenia, neutropenia � immune paresis, i.e. reduction of normal IgG, IgA and IgM � high and rising concentration of paraprotein � Bence Jones protein (free light chains) typically appears in the urine in

myeloma. � myeloma causes diffuse osteoporosis or lytic lesions, either of which

can cause back pain, compression fractures or bone pain in other parts of the body

such as ribs or pelvis. � hypercalcaemia, raised ALP


� renal impairment � hyperviscosity syndrome, particularly with macroglobulinaemia

Bone marrow examination and skeletal survey establish the diagnosis.

Where there is a strong clinical suspicion of myeloma (pancytopenia, osteolytic lesions, bone pain, immune paresis) but no serum M band, urine EPP may show Bence Jones myeloma in which the band (of free light chains) is found only in urine.


Treatment of myeloma

Asymptomatic or stable myeloma does not benefit from early therapy which is indicated only for progressive disease with symptoms. Treatment involves the use of alkylating agents such as melphalan with a trend in younger (<55 years) patients to high dose therapy with autologous bone marrow transplantation.

B. Polyclonal increases or decreases in immunoglobulins

Polyclonal increases

These are reflected in serum proteins as an increase in total globulins and in the EPP as an increased density in the gamma zone.

They are caused by any chronic inflammatory or liver disorder:

� chronic hepatitis, viral, alcoholic or autoimmune � connective tissue diseases � chronic inflammatory bowel or pulmonary disease � parasitic infestations

Pacific Islanders and South East Asians almost invariably show a moderate polyclonal increase in immunoglobulins reflecting exposure to a different range of microbiological antigens compared with temperate climates.


In two conditions a single immunoglobulin is markedly elevated:

� IgG in chronic active autoimmune hepatitis � IgM in autoimmune biliary cirrhosis

Polyclonal decreases

There are three main syndromes -

Acquired idiopathic hypogammaglobulinaemia This can occur in childhood or adult life, is associated with recurrent bacterial infections and can be of all degrees of severity. Sometimes it is transient; associated with recent viral infection.

Secondary hypogammaglobulinaemias (immune paresis) These are usually secondary to chronic lymphatic leukaemia, multiple myeloma, macroglobulinaemia, lymphomas or nephrotic syndrome.

Selective IgA deficiency This is common (1:700) and usually asymptomatic. Sometimes it is associated with coeliac disease, allergies, respiratory infections, or autoimmune disorders.

Imprecision

A word now replacing the older term "precision" which refers to the analytical scatter (variance) of results when a single sample is tested repeatedly. The imprecision of a test is expressed as the coefficient of variation (qv).

see also Variation.


Inappropriate ADH see Sodium (Na+), serum

Indirect bilirubin see Bilirubin, conjugated (direct) and unconjugated (indirect) fractions

Infection control

see MRSA (methicillin resistant Staphylococcus aureus) Needlestick injuries

Infectious mononucleosis

specimen: � serum for heterophil antibodies, liver enzymes, EBV antibodies. � whole blood (EDTA) for blood count

Epstein-Barr Virus is the causative agent in infectious mononucleosis which is characterised by lymphadenopathy, pharyngitis, fever, variant lymphocytosis in the blood film and transient heterophil antibodies in serum. Fatigue can be profound and continue for months.

Although EBV infections are common in children, they are often mild and pass undiagnosed. The peak incidence for infectious mononucleosis is in adolescence and early adult life, but a few individuals who remain uninfected succumb in later life.


EBV, along with hepatitis A, B and C, is one of the four common causes of viral hepatitis.

Although typically immunity is secure, EB virus remains latent in a small proportion of B lymphocytes and can be reactivated in the immunosuppressed state.

Blood picture

Variant (atypical) lymphocytes appear in the film during the first week of illness increasing typically to more than 20% of the total WBC during the second week and declining over ensuing weeks.

Variant lymphocytes are found in many viral illnesses including CMV and infectious hepatitis and the protozoan illness toxoplasmosis. Because CMV and toxoplasmosis have a similar clinical picture to infectious mononucleosis, they are sometimes included in the "glandular fever syndrome".

Neutropenia and thrombocytopenia are common and occasionally an autoimmune haemolytic anaemia.

EBV can invade the liver causing elevation of liver enzymes to levels of 200-500 units/L or occasionally higher. Alkaline phosphatase and GGT often show relatively greater elevations than the AST and ALT when compared with infectious hepatitis.

Heterophile antibodies ("Paul Bunnell test")

Heterophile antibodies, so-called because they agglutinate animal as well as human red cells, appear in 90% of cases by the 3rd week of illness. After an infection they persist for 3-6 months.


A first test that is negative should be repeated in a fortnight or so. Persistently negative results can occur in cases of proven EBV infections; they are more common in the younger or older age groups and in those with severe disease. Where clinical suspicion remains despite negative heterophile antibodies, EBV antibodies should be requested.

EBV antibodies

Where EBV infection is suspected but heterophil antibodies remain negative � as happens in 10% of young adults, and 50% of children � the measurement of EBV antibodies will provide a definitive answer.

VCA (viral capsid antigen) IgM antibodies appear at 4-7 days after symptoms develop and persist for 2-4 months, occasionally up to 1 year. Their presence indicates current or recent infection.

VCA IgG antibodies appear at the same time as IgM but persist for life.

EBNA (anti EB nuclear antigen) antibodies appear 3-6 weeks after onset and also persist for life. 80% of the population are EBNA +ve, indicating past infection. A minority of people infected with EBV never develop EBNA antibodies but will have a positive VCA IgG test to indicate their past exposure.

Infertility see Amenorrhoea FSH (follicle stimulating hormone) and LH (luteinising hormone) for ovarian failure

Progesterone for confirmation of ovulation

Prolactin for hyperprolactinaemia

Polycystic ovary syndrome (PCOS)


Seminal fluid

Influenza

Virus can be recovered from a posterior pharyngeal swab during the first 3 days of illness. The swab must be placed in viral transport medium and transported on ice. Antibodies can be measured in paired sera.

Inorganic phosphorus see Phosphate

INR (international normalised ratio)

The INR is the test used to monitor warfarin anticoagulant therapy which is being increasingly widely used across the range of thromboembolic disease. Warfarin is a vitamin K antagonist and acts by reducing levels of Factors II (prothrombin) VII, IX and X. The INR is a standardised prothrombin ratio calibrated so that INR results from one laboratory are directly comparable with those from another.

A. Warfarin dosing regimens

The ½-life of warfarin is 36 hours and those of Factors II, VII, IX and X vary between 7 and 60 hours and for this reason, response to a dose change is slow with a lag of 3-4 days before a new equilibrium is achieved.


Although the INR is often requested as a semi-urgent test so that specimen collection, testing, reporting and dose change can all be done on the same day, the 3-4 day lag in INR response makes this urgency unnecessary. Dose changes can wait till the next day.

1. Standard warfarin regimen for rapid anticoagulation.

Standard dosing regimen:day INR Warfarin dose (mg)

1 <1.4 10 (5 in older patients)2 <1.8 53 <2.0 5

2.0-2.2 52.3-2.4 42.5-2.7 32.8-3.0 23.1-3.5 1>3.5 —

predictedmaintenance dose

4 <1.4 >81.4-1.7 6-81.8-2.3 52.4-3.0 43.1-3.5 <33.6-4.0 <2

Note: If 3.6-4.0, miss next day's dose, then give 2.0 mg. If >4.1, miss 2 days' doses, then give 1.0 mg.


2. Alternative slower regimen Can be used in older outpatients with chronic atrial fibrillation (except

when on amiodarone). Day INR Warfarin dose Time to next

(mg) change/INR

Day 1 <1.4 3 mg 1 weekDay 8 <1.8 4 mg 1 week

1.8 - 2.5 3 mg 2 weeks2.5 - 4.0 2 mg 1 week

>4.0 specialist 1-3 daysadvice (depending

on INR level)

B. Target INR

The recommended target in the table below is a guide only and in selected patients a different level may be recommended.

Indication Recommended INRTarget

DVT prophylaxis in high risk situations 2 - 3Treatment of VTE 2 - 3Prevention of systemic embolism: 2 - 3

atrial fibrillationvalvular heart diseasefollowing mycocardial infarctiontissue heart valves (<3 months)

Mechanical bileaflet or tilting disc heart valve. 2.5 - 3.5- older caged ball valve may need higher targetRecurrent thrombosis on Warfarin 3.0 - 4.0 (?)Thrombosis in antiphospholipid syndrome 3.0 - 4.0 (?)


C. Excessive INR Respon Sometimes a patient with a stable INR shows a marked change. Possible causes are:

• incorrect dosage (often associated with a prescription change) accounts for half of these unexpected changes.

• drugs

antibiotics cardiac anti- gastrointestinalinflammatory

cotrimoxazole amiodarone phenylbutazone omeprazoleerythromycin clofibrate piroxicam cimetidinefluconazole propanolol paracetamolmiconazole sulfinpyrazonemetronidazoleisoniazid

• gastrointestinal disease � diarrhoea • hepatic disease, congestive cardiac failure

Bleeding risk while on warfarin

Composite figures for overall risks:

fatal bleeding 0.25% major bleeding 1-3% minor bleeding 6-7%

INR level v patient bleeding risk


INR events/100 estimated riskpt years over 48hr period

2 - 2.9 4.8 1 in 4,0003 - 4.4 9.5 1 in 2,000

4.5 - 6.9 40 1 in 500>7.0 200 1 in 100

D. Management of overcoagulation

The urgency of correcting a high INR (above 4 if the target is 2.5) will depend on whether there is any bleeding and whether major or minor.

Therapeutic options are:

1. For all high INR's: Stop warfarin, then restart at a lowered dose when INR is higher than

target but <5.

INR % dose reduction Usual number (days)of omitted doses

4 - 5 25 05 - 6 25 16 - 8 33 2>8 50 3

2. Vitamin K

Low dose vitamin K replacement (usually 1-2 mg initially) is used where the INR is excessively prolonged by warfarin as a consequence of vitamin K depletion. Replacement of vitamin K stores should make the subsequent response to warfarin more predictable. Vitamin K is usually administered orally or sc, occasionally IV. For oral


replacement the appropriate volume can be drawn up into a tuberculin syringe from an ampoule (1 mg/0.5ml or 10 mg/ml) of vitamin K in a dose of 0.5-2 mg (see below). Larger doses of vitamin K (e.g. 5-10 mg) may make the patient resistant to further warfarin.

3. Prothrombin complex concentrate

Prothrombinex 25 u/kg or FFP 15 mls/kg is given for immediate correction when there is major bleeding.

Guidelines for severe overcoagulation

clinical guidelineINR 6-8 without bleeding • stop warfarin

• restart in reduced dose when INR <5• give 0.5-1mg oral/sc vitamin K if INR

fails to shorten, or if reversal required within 24-48 hrs.

INR >8 with bleeding • stop warfarin• restart in reduced dose when INR <5.• give 1-2 mg oral/sc vitamin K (repeat

in 24hrs if necessary).

High INR and major bleeding • stop warfarin• admit to hospital.• give vitamin K 5 mg sc/iv.• give prothrombin complex concentrate

(prothrombinex) 25 units/kg or FFP 15 mls/kg.

Insecticides see Organophosphate toxicity Cholinesterase Carbamates


Insulin

specimen: serum or plasma (EDTA or heparin)The specimen needs to be stored at 4ºC and separated in less than 4 hours. A fluoride specimen for plasma glucose is collected at the same time.

ref. range: 5 - 13 mU/L (fasting).

The principal use of insulin levels is in the investigation of fasting hypoglycaemia (glucose <3.0 mmol/L) due to insulinoma or undeclared use of sulphonylureas or insulin.

Insulin-like growth factor 1 see IGF-1 (insulin-like growth factor-1, somatomedin C)

Intestinal biopsy for enzymes see Disaccharidases

Intrinsic factor antibodies specimen: serum


80% of pernicious anaemias give a positive test. False positives are infrequent.

Iron specimen: serumref. range: child 7-21 µmol/L

adult 10-30 µmol/L

Serum iron levels show a marked diurnal variation with morning levels higher by 30%.

They are also rapidly depressed to low levels by acute or chronic infections or any other chronic disorder.

Because of these large fluctuations, serum iron is of little diagnostic use on its own but when combined with iron-binding capacity/transferrin and ferritin, total body iron deficiency or excess can usually be defined.

Serum iron is elevated by:

• oral or parenteral iron supplements

• haemochromatosis

• alcohol

• hepatitis

• oestrogens/oral contraceptives

• iron poisoning � children absorb oral iron easily and in acute poisoning can present with levels in the 100-500 µmol/L range.

Iron-binding capacity (IBC) and saturation


specimen: serumref. range: IBC: 45-72 µmol/L

saturation: 20-40% (or 0.20-0.40)

saturation Fe

IBCx= 100%

IBC and saturation are routinely done with requests for iron. IBC reflects the iron transport protein transferrin, a globulin travelling in the beta band on electrophoresis.

Transferrin (and IBC) are elevated by:

• iron deficiency

• oestrogens, oral contraceptives and pregnancy, to an upper level of about 90 µmol/L

• hypothyroidism

• ineffective erythropoiesis e.g. B12, folate deficiency

Transferrin is a negative acute phase reactant and is reduced by chronic inflammatory disease, malignancy, renal disease, thyrotoxicosis, and haemochromatosis.

The two main indications for measuring IBC/transferrin are:

• haemochromatosis (qv) in which saturation is typically above 60% when the disease becomes symptomatic.

• in the investigation of iron deficiency when a serum ferritin is not available or has been elevated by coexisting inflammatory or liver disease.


Iron deficiency Useful tests• ferritin the most sensitive and specific test. If low it is almost

pathognomonic of iron deficiency, latent or overt, but a normal result does not exclude iron deficiency ascoexisting inflammatory disease can elevate ferritinindependently

• MCV & MCH reduced, but not until ferritin is <10• Hb reduced, but anaemia develops later than

the other changes• blood film oval cells, hypochromia, microcytosis• iron reduced, but many other conditions cause

a fall in serum iron• IBC increased (may be normal if inflammation coexists)• % saturation reduced

Aetiology of iron deficiency

The treatment of iron deficiency must always be accompanied by a search for the cause. Deficiency is so common in women of child-bearing age that it is easy to attribute all deficiencies in women to menstrual loss while forgetting this is not possible after the menopause � nor in males of any age. Deficiencies fall into three broad groups.

Chronic blood loss


female genital tract:• menstrual loss• pregnancies• tumours of female genital tract with abnormal bleeding

gastrointestinal loss:• oesophagus, stomach, duodenum – peptic ulcer,

NSAIDS, hiatus hernia,varices• large bowel – tumours (iron deficiency is a common

presentation), ulcerative colitis, haemorrhoids• small bowel – hookworm, congenital vascular

malformations, Meckel's diverticulum

other:• epistaxis, haematuria, haemoptysis, telangiectasia

Dietary insufficiency Mainly in infants, adolescents and the elderly.

Malabsorption Coeliac disease particularly.

Iron deficiency in athletes Iron deficiency is more common in athletes for three reasons:

� they may be on relatively low iron diets � they frequently suffer occult gastrointestinal blood loss � they may suffer march haemoblobinuria with urinary iron loss

For these reasons many athletes take oral iron supplements when their ferritins are towards the lower end of the reference range.


Iron saturation see Iron saturation

Islet cell antibodies (ICA) ICA precede the development of Type I diabetes (IDDM) by a variable period of years and have been used for predicting risk in relatives of Type 1s and in population studies.

They are measured in JDF units

>80 units or above almost invariably associated with development of IDDM, usually within 10 years.

40 units moderate to high risk 20 units low to moderate risk 5-20 units low risk. These levels may disappear; may persist without

progression; or may progress to IDDM.

ITP (idiopathic immune thrombocytopenic purpura)

A relatively common autoimmune disorder characterised by an isolated thrombocytopenia in the absence of drugs, chemicals or any haematological or non-haematological disorder.

Acute immune thrombocytopenia is distinguished from acute viral thrombocytopenia by the clinical course with the latter usually recovering within a few days without the requirement for specific therapy. Chronic immune thrombocytopenia is diagnosed


when the thrombocytopenia persists for more than 6 months. It may have a viral trigger, occur as part of an autoimmune disorder (e.g. SLE), arise in association with a lymphoproliferative disease or as an idiopathic finding.

ITP is usually a diagnosis of exclusion. Appropriate investigations may include a coagulation screen with bleeding time (to evaluate a possible associated platelet dysfunction), autoimmune investigations (ANA, anti DNA rheumatoid factor, anticardiolipin antibodies, platelet antibodies), lupus anticoagulant screen, protein electrophoresis and immunoglobulins, HIV.

Treatment is either with prednisone or intravenous immunoglobulin, particularly when the platelets fall below 20 109x L/ .

see Thrombocytopenia

IUCD see Actinomyces

J


Jaundice

Hyperbilirubinaemia becomes visible in the skin and sclera of most individuals when the bilirubin is above 40 µg/L. The skin is yellow in carotenaemia also, but not the sclera.


Liver enzymes


Carotene

Joint aspirate see Synovial aspirate

K

K+ (kalium) see Potassium (K+), serum

Karyotype

The number and structure of an individual's chromosomes see Chromosome analysis


Ketones

specimen: random urine or serum

This test, which is part of routine urinalysis, is usually done by a dipstick method. Mild positives occur with starvation or illness. Moderate or strong positives in Type I diabetics indicate poor control requiring additional insulin and rehydration - urgently if there is significant acidosis.

"Ketostix" detects acetoacetate which accounts for only a small percentage of "ketone bodies", the greater portion being beta-hydroxy-butyrate (qv).

Klebsiella pneumoniae

An aerobic gram-negative enteric bacillus. Found on mucosal surfaces and in the faeces of about 5% of healthy people. It occasionally causes pneumonia as well as biliary and urinary tract infections.

Kleihauer stain for HbF see Thalassaemias

Klinefelter syndrome

XXY is the usual karyotype. Testosterone levels are typically reduced and FSH and LH increased. Other pituitary tests are usually normal.


Clinically, patients are often unusually tall with long legs. Testes are small, pubic hair scant and there may be gynaecomastia.

L

Laboratory error see Errors Variation

Lactase deficiency see Disaccharidases Reducing substances in faeces Lactose tolerance test (LTT)


Lactate dehydrogenase see LD (lactate dehydrogenase)

Lactose intolerance in infants see Reducing substances in faeces

Lactose tolerance test (LTT)

Protocol A fasting blood glucose is taken and then a loading dose of lactose is given, 1.5g/kg to a maximum of 50g and blood samples taken each quarter hour for 1 hour with a final sample at 2 hrs. The test cannot be used in diabetics.

Interpretation In a normal person, s. glucose (derived from the lactose) rises more than 1 mmol/L above the fasting level, usually peaking at 15 or 30 mins. Because of its indifferent sensitivity and specificity, the LTT is not often performed.

Acquired lactase deficiency in adults is not uncommon, usually secondary to malabsorption syndromes, Crohn's disease, giardiasis, bacterial gut infections etc. Trial of a lactose-free diet can assist with the diagnosis.

Lag storage GTT


see GTT

Laxative abuse screen specimen: 50 ml random urine

The method detects only stimulant laxatives.

LD (lactate dehydrogenase) specimen: serum

ref. range: 120 - 250 IU/L

LD is an enzyme of low specificity found in liver, myocardium, skeletal muscle and red cells. It is also found in some malignancies, notably lymphomas and particularly non-Hodgkin's lymphoma.

Elevations can be due to:

• lymphomas, up to 2-3x the upper limit of the reference range. The level gives an estimate of tumour bulk.

• other tumours, especially germ cell

• myocardial infarction, increase commences 12-24 hrs after infarction, disappearing after 7-12 days

• megaloblastic anaemias due to B12 or folate deficiency

• haemolytic anaemia

• artefactual haemolysis due to faulty specimen storage or collection

• liver disease, particularly hepatitis

• skeletal muscle damage


Of the LD isoenzymes, LD1 is derived from myocardium or erythrocytes, LD5 from liver.

LDH see LD (lactate dehydrogenase)

LDL cholesterol see Cholesterol LDL cholesterol

Lead, blood specimen: whole blood (EDTA)

ref. range: normal: adults <0.7 µmol/L whole bloodchildren <0.5 µmol/L whole blood

toxic: adults >3.7 µmol/L whole bloodchildren >2.2 µmol/L whole blood

Industrial workers exposed to lead are put off work if their blood lead is >3.2 on one occasion or >2.6 on three consecutive occasions.

Domestic exposure occurs when old lead-based paints are being sanded or burnt off. Children are at risk when they ingest paint fragments or dust; as are pets when they lick their fur.


High levels should be repeated in 3-4 weeks.

Lead poisoning interferes with porphyrin metabolism causing elevation of urinary coproporphyrin, PBG and ALA. The porphyrin changes are a better indicator of toxicity than the blood lead on its own but are not used for routine industrial testing. Red cells may show basophilic stippling.

Lead, urine specimen: 24-hr urine in special container with added HCl

ref. range: <0.25 µmol/day

Urine leads are used for monitoring chelation therapy in lead poisoning after the diagnosis has been established using blood lead levels.

LE cells ANA and anti-DNA (qv) antibodies have replaced this test in the diagnosis of SLE.

Legionella specimen: sputum for culture

serum for antibodiesref. range: antibody level

There are more than 30 species of Legionella, the cause of Legionnaire's disease.


The organism, is found in hot water systems or the humidified air of air-conditioning systems, causing both sporadic cases and institutional outbreaks of atypical pneumonia. Since the disease was first described in New Zealand in 1980 there have been about 700 cases. In two New Zealand studies it was the cause of 5-10% of community acquired pneumonia.

Culture is the diagnostic method of choice. Legionella culture must be asked for specifically as it requires the use of specially prepared media. Specimens contaminated with sodium e.g. saline-induced sputum and bronchial washings, are not suitable for Legionella culture.

Most healthy adults have an antibody titre of <1.128. Rising antibodies in paired sera provide good evidence of active infection. Paired sera should ideally be collected two weeks apart.

Please consult microbiologist for suspected infections.

Leprosy

Diagnosis is by identification of acid-fast bacilli in histological sections or in scrapings from incised lesions or nasal septum.

Please consult microbiologist if tests are required.

Leptospirosis specimen: serum

Since vaccination of cattle was introduced several years ago, the incidence of leptospirosis has dropped to the point where it is now rare in Auckland and


uncommon in New Zealand, <2 cases/105. Host animals include cattle, pigs, horses and rodents. Human infection typically follows exposure to blood of infected animals or water contaminated with their urine.

For diagnosis an antibody screen test is performed followed by (on sera that are positive) specific agglutination testing against the common strains of leptospira.

Titres of 1:200-1:400 are borderline.

After infection, titres rise sharply into the thousands in those who have been infected in the past. The highest titre may not indicate the cause of the latest illness.

Consultation with the microbiologist is suggested when acute leptospirosis is a possibility so that blood culture in special medium can be arranged.

Leucocyte count see Blood count

Leucocytosis Refers to an increase in the total white cell count. Its significance depends on which cell type is increased.

see Neutrophils (polymorphs) Lymphocytes Monocytes Eosinophils


Leuco-erythroblastic blood picture

Immature myeloid cells (myelocytes, metamyelocytes, band neutrophils), and immature red cells (nucleated red cells), are present due to invasion or disturbance of the normal marrow. Causes include:

• metastatic malignancy

• primary haematological malignancy

• myelofibrosis

• acute haemolysis

• thalassaemia major, especially after splenectomy

Leukaemias see Acute leukaemias, Chronic myeloid leukaemia (CML)

Leukaemoid reaction

A peripheral blood picture resembling leukaemia in a patient who does not have leukaemia. The increased numbers of white cells can be of either lymphoid or myeloid type. Atypical response to infection in a child is the commonest cause. It is seen particularly in Down's syndrome. Other causes include non-haematological malignancies and acute haemolysis.

LFT (liver function tests)


see Liver enzymes

LH (luteinising hormone) see FSH (follicle stimulating hormone) and LH (luteinising hormone)

Light chains in urine see Bence Jones protein (BJP)

Lignocaine see Antiarrhythmic drugs

Lipaemia

After a fat-containing meal, and in the primary or secondary hypertriglyceridaemias, the serum is turbid or creamy due to fat particles. A severe degree of lipaemia can cause technical interference with some tests to the point where they become invalid.

see also Triglyceride


Lipase

A test used in some centres in addition to amylase in the diagnosis of acute pancreatitis.

Lipid disorders

When classifying a lipid disorder for the purposes of treatment, two questions need to be asked:

• is it a primary lipid disorder or secondary to some other metabolic abnormality?

• which lipid fractions are elevated - cholesterol only - cholesterol and triglyceride - triglyceride only

Secondary disorders

These are easily identified and when treated may entirely correct the lipid abnormalities.

The common causes are:

• obesity

• alcohol

• diabetes


• hypothyroidism


• liver disease

• drugs: oestrogens, oral contraceptives, beta blockers, corticosteroids, thiazides, isotretinoin, antivirals, valproate

Primary disorders

If no secondary causes are identified the disorder is presumed to be primary. There is a range of familial disorders which are presumptively identified by the family history or by physical signs such as xanthomata, corneal arcus.

The commonest familial disorders are familial hypercholesterolaemia and familial combined hyperlipidaemia. There are many others.

However, the commonest primary dyslipidaemia by a wide margin is polygenic hypercholesterolaemia, which is not familial. It is identified mainly by exclusion � no significant family history, no abnormal physical signs. Presumed to result from a combination of genetic and environmental factors, it provides a convenient diagnostic refuge.

Which lipid fractions are elevated?

Defining the abnormal fractions is important in both diagnosis and treatment.

The feature of familial hypercholesterolaemia is very high serum cholesterol.

The familial elevation of familial combined hyperlipidaemia may be cholesterol only (1/3), triglyceride only (1/3), or both (1/3).

Causes of secondary dyslipidaemias do not reliably produce a constant picture. For example, though hypothyroidism typically causes elevation of cholesterol only, it can at times raise the triglyceride also.


Treatment

Dietary modification is common to the treatment of all dyslipidaemias.

Drug treatment, if required, will depend on whether the abnormality is cholesterol only (statins being the agent of choice), triglyceride only (fibrates usually first choice) or both.

Lipid tests

A "fasting lipid screen" consists of:

NHF ideal leveltotal cholesterol <5.0HDL cholesterol >1.0LDL cholesterol <3.0fasting triglyceride <2.0total/HDL ratio <4.5

NHF = National Heart Foundation

see Cholesterol Triglyceride Lipoproteins

Lipoproteins

In serum, lipids are carried as lipoprotein particles which are grouped in four fractions:


Lipoprotein Cholesterol Triglyceridefractionchylomicrons small ++++LDL ++++ smallVLDL/IDL ++ ++++HDL ++ small

Diagnosis of the hyperlipoproteinaemias requires a fasting specimen to eliminate the contribution of dietary triglyceride in both chylomicrons and the VLDL fraction.

Hyperlipoproteinaemias can be familial or secondary (see separate entries under triglyceride and cholesterol for aetiology of the secondary disorders) or, commonly, a mixture of both. Occasionally the diagnosis is obvious, e.g. the clear-cut familial hypercholesterolaemias causing severe coronary artery disease in early adult life � but most of the common hypercholesterolaemias and hypertriglyceridaemias are part of a large amorphous population, deeply affected by diet and life-style and mixed inextricably with the "normal" population, whoever they are.

Typing of hyperlipoproteinaemias

The WHO classification is that of Fredericksen who recognised six types: I, IIa, IIb, III, IV, V. The classification has limitations. Familial hyperlipoproteinaemias can present as different types in different family members. A single aetiology (e.g. hypothyroidism) can be associated with several types. Treatment can convert one type to another. Nevertheless the terms are still used. Types II and IV, and to a lesser extent V, are the commonest.

IIa IIb IV Vtotal cholesterol +++ +++ + +triglyceride n ++ +++ +++LDL cholesterol ++ ++ n nVLDL cholesterol n + +++ ++chylomicrons - - - ++turbid serum - ++ ++ ++


Note that the classification does not use HDL cholesterol.

see also Apolipoproteins

Lipoprotein electrophoresis

Cholesterol

Triglyceride

Lipid disorders

Lipoprotein (a) specimen: serum

ref. range: <300 mg/L

Lipoprotein (a), not to be confused with apolipoprotein A which is the protein component of HDL, is an independent risk factor for coronary artery disease (CAD). It can be of particular interest in patients whose CAD is not explained by other risk factors.

Levels are largely genetically determined but tend to rise after the menopause or with renal impairment. Fasting, exercise or statins have little effect. Levels may be lowered by niacin and perhaps by fibrates. Acute illness can have an effect andlipoprotein (a) should not be measured within 3 months of a myocardial infarction.

Lipoprotein electrophoresis specimen: serum

Four fractions are identified:


alpha-I contains HDL

pre-beta contains VLDL, elevated in Type IV, IIb or III

beta contains LDL, elevated in Type IIa or Iib

chylomicrons found in non-fasting serum or Type V

Lipid EPP is a specialist investigation. For most clinical purposes a lipid abnormality is defined by quantitation of cholesterol fractions and triglyceride on a fasting specimen.

Listeria monocytogenes

specimen: blood cultures, CSF, for acute infection stool for carrier state

Listeria, an aerobic gram-positive bacillus, is widely distributed in soil, water and many animals. It is occasionally found in the human gastrointestinal tract. Spread to humans is mainly via contaminated food. Food borne outbreaks due to contaminated coleslaw, milk, soft cheese and mussels have been reported. Although most infections are mild and harmless, septicaemic infection in pregnant women, presenting as a flu-like illness, may lead to serious foetal infection leading to still-birth or neonatal meningitis. Immunocompromised persons and the elderly are also at risk of invasive disease.

Treatment is penicillin (or amoxycillin) with or without gentamicin. Erythromycin or cotrimoxazole are less desirable alternatives. Treatment should be for at least 14 days. L. monocytogenes is resistant to all cephalosporins.

Lithium


specimen: serumtherapeutic range: mmol/L 12 hrs post-dose

0.4-0.9 desired range1.0-1.5 sometimes toxic>1.5 usually toxic

The specimen must be taken 12 hours after the last dose. Steady state levels are achieved 2-5 days after a dose change, or longer in older patients with renal impairment. When lithium is stopped, the level falls with a ½-life of 1-3 days.

Because of the high incidence of toxic effects, monitoring is regarded as essential every 3 months, and more often if clinically indicated. Base-line TSH, T4, and creatinine levels should be measured before commencing therapy and 6 to 12 monthly thereafter.

Manifestations of toxicity

• a wide range of CNS and GI effects

• hypothyroidism � relatively common

• nephrogenic diabetes insipidus

• serum potassium maybe elevated

• renal damage with raised s. creatinine may occur when serum levels have been consistently in the toxic range over a long period.

• high serum calcium

• cardiac toxicity: AV block, T wave changes, premature ventricular contractions.

Drugs that elevate lithium: diuretics NSAIDs metronidazole ACE inhibitors


Liver enzymes specimen: serum

ref. ranges: see under individual constituents

General

ALP and GGT are the cholestatic enzymes so are particularly elevated in:

• biliary obstruction by gallstone or carcinoma of head of pancreas

• secondary or primary carcinoma of the liver

• drugs causing cholestasis AST and ALT are the hepatocellular enzymes and are particularly elevated in viral hepatitis.

Non-specific elevations of liver enzymes

Typical presentations of a disease are easily diagnosed but a common problem is finding unexpected elevations of one or more liver enzymes. For any single aetiology, the enzyme patterns may vary from what is usually described as typical. With alcohol, for example, GGT is said to be affected particularly, but not infrequently one of the others is raised on its own, or any two of them, or all.

Here is a checklist, not exhaustive, of aetiologies to be considered. Many of these conditions are described in more detail under their own alphabetic listings.

1. acute viral hepatitis � hepatitis A � hepatitis B � hepatitis C


� infectious mononucleosis � CMV and other viruses causing an acute viral syndrome

2. chronic viral hepatitis � hepatitis B � hepatitis C � HIV 3. other infections � malaria � leptospirosis � typhoid � TB � brucellosis

4. drugs - the list includes: � analgesics salicylates paracetamol propoxyphene � antibiotics erythromycin estolate tetracyclines flucloxacillin amoxycillin ± clavulanate sulphonamides � anticonvulsants phenytoin carbamazepine sodium valproate phenobarbitone � anti-TB drugs rifampicin isoniazid para-aminosalicylic acid (PAS) � hormones oestrogens


oral contraceptives androgens

� other phenothiazines halothane cytotoxic drugs allopurinol methyldopa chlorpropamide some herbal remedies

5. alcohol: affects range from minor elevation of one (classically GGT) enzyme, through

massive elevations in acute alcoholic hepatitis down to minor or no elevations in end-stage cirrhosis.

6. obesity: elevates ALT particularly and other enzymes as fatty liver develops. 7. diabetes: enzyme elevations are common in association with poor glycaemic control,

obesity, hypertriglyceridaemia and fatty liver. 8. gall-stones: causing obstruction and cholangitis 9. malignancy: � metastases from a distant primary � carcinoma head of pancreas causing obstruction � primary hepatic malignancy 10. autoimmune liver disease: � autoimmune hepatitis (formerly chronic active hepatitis)


� primary biliary cirrhosis � sclerosing cholangitis

11. other chronic inflammatory disease: � SLE � rheumatoid arthritis - raised ALP � ulcerative colitis � Crohn's disease 12. haemochromatosis 13. heart failure with hepatic congestion 14. muscle disease: AST and ALT rise when CK is substantially elevated.

15 Wilson's disease 16. industrial or other toxins 17. isolated non-hepatic elevations of ALP � see alkaline phosphatase 18. macro-molecular enzyme variants: the enzyme molecule is too large to leave the circulation via the glomerulus

with the result that an enzyme level is permanently elevated in the absence of any disease process.

19. idiopathic benign elevations: when no other explanation can be found.


Summary

It is a matter of clinical judgement how many tests should be done as investigations for these conditions.

� if the patient has a symptomatic illness an answer needs to be found

� ultrasound is mandatory where obstructive or malignant disease is a possibility

� a screen for chronic asymptomatic enzyme elevations might include:-

• hepatitis B surface antigen

• hepatitis C antibodies

• glucose (diabetes)

• TSH (hyper- or hypothyroidism)

• lipids (hyperlipidaemia, fatty liver)

• iron, IBC, % saturation, ferritin (haemochromatosis)

• smooth muscle antibodies (autoimmune hepatitis)

• anti-mitochondrial antibodies (primary biliary cirrhosis)

• CK (skeletal muscle disease)

• immunoglobulins

� serial tests over weeks, months or years will define the time-course of the underlying process. Is it:

• progressive (e.g. malignancy)?

• constant or oscillating about a mean (e.g. alcohol, chronic hepatitis)?

• returning to normal (e.g. resolving hepatitis or a drug effect when the drug is stopped)?


Even after all this there may be no answer. Repeat tests at least yearly,or earlier if the clinical picture changes. If the patient is clinically well, classify it as idiopathic meanwhile. There seem to be quite a lot of these around.

Liver-kidney microsomal (LKM) auto-antibodies

specimen: serum

LKM antibodies are sometimes found in autoimmune hepatitis.

LKM antibodies

see Liver-kidney microsomal (LKM) auto-antibodies

Low density lipoproteins (LDL) see Cholesterol

Lipoproteins

Low molecular weight heparin (LMWH)

see Heparin therapy


LSD (lysergic acid diethylamide)

specimen: random urine, no preservative range: a result is reported positive if above a cut-off level of 0.5 ng/ml

Chlorpromazine ingestion will give a false positive result.

Lupus anticoagulant (LAC)

The lupus anticoagulant is an acquired coagulation inhibitor which is associated with SLE and thromboembolic disorders. It is associated, but not synomynous with, cardiolipin (qv) antibodies. In the context of thrombotic disease or recurrent abortions, a positive lupus anticoagulant detected on two occasions at least three months apart, with or without anticardiolipin antibodies, defines an antiphospholipid antibody syndrome. Anticardiolipin antibodies are sometimes found transiently in healthy people.

The APTT is prolonged in patients with LAC and fails to correct in the APTT 1+1 test.

The tests performed routinely as the LAC screen are KCT (Kaolin Clotting time), APTT, PR, DRVVT (dilute Russell's viper venom time) and DTTA (dilute tissue thromboplastin assay).

Luteinising hormone (LH) see FSH (follicle stimulating hormone) and LH (luteinising hormone)


Lyme disease see Borrelia

Lymph node histology and cytology

Where malignant lymphoma is suspected, cytology imprints are useful in addition to the formalin-fixed specimen.

• Lymph node imprints These may be made at the time of surgery by bisecting the node and gently placing the cut surface for a few seconds on a glass slide. Up to four slides should be imprinted. Pressure should not be applied and the resulting imprints should be allowed to air-dry for 15 minutes.

After air drying, the imprint slides should have the patient's name written in pencil on the frosted end and be placed in a cytology request envelope or other envelope.

• Tissue specimen Half of the bisected node should be placed in 10%

formal saline while the remaining half should be placed in normal saline.

Lymphocyte antibodies

specimen: serum

Please give details of previous transfusions or transplant.


T-lymphocyte count in HIV see CD4 T-lymphocytes

Lymphocytes

Lymphocytes play a central role in the immune response. The two main types of cell, identified by cell marker studies are:-

T cells, primarily responsible for cell-mediated immunity

B cells, primarily responsible for humoral immunity (immunoglobulin production).

Lymphocytes are also classified by their CD (cluster designation) number. For example,CD4 (qv) cells are T cells used as a marker for immune system damage in HIV infections.

Lymphocytosis An absolute lymphocytosis (>4.0 x 109/L) is typically found in two situations.

• viral infections, particularly infectious mononucleosis, acute viral hepatitis and CMV infections.

• CLL (chronic lymphatic leukaemia), in which the proliferating lymphocytes are monoclonal B cells with light chain restriction. CLL should always be suspected when there is an unexplained progressive lymphocytosis at or beyond middle age.

Lymphopenia


Causes include:

• viral illnesses

• pancytopenia due to any cause

• advanced Hodgkin's disease

• congestive heart failure

• steroid therapy

• AIDS

Variant lymphocytes

These cells, also called reactive lymphocytes, transformed lymphocytes or atypical lymphocytes, are small lymphocytes which have undergone antigenic stimulation (e.g. by a virus) that has transformed them into larger cells readily recognised in a blood film. The commonest causes of variant lymphocytes are:

• infectious mononucleosis (EBV) • acute viral hepatitis A, B or C • CMV infections • toxoplasmosis

Less common causes are:

� other viral infections � immune disorders � chronic non-viral infections

M


M-band see Immunoglobulins, IgA, IgG, IgM: Monoclonal bands Macroglobulinaemia Multiple myeloma

Macrocytosis

Macrocytes are red cells with an MCV (mean cell volume) be divided into three groups:

1. The megaloblastic macrocytic anaemias These are distinguished by the presence of megaloblasts in the bone marrow as precursors of the peripheral blood macrocytes. Megaloblastic anaemias are due to B12 or folate deficiency. The macrocytes are oval in shape rather than round. With well-established deficiency there are hypersegmented neutrophils, neutropenia and thrombocytopenia.

see also Folate (folic acid), serum

Vitamin B12

2. Macrocytosis due to reticulocytosis Reticulocytes are somewhat larger than older red cells. They are an

important feature of haemolytic and post-haemorrhagic anaemias. 3. Other In this large group of normoblastic processes, the macrocytes are round. The

list includes:

- alcoholism


- liver disease - hypothyroidism - malignant infiltration - cytotoxic drugs (especially hydroxyurea) - myeloma - aplastic anaemia - myelodysplastic syndromes - chronic obstructive airways disease

Macroglobulinaemia

IgM paraproteins are present in three conditions:

Benign IgM paraproteinaemia The commonest cause. The blood picture is normal, the patient asymptomatic and IgM levels are static and usually <10g/L.

Waldenstrom's macroglobulinaemia A malignant process in which the IgM band is heavy, the blood picture is abnormal and the marrow infiltrated with abnormal plasmacytoid lymphocytes.

Malignant lymphoma or CLL (chronic lymphatic leukaemia) These should always be searched for clinically, and on the blood film, when an IgM paraprotein is found.

see also Immunoglobulins, IgA, IgG, IgM

Magnesium (Mg) specimen: serum


ref. range: 0.7�1.0 mmol/L

decreased by

• excessive loss of fluid and electrolytes, diarrhoea etc. • inadequate intake : inadequate parenteral nutrition, low levels in diet and

water, (very uncommon) malabsorption • drugs diuretics, aminoglycosides, digoxin, cytotoxics, laxative abuse • alcoholism • endocrine : hyperthyroidism, hyperparathyroidism, diabetic ketoacidosis,

SIADH • hypokalaemia • redistribution of Mg into cells, e.g. alkalosis, acidosis, severe illness

increased by

• renal insufficiency • dehydration • Addison's disease • haemolysis Severe magnesium deficiency affects neuromuscular function and the cardiac conduction system. Clinically this can be manifested as tetany, convulsions, cardiac arrest. Epidemiologically, magnesium deficiency in water supplies has been linked to cardiac dysrhythmias and myocardial infarction.

Malabsorption

The aetiology of malabsorption can be considered under four headings:-


� mucosal defects � coeliac disease, the commonest cause� Crohn's disease� severe lactose intolerance

� pancreatic disease � cystic fibrosis� chronic pancreatitis

� post-infectious – Giardia malabsorption � tropical diarrhoea

� previous gastro-intestinal surgery onstomach or small bowel

Malabsorption particularly involves iron, folic acid, vitamin B12, vitamin K, vitamin D and fats.

Basic screen tests

• blood count, looking for macro- or microcytosis

• iron studies

• B12 and folate

• stool for Giardia and other pathogens

• INR

• gliadin and endomysial antibodies for coeliac disease

• vitamin D (25-OH-D) especially if ALP is raised

Follow-up tests

• jejunal biopsy is definitive in the diagnosis of coeliac disease

• 3-day faecal fat (qv) is used for documenting steatorrhoea and for assessing response to therapy such as pancreatic enzyme medication


Malaria specimen: whole blood (EDTA)

Malaria is endemic in:�

• the Pacific west of Fiji. This includes Papua New Guinea, the Solomon Islands, Indonesia. It does not include Fiji, Samoa, Tonga, New Caledonia, Niue, Tahiti or Hawaii.

• SE Asia and India • Africa and S. America

The diagnosis needs to be considered in any visitor to these areas with unexplained fever, sweats, headache, malaise, anaemia, abnormal liver enzymes.

Diagnosis is established by detecting parasites in thick and thin films. Serial blood specimens may be required. Leucopenia is usual but there can be leucocytosis. Variant lymphocytes are occasionally seen. Malaria can be accompanied by anaemia which may be caused by haemolysis, marrow depression or hypersplenism.

Of the four subtypes of Plasmodium, only two, P. falciparum and P. vivax, are commonly identified in New Zealand.

P. falciparum causes severe, sometimes lethal, illness.

P. vivax is less severe but can relapse.

P. ovale and P. malariae are the two less commonly found subtypes.

Treatment should be discussed with those who have experience in treating malaria.


Malassezia furfur

A fungus causing tinea versicolor (pityriasis versicolor) which shows as brown scaly patches on white skin or pale patches on dark skin. Microscopy of skin scrapings shows grape-like clusters of cells. The organism is not readily cultivated. Diagnosis is based on clinical features, direct microscopy and absence of fungal growth on culture.

Treatment is with a topical imidazole, ciclopiroxolamine or terbinafine. Oral terbinafine is not effective.

Malignant melanoma Classification

1. In situ � this is melanoma before it has invaded the dermis. It has 100% 5-year

survival. 2 Invasive radial growth phase � this is early melanoma which has invaded the superficial dermis but

still has an excellent prognosis.

3 Invasive vertical growth phase � this is melanoma which invades the dermis and may invade deeper

tissues. Prognosis is dependent mainly on tumour thickness which is reported as both Clark level and Breslow thickness. Breslow thickness is more important than Clark level. Few melanomas less than 0.76mm in thickness give rise to metastases. Other prognostic factors of importance are sex of the patient, anatomic site, mitotic rate,


histological evidence of regression and the presence of lymphocytes amongst the melanoma cells.

Mantoux see Tuberculin test (Mantoux test)

Maternal serum testing for foetal Down's syndrome and neural tube defects (NTD)

specimen: serum

Maternal testing programmes require careful pre-test discussion with the mother to explain diagnostic limitations and consideration of termination of an affected foetus.

The specimen should be collected at 15-16 weeks gestation (up to 20 weeks at latest) and ideally an ultra-sound will be performed at about the same time to confirm gestational age.

The combination of foetal age, maternal age and 2-4 maternal serum constituents are entered into a computer programme which estimates foetal risk. Maternal serum tests can include:

• AFP (alpha foetoprotein, elevated in NTD, decreased in Down's) • free ß hCG • free hCG • total hCG • unconjugated oestriol


• PAPPA (pregnancy associated plasma protein A � used only in 1st trimester screening)

First trimester screening at 9-13 weeks has been shown to be as effective as 2nd trimester screening in some centres and allows a decision to be made several weeks earlier. The result is presented as an estimated risk for discussion with the mother who may elect to proceed with amniocentesis for possible Down's syndrome or ultra-sound for NTD. Maternal serum testing detects about 60% of Down's and 80% of NTD.

Down's has an overall incidence of 1:650 pregnancies rising quickly after 35 years to 1:100 at age 40. Two thirds of Down's occur at a maternal age below age 35.

MCH (mean cell Hb) see Blood count

MCHC (mean cell Hb concentration) see Blood count

MCTD (mixed connective tissue disease)

A connective tissue disease characterised by features of SLE, systemic sclerosis and polymyositis.


Tests that will often be positive are:

ANA (95% positive) usually with a speckled pattern RF (50%) ENA, anti-RNP � a relatively specific feature

MCV (mean cell volume)

see Blood count Macrocytosis Microcytosis

MDS see Myelodysplastic syndromes (MDS)

Mean platelet volume see MPV (mean platelet volume)

Measles (morbilli, English measles, rubeola) specimen: serum

The test can be for immune status (IgG antibody) or acute illness (IgM).


IgM antibodies appear about two days after the rash and peak about 2 weeks later. IgM antibodies disappear after the acute illnesses. IgG antibodies persist for life.

Measles, German see Rubella

Megaloblastic anaemia see Macrocytosis Folate (folic acid), serum Vitamin B12

Melanin

specimen: urine, random

Melanomas sometimes produce enough melanin, or its colourless precursor melanogen, for these to be detected in urine. The urine may be either pigmented or colourless when first passed but darkens on exposure to air and sunlight.

MEN (multiple endocrine neoplasia)

These are familial clusters of endocrine adenomas or hyperplasias:


Type I parathyroid adenoma (95%) pancreatic islet cell adenoma or hyperplasia (80%) pituitary adenoma (50%)

Type II medullary thyroid carcinoma (95%) phaeochromocytoma (50%) parathyroid adenoma/hyperplasia (40%)

Meningitis Patients with suspected meningitis belong in hospital but if you have a CSF which might show infection, please notify us so that it can be handled urgently.

see Neisseria

Menopause

The term menopause refers to cessation of menses, a diagnosis that can be made only in retrospect.

The interval between regular menstrual cycles and the menopause is the peri-menopause, usually of about 2-3 years duration and variably associated with symptoms of reduced oestrogen secretion.

Although fertility is greatly reduced during the peri-menopause, occasional ovulatory cycles occur with FSH and LH at normal levels. During the post-menopausal period the FSH is consistently elevated into the 20-120 IU/L range while the serum oestradiol is <160 pmol/L.


The median age at menopause is around 50 years but in 10% of women it occurs below age 46. In a few women the peri-menopause starts in their thirties and can be prolonged over 3-8 years.

During HRT (hormone replacement therapy) it is not usual to monitor FSH or oestradiol. The doses of oestrogen used do not suppress FSH and would not provide contraception in a pre-menopausal woman.

Menstrual disorders see Amenorrhoea

Mercury specimen: 24-hr urine in special plastic container with HCl ref. range: acceptable <0.25 µmol/day toxic >0.5 µmol/day

Most of the public interest in mercury toxicity centres on amalgam in teeth but studies have not shown harmful effects. After an exhaustive investigation, the U.S. Public Health Service concluded there is no serious health risk. Urine mercury levels in people with filled teeth are less than 5% of the stated acceptable limit.

Organic mercury compounds have been used as fungicides with wide-spread poisoning in Iraq in 1971 when bread was accidentally made from seed wheat preserved with methyl mercury. Mercury-contaminated waste in sea-water is passed up the food chain to reach its most concentrated levels in large predatory fish such as shark, tuna and sword-fish. The Miranda Bay disaster in Japan in 1955 was due to industrial waste discharge being concentrated in edible fish.


Mercury as calomel in children's teething powders and in laxatives was found to be the cause of acrodynia (pink disease) as late as the 1940's.

Mercury poisoning causes renal damage and neurotoxicity.

ME syndrome see Chronic fatigue syndrome

Metanephrines specimen: 24-hr urine collected into HCl.

A test formerly used in suspected phaeochromocytomas.

Methadone

specimen: random urine

see Drug screen � pre-employment screen and drugs of abuse

Methaemalbumin specimen: serum


The presence of methaemalbuminaemia is diagnostic of intravascular haemolysis.

Methaemoglobin see Haemoglobin pigments

Methicillin resistant S. aureus

see MRSA (methicillin resistant Staphylococcus aureus)

Methyl bromide

Methyl bromide is used for fumigation. Agricultural officers who use these chemicals are checked annually.

Mg see Magnesium (Mg)


MGUS (monoclonal gammopathy of uncertain significance) see Immunoglobulins, IgA, IgG, IgM

Microalbumin

specimen: random urine or early morning urine or 24-hr urine or timed urine � overnight or other timed period

ref. range:

ACR - albumin- 24-hour AER - albumincreatine ratio output excretion ratemg/mmol creat. mg/day µg/min

normal <2.5 <30 <20microalbuminuria 2.5-25 30-300 20-200macroalbuminuria >25 >300 >200

Microalbumin is a test currently used only in diabetics where it is a marker for early nephropathy at a stage where it is reversible with good control of hypertension and hyperglycaemia. In Type 2 diabetes, it is a powerful risk marker for vascular disease.

The term microalbumin refers to ordinary albumin (not a tiny albumin) found in urine at concentrations below 300 mg/L, the cut-off point for conventional urine dipsticks. Concentrations above this are called macroalbuminuria or persistent proteinuria or clinical proteinuria and indicate irreversible nephropathy.


Because biological variance of urine microalbumin is high (± 50%) and because transient increases in microalbumin can be due to urinary tract infection, exercise, intercurrent illness etc, a first abnormal result should be followed by others over a 2-12 month period and include an MSU looking for UTI. The possibility of non-diabetic nephropathy also needs to be considered.

Presence of microalbuminuria above 70-100 mg/day in diabetes, particularly Type I, is usually an indication for scrupulous control of even mild degrees of hypertension using an ACE inhibitor as the agent of first choice in most patients.

Microcytosis

Microcytes are red cells with an MCV mean cell volume below 80. Causes are:

Iron deficiency The commonest cause. In severe cases the MCV can be in the 50-60 range.

Thalassaemia The MCV, which lies in the 63-80 range, is disproportionately low, relative to the degree of anaemia and is not altered by iron therapy.

Anaemias of chronic disorders The MCV is usually normal but sometimes falls in the 75-80 range.

Sideroblastic anaemias The blood film is characteristically dimorphic.

Microfilaria see Filariasis


Microglobulin

see Beta 2 microglobulin

Microhaematuria see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections): haematuria

Microsomal antibodies see Thyroid antibodies

Microsporum canis see Dermatophytes


Minimal bleeding disorders

Patients with a bleeding history but with a variable prolongation of the bleeding time are often classified as having a "minimal bleeding disorder". The isolated long bleeding time is presumed to be secondary to a platelet function defect. The same condition is sometimes referred to as a long bleeding time syndrome. Patients with suspected von Willebrand's disease can be placed in this group if they do not fulfill all the criteria for von Willebrand's but have a bleeding syndrome characterised by cutaneous bleeding.

see also von Willebrand's disease (vWD)

Mitochondrial antibodies specimen: serum

Mitochondrial antibodies are seldom found in normal people. Their main use is in the diagnosis of primary biliary cirrhosis - 90% of patients are positive. They are sometimes present in chronic active hepatitis and occasionally in other autoimmune disorders.

Mixed connective tissue disease see MCTD (mixed connective tissue disease)

Molecular genetics - genetic studies


Increasing numbers of inherited diseases are now identifiable using genetic studies. The local genetic laboratory should be consulted.

Tests are available or are being developed for:

Fragile X syndrome Myotonic dystrophy Prader Willi syndrome & Angelman syndrome Huntington disease Spinocerebellar ataxia Familial adenomatous polyposis Multiple Endocrine Neoplasia Type 2 Spinocerebellar muscular atrophy Spinal muscular atrophy Duchenne muscular dystrophy Cystic fibrosis Breast cancer testing Adrenoleukodystrophy Hereditary haemochromatosis

Monoclonal bands see Immunoglobulins, IgA, IgG, IgM

Monoclonal gammopathy of unknown significance (MGUS) see Immunoglobulins, IgA, IgG, IgM


Monocytes Causes of monocytosis include:

• subacute and chronic bacterial infections � TB, endocarditis, syphilis, rickettsial infections

• protozoan infections � malaria

• non-infectious inflammatory disorders � vasculitis, collagen disorders, non-infective granulomas such as sarcoidosis, ulcerative colitis, Crohn's disease

• chronic myelomonocytic and monocytic leukaemias

Mononucleosis see Infectious mononucleosis

Moraxella catarrhalis

Previously known as Branhamella and Neisseria catarrhalis. Once considered to be non-pathogenic but now a proven cause of upper respiratory tract infection. It is a common cause of otitis media and sinusitis in children and is frequently recovered from the sputum of patients with chronic obstructive airways disease. Most strains, >95%, produce a beta-lactamase which confers resistance to penicillin and amoxycillin. Most strains are susceptible to amoxycillin-clavulanate, erythromycin, cotrimoxazole and tetracyclines.


Morbilli see Measles (morbilli, English measles, rubeola)

Morphine see Drug screen � pre-employment screen and drugs of abuse

MPV (mean platelet volume)

specimen: blood (EDTA)

ref. range: 6.4 - 9.7 fl

The mean platelet volume is routinely measured by electronic blood counters.

Elevated MPV may be found in:

� increased platelet turnover : ITP, hypersplenism � GPH (gestational proteinuria and hypertension) A sudden rise in MPV can

indicate onset or worsening of GPH � DIC � myeloproliferative disorders � hyperthyroidism � as an artefact in stored EDTA blood


MRSA (methicillin resistant Staphylococcus aureus) see Staphylococci

MSU (mid-stream urine) see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections)

Multiple endocrine neoplasia see MEN (multiple endocrine neoplasia)

Multiple myeloma

see Immunoglobulins, IgA, IgG, IgM: malignant paraproteins

Mumps specimen: serum

interpretation:


IgM IgG

current or recent infection + +previously infected, now immune — +never infected — —

The diagnosis of mumps is usually an easy one on clinical grounds without a blood test.

Serum amylase levels rise sharply.

Muscle disease see CK - MB and other isoenzymes

Myasthenia gravis

This is an autoimmune disorder in which neuromuscular transmission is reduced to a varying extent by acetylcholine receptor autoantibodies (anti-ACLR) which are detectable in about 80% of cases.

Diagnostically the Tensilon (edrophonium) test is used, an injection of anticholinesterase which restores neuro-muscular function.

Mycobacteria see Tuberculosis (TB)


Mycobacterium avium

Mycobacterium avium complex (MAC) infection is seen predominantly, but not exclusively, in patients with HIV infection. In that group it usually presents with dramatic fever spikes, rigors, malaise, often hepatosplenomegaly, anaemia and cholestatic liver function tests.

Otherwise normal children may also present occasionally with cervical adenopathy due to MAC. It is sometimes recovered from sputum specimens sent for TB culture. Although it can cause true respiratory tract disease it is often just a coloniser in an abnormal respiratory tract. Evidence for it being a pathogen includes repeated isolation, a positive smear result and CXR changes. Treatment regimens include ethambutol and clarithromycin with or without rifabutin. Decisions on whether to treat and with what, require specialist advice.

Mycology see Dermatophytes Candida Malassezia furfur

Mycoplasma pneumoniae specimen: paired sera


Mycoplasma is a bacterium not demonstrable with usual stains or growth media. It is the commonest cause of atypical pneumonia, particularly in children and young adults, and can spread as a low-grade epidemic. It responds well to erythromycin or tetracycline but not to penicillin.

Diagnosis is by exclusion, by response to therapy, and by demonstrating a rising titre in paired sera, the first collected as soon as possible in the illness, the second 2 weeks later. Not infrequently the antibody titre has already plateaued by the time the first specimen is collected.

see also Pneumonia

Myelodysplastic syndromes (MDS)

Also known as evolving leukaemia or preleukaemia.

These conditions are primary bone marrow disorders which usually behave as slowly evolving bone marrow failure syndromes. Most often they present insidiously and in an older population. A variety of peripheral blood findings may be noted including pancytopenia, refractory anaemia, macrocytosis with anaemia, neutropenia and thrombocytopenia. Diagnosis is by excluding vitamin deficiency (B12, folate) and demonstrating dysplastic features in the bone marrow. Chromosome analysis and cell marker studies may also be performed on the bone marrow. Management is usually by supportive care but in selected patients more aggressive therapy maybe indicated.

Myelofibrosis

Myelofibrosis is a chronic myeloproliferative disorder characterised by bone marrow fibrosis, extramedullary haemopoiesis, splenomegaly and a leucoerythroblastic blood


film. The condition may present as myelofibrosis at the outset or be the endstage of another myeloproliferative disorder such as polycythaemia vera or essential thrombocytopenia. Survival varies with a median of four years. Therapy includes blood transfusions, cytoreductive therapy (usually hydroxyurea) for thrombocytosis, and splenectomy in selected cases.

see also Myeloproliferative disorders (MPD)

Myeloma see Multiple myeloma

Myeloproliferative disorders (MPD)

These conditions are characterised by excessive production of erythroid, myeloid and megakaryocytic cell lines (panmyelosis). In many situations only one cell line may predominate, e.g. platelet proliferation causing essential thrombocythaemia. In polycythaemia rubra vera (primary polycythaemia), erythroid hyperplasia is the most prominent feature with variable increases in myeloid cells (neutrophils) and platelets. There may also be excessive proliferation of reticulin and fibroblasts within the bone marrow giving rise to myelofibrosis. Acute myeloid leukaemia can develop as a terminal event, usually untreatable, in any of the MPDs.

see also Myelofibrosis

Myocardial enzymes see Myocardial markers for infarction (MI) and ischaemia


CK (creatine kinase) total Troponin I (TnI) and Troponin T (TnT)

Myocardial markers for infarction (MI) and ischaemia specimen: serum

Because a patient with the typical clinical picture of an MI is admitted forthwith to a coronary care unit, community laboratories do not often have to make the diagnosis. There are, however, a few patientes who want to stay wherethey are or have had an unreported episode of chest pain during the past week and in these tests will be required.

The markers of myocardial damage are, in decreasing order of specificity, troponins I & T, CK - MB, total CK, myoglobin, AST and LD.

AST and LD no longer have a useful role.

Myoglobin, though relatively nonspecific, is the earliest to rise and can appear within the first 6 hours.

The remaining four typically start to rise 4-12 hours after infarction, reach a peak and return to baseline over a period which differs between the four.

elevated forCK - MB 2-3 daystotal CK 2-3 daystroponin I 4-7 daystroponin T 4-10 days


Of these, the troponins are the most specific and usually, when elevated, indicate infarction. Small elevations found in unstable angina may indicate ischaemic damage and carry a poorer prognosis than a normal level. Troponins do not rise earlier than CK but their longer period of elevation is useful, e.g. when chest pain occurred several days earlier.

CK-MB is falling into disuse since the troponins arrived, though it may be useful in plotting successive reinfarctions.

An elevated total CK is non-specific but if serial CK measurements follow the typical time-course of an MI, they support the diagnosis. A small MI may occasionally be suggested by CK changes that stay within reference range but show a typical peak over 2-3 days.

Mycoplasma hominis

A cell-wall defective bacterium resident in the female genital tract in 5-10% of healthy women. It is commonly found in bacterial vaginosis. M.hominis is a cause of salpingitis as well as post-abortal or post-partum fever where it has been isolated from the blood of 10% of women. The latter two conditions appear to be self-limiting though antibiotic treatment may decrease the duration of fever. The agent of choice


is doxycycline. In contrast to Ureaplasma urealyticum and M. pneumoniae, M hominis is resistant to erythromycin.

Myoglobin specimen: 10ml random urine

Myoglobinuria occurs after skeletal muscle trauma or myocardial infarction (MI). After major trauma, myoglobin imparts a coffee colour to urine but small amounts, as in MI, are detectable only by chemical tests

see Myocardial markers for infarction (MI) and ischaemia

Mysoline (primidone) specimen: serum

Mysoline is metabolised to phenobarbitone which is responsible for much of the drug's anticonvulsant activity. Mysoline drug levels are monitored as phenobarbitone, whose therapeutic range is 60-170 µmol/L.

N


Na+ (natrium) see Sodium (Na+), serum

NAP (neutrophil alkaline phosphatase) score specimen: blood (EDTA or heparin)

ref. range: 20 - 80

Films must be made within a few hours of collecting the specimen. Although the test is of low specificity it is of some value in the following conditions:

elevated NAP polycythaemia vera (NAP up to 300) myelofibrosis infections other inflammatory conditions pregnancy reduced NAP chronic myeloid leukaemia PNH

Neutrophil alkaline phosphatase activity is present in the specific granules of all myeloid cells with highest activity in the youngest neutrophils.

Narcotic screen see Drug screen � pre-employment screen and drugs of abuse


Nasal swabs

After moistening the swab with transport medium, it is gently inserted up to 2cm into the nostril, upwards and backwards, and rotated against the midline nasal septum.

Nasal swabs are taken when looking for carriers of Staph aureus, particularly MRSA. Usually only one swab is collected per patient, inserted consecutively into each nostril.

Nasopharyngeal swab see Bordetella pertussis

National Testing Centre ee Neonatal screening

Necator americanus see Hookworm


Needlestick injuries

Needlestick refers to the risk of hepatitis B (HBV) hepatitis C (HCV) or HIV infection when a blood-contaminated needle or sharp object punctures the skin.

Investigations

Bloods from the exposed workers and the source specimen should be tested for markers of infection and immunity.

• HIV antibody • HBs antigen • HBs antibody • HCV antibody The event must be fully documented and the exposed worker counselled and kept informed.

Hepatitis B • No action is required if

worker is antibody +ve � they are already immune source is antigen �ve � the blood is not infective for HBV worker is antigen +ve � they are already infected from some other

source, follow-up is as for any HBs ag positive patient.

• Action is required if worker is antibody -ve and antigen -ve AND source is

antigen +ve or not known

� 400 IU of hepatitis B immune globulin within 3 days, preferably within 2 days

� start course of HBV vaccine


Hepatitis C

• no prophylaxis is available • if the source is HCV -ve � no risk for HCV • if source is +ve and worker -ve, the worker is at risk. Do follow-up tests at 3

and 6 months. If they seroconvert, refer for specialist follow-up. • if worker is HCV +ve, they are already infected.

Refer for specialist follow-up. HIV

• if source is HIV -ve � no risk for HIV • if worker is HIV +ve � they are already infected • if source is HIV +ve, refer immediately to an HIV specialist. PEP (post-

exposure prophylaxis) should ideally commence within 2 hours of exposure. PEP reduces risk of infection by 80%. The agents in use in 2000 are zidovudine, lamivudine and indinavir.

• if the source is unknown, e.g. a needle in a bag of discarded needles, the risk should be estimated and discussed with the worker. If both agree risk is negligible, no further action is required.

• If the risk is believed to be significant, immediately contact an HIV specialist

for a further opinion on whether PEP should be commenced.

What is the risk?

Of the three viruses, HBV is the most infective (30%) followed by HCV (3%), then HIV (0.3%).

This means, for example, that if no PEP is used in a known HIV +ve needlestick, the risk to the worker is 0.3%.


Prevention

All health care workers should be immunised against HBV.

Venepuncturists and nurses giving injections should be trained in safe practice.

Needles and other blood-contaminated sharps must be disposed of into puncture-proof containers.

Neisseria

These gram-negative diplococci are typically found inside neutrophils in direct smears from lesions. The two main pathogens are N. gonorrhoeae and N. meningitidis. N. catarrhalis, a member of the normal flora of the throat, was known as Branhamella catarrhalis and is now known as Moraxella catarrhalis (qv). It is a recognised respiratory tract pathogen.

A. Neisseria gonorrhoeae

specimens: swabs must be placed in transport medium immediately after collection. Store at room temperature, not in the fridge, and transport to the laboratory as soon as possible � they will survive 24-hours in transport medium. In general, Neisseria are sensitive to drying, sunlight, heat, cold and many disinfectants.

The main infections are:

Male STD Urethritis and sometimes epididymitis. The organism can also sometimes be recovered from the rectum and throat.


Female STD Endocervicitis is the initial infection with variable spread upwards to fallopian tubes and downwards to urethra and perianal skin. As with males, gonococci also grow in the throat and rectum. Neonatal conjunctivitis Acquired during birth from an infected mother.

Gonococcal arthritis A suppurative arthritis. Synovial fluid aspirate establishes the diagnosis. Treatment Until recently 96% of gonococci in New Zealand have been susceptible to penicillin but in 1991 there was a sudden increase in penicillin-resistant strains. Penicillin resistance resistance now runs at approximately 15%. The most commonly used treatment for uncomplicated gonorrhoea is ciprofloxacin 500 mg as a single dose. Less than 2% of New Zealand isolates are resistant to ciprofloxacin and at the time of writing all resistant strains have been acquired outside the country. Ceftriaxone 125 mg intramuscularly as a single dose is an alternative treatment. As with any STD, treatment of partners is essential. Concomitant infection with Chlamydia is common and empirical treatment for this is recommended, e.g. 1g azithromycin stat.

B. Neisseria meningitidis

The causative organism of meningococcal meningitis and septicaemia which can occur sporadically or in epidemics. Travellers to countries where epidemics occur, e.g. Nepal, should be vaccinated according to recommendations current at the time of travel. There are three main sub-groups, A, B and C. Most infections in New Zealand are group B for which there is currently no commercially available vaccine.

Suspected meningococcal meningitis is a medical emergency and in the community situation, parenteral antibiotics, e.g. IM amoxycillin or penicillin, should be given by the diagnosing doctor before sending the patient to hospital.


Neonatal group tests on cord blood

specimen (cord blood): · blood (EDTA)· serum

tests: · blood count· blood group· direct Coombs· bilirubin

These tests are usually done only when the infant is at risk for haemolytic disease (qv), not as a routine.

Neonatal jaundice see Jaundice

Neonatal reference ranges

The drama of transition from an intrauterine to independent existence is reflected in laboratory values which change rapidly during the first week of life and to a lesser extent in the weeks that follow. Where an unexpected result is obtained, it should be checked against the appropriate neonatal reference range. An extreme example is TSH which surges from a mean level of 9 units at birth to an average peak of 85 half an hour later before falling back to near adult levels at 5 days.

Neonatal screening


specimen: dried blood spots on "Guthrie" card �allow to dry before placing in plastic bag.

Tests are performed at the National Testing Laboratory, National Women's Hospital, phone (09) 6310 705. All infants born in New Zealand, about 60,000/year, are tested for the following:

Condition Test Incidencecystic fibrosis trypsin 1 : 3,000hypothyroidism TSH 1 : 5,000phenylketonuria phenyl alanine 1 : 15,000galactosaemia galactose 1 : 50,000biotinidase deficiency biotinidase 1 : 60,000congenital adrenal hyperplasia 17-OH progesterone 1 : 225,000maple syrup urine disease leucine 1 : 250,000

The infant must have been feeding on milk for at least 2 days before specimen collection, the usual age being 5 days. Cards collected up to the age of 1 month give valid results or up to 2 months for cystic fibrosis.

Blood spot cards can be tested by the lab up to 1 month after collection. The NTL completes the tests within 1 week of arrival at the lab. At present they notify positive results only.

A single screening test giving an apparently normal result can never exclude the above conditions. If a neonate or infant is unwell or not developing normally, appropriate tests should be repeated or added.

Netilmicin see Aminoglycoside, serum levels


Neuroblastoma see Catecholamines

Neutrophil alkaline phosphatase see NAP (neutrophil alkaline phosphatase) score

Neutrophils (polymorphs)

Neutrophil counts are expressed and interpreted in terms of the absolute count rather than % of total white cell count.

A. Neutropenia

The usual adult reference range is 2.2 - 7.5 x 109/L.

Mild neutropenia, 1.5 - 2.2 x 109/L is a common finding, often suspected to be caused by an immune mediated mechanism (immune neutropenia) when drugs are not implicated.

Below 0.5 x 109/L there is an increase in spontaneous infection with a dramatically increased risk below 0.2 x 109/L (= agranulocytosis).

Common causes of neutropenia:

- viral infection, sometimes with an associated thrombocytopenia - some bacterial infections, e.g. typhoid


- overwhelming sepsis, often with toxic granulation of neutrophils and a shift to the left.

- B12 or folate deficiency - aplastic anaemias - malignancy � haematological malignancy or metastatic deposits in bone

marrow. - immune-mediated � post viral, Felty's syndrome, SLE - hypertension - thyrotoxicosis - chronic benign neutropenia, including cyclical neutropenia � drugs those more commonly implicated are:

� phenylbutazone, indomethacin � chlorpromazine, promazine, other phenothiazines � carbamazepine � propylthiouracil, carbimazole � sulphonamides, cotrimoxazole � dapsone � thiazides � captopril

Cyclical neutropenia

Characterised by periodic fluctuations in the neutrophil count with the nadir occurring usuallyat three weekly intervals. In the most severe cases the neutropenia may be extremely low, < 0.1x10.9/L , with infective complications, malaise and fever. Hospital admission may be required as occasionally these may be life-threatening events. In some patients, due to the severity of the neutropenic episodes and the infective complications, growth factor support with granulocyte colony stimulating factor (G-CSF) is required. B. Neutrophilia

A neutrophil count >7.5 x 109/L.

Minor degrees of neutrophilia are a common response to almost any disease process. In more serious disorders, neutrophil precursors may be present, the sequence from


cell division to maturity being myeloblast, myelocyte, meta-myelocyte, band neutrophil, segmented neutrophil. An increase in band neutrophils, meta-myelocytes and eventually myelocytes, i.e. a "shift to the left", should prompt a search for serious disease.

Causes of neutrophilia

- Bacterial infection � there may be a shift to the left and with more severe

infections there may be toxic granulation and eventually neutropenia as the marrow is overwhelmed.

At the other end of the scale is the leukaemoid reaction, a massive outpouring of cells in response to infection with counts up to 80 x 109/L and a striking shift to the left.

- Tissue injury � due to infarction, burns, surgery, trauma and other processes causing necrosis.

- Other inflammatory disorders � connective tissue disorders, etc. - Malignancy - Drugs � steroids, epinephrine, heparin - Other � haemorrhage, stress, metabolic disorder

Non-gonococcal urethritis (NGU)

Chlamydia is the main pathogen but Trichomonas vaginalis can also cause symptoms. In about half of NGU's an organism is not isolated.

Treatment is doxycycline, 100mg 12-hourly for 7-10 days.

see also Chlamydia trachomatis


Non-thyroidal illness see Thyroid disease � diagnosis and monitoring, paragraph D

Noradrenaline see Catecholamines

Normal range see Reference ranges and the concept of normality

Nose see Nasal swabs

Nosocomial infection

An infection acquired in hospital, e.g. some MRSA or pseudomonas infections.


NSAIDs and renal toxicity.

NSAIDs can cause acute renal insufficiency, usually reversible, due to inhibition of vasodilatory prostaglandins.

Susceptible patients are the elderly and those with pre-existing renal disease, cardiovascular disease, an oedematous state or concomitant use of diuretics or aspirin. These should be monitored 1-3 weeks after commencing NSAIDs and then 3-monthly for long-term use, looking for:

� rising s. creatinine

� hyperkalaemia

� proteinuria

N-telopeptide

specimen: second morning spot urineDo not add preservative.

ref. range: female 14-74 BCE/mmol creatininemale 3-51 BCE/mmol creatinine (BCE = bone collagen equivalent)

Excretion of N-telopeptide varies through the day being highest at night. In an attempt to improve standardisation, a second morning urine collect (urine formed after rising) is usual. A change of 50% is needed to show benefit of treatment.

The female range is for pre-menopausal women. After the menopause, developing osteoporosis can double N-telopeptide levels.

N-telopeptide is a marker for bone turnover in conditions such as Paget's disease where there is increased bone resorption. Reduction of N-telopeptide is a measure of therapeutic effect of biphosphonates or other medication.


see also Bone turnover markers


O

Occult blood see Faeces for occult blood

Oestradiol (E2) specimen: serum

ref. range:

pmol/L

adult female during cycles — see diagram under FSHearly follicular <300ovulatory surge 500-2000luteal phase 150-1400post-menopausal <160adult male <160

� oral contraceptives are associated with very low levels

� pregnancy is associated with very high levels


The assay is specific for oestradiol. Other oestrogens such as ethinyl oestradiol or conjugated equine oestrogens (premarin) are not detected.

Oestradiol is the major endogenous oestrogen in ovulating women. It rises to a pre-ovulatory peak mid-cycle, falls and then returns to a luteal phase plateau before falling again prior to menstruation. Indications for estimating oestradiol are strictly limited:

� during artificial induction of ovulation

� investigation of feminising states including precocious puberty, gynaecomastia

� investigation of possible pituitary-gonadal deficiency states in women.

It is not used during the early investigation of infertility, for diagnosing menopause, for monitoring HRT (hormone replacement therapy), or for investigating irregular menstruation.

see also FSH (follicle stimulating hormone) and LH (luteinising hormone)/LH

Oestriol (E3)

Serum or urine oestriols were once used for 3rd trimester foeto-placental monitoring. They have not been replaced routinely by any other biochemical test.

Unconjugated serum oestriol is used when testing for Down's syndrome during the first or second trimester.



Oestrogen receptors in breast tissue see Breast tumour hormone receptors

Oestrogens - Oestradiol (E2) (qv), is the major endogenous oestrogen during child-bearing

years - Oestriol (E3), is the most abundant oestrogen during pregnancy - Oestrone (E1), is the major circulating oestrogen after the menopause

Oestrogens are now measured in serum, not urine.

OH see 17-hydroxy progesterone (17-OHP)

OGTT see GTT (O = oral)

Onychocola canadensis


This is an uncommon cause of onychomycosis (qv), usually occurring in elderly women and frequently involving all nails. There are reports of it causing skin infection.

Treatment: itraconazole or terbinafine.

Oral contraceptives

These can affect a wide range of laboratory tests:

clotting factors increase FSH suppressed glucose tolerance may decrease a little haematinics B12 and folate decrease, transferrin & IBC increase immunological tests false +ve ANA and rheumatoid factor LH suppressed lipids triglyceride and HDL increase, LDL cholesterol can

show minor decrease liver functions bilirubin, AST, ALT, GGT,ALP can all increase oestradiol suppressed progesterone suppressed prolactin can be elevated up to 2x proteins carrier globulins for cortisol, T4, iron and copper all

increase; albumin and bound calcium decrease; alpha-1 antitrypsin and alpha-2 macroglobulin increase


Organophosphate toxicity see Cholinesterase

Osmolality

specimen: serum plain tube urine early morning, or random, or timed collect, or 24-hr urine.

Preservative is not required. ref. ranges: serum 280-300 mosmol/kg water

urine 50-1200 mosmol/kg water

Urine osmolality, which is under the control of pituitary ADH, varies over a wide range to ensure that alterations in fluid intake have little effect on the tightly controlled serum osmolality. Urine osmolality is typically highest on rising in the morning because of the absence of fluid intake during sleep. An osmolality >600 (especially >800) makes diabetes insipidus unlikely.

An approximate serum osmolality is given by the formula:

osmolality = 2 x Na + + urea + glucose The normal physiological response to hyponatraemia is the secretion of a dilute urine with osmolality <100. A higher osmolality suggests SIADH.

Osmotic fragility of red cells specimen: blood (heparin)

ref. ranges:


fresh blood incubated blood

initial haemolysis 0.50-0.45 0.70-0.55complete haemolysis 0.40-0.20 0.40-0.20

This is a test for spherocytes which are more sensitive to lysis in hypotonic saline solutions than are normal red cells. The figures refer to strength of saline solutions at which initial and complete haemolysis occur, 0.9% being isotonic. Sensitivity is increased by pre-incubation of red cells for 24 hours at 37°C.

The test is useful in the diagnosis of hereditary spherocytosis.

Osteoporosis/Osteomalacia

Osteoporosis, a reduction in the quantity of normally mineralised bone, is seen mainly in post-menopausal women who in old age can have problems with fractures, particularly of neck of femur, wrists and vertebral bodies.

In osteomalacia, bone shows defective mineralisation. Vitamin D deficiency in childhood (rarely) or old age are the usual causes along with renal osteodystrophy in chronic kidney disease.

In old age, osteoporosis and Vitamin D deficiency can act together to accelerate loss of bone density.

Laboratory tests in the common metabolic bone diseases are:

S. calcium S. phosphate S. ALPosteoporosis N N Nosteomalacia ↓ or N ↓ ↑Paget's disease N N ↑ ↑ ↑renal osteodystrophy ↓ or N ↑ ↑1° hyperparathyroidism ↑ N or ↓ N or ↑tumour metastases N or ↑ ↓ N or ↑ ↑


Because multiple myeloma can cause generalised oseteoporosis as well as discrete lytic lesions, protein EPP should be performed.

Bone turnover markers (qv) give a measure of disease activity.

Osteoporosis/osteomalacia and their associated fracture risks in post-menopausal women, can be actively prevented using physical activity, HRT, calcium and vitamin D supplements, and biphosphonates.

Otitis see Ear swabs & infections

Ova in faeces see Faeces for ova and parasites

Ovarian function see FSH (follicle stimulating hormone) and LH (luteinising hormone) for ovarian failure and menopause

Progesterone for detection of ovulation

Oestradiol (E2) for oestrogenic activity

Polycystic ovary syndrome (PCOS)


Overdose screen see Drug screen � overdose

Ovulation see Progesterone

Oxalate

specimen: 24hr-urine collection with HCl preservative

ref. ranges : female 0.04-0.31 mmol/24hrmale 0.10-0.41 mmol/24hr

Hyperoxaluria, with or without formation of oxalate stones, can be due to fat malabsorption, dietary oxalate excess, Vitamin C overdose, hereditary hyperoxaluria (rare) or industrial toxicity.

About 10% of urine oxalate normally comes from the diet but this fraction increases with excessive intake of oxalate rich foods including spinach, rhubarb, strawberries, tomatoes, prunes and tea.

P


P4 see Progesterone

Paget’s disease of bone

Asymptomatic Paget�s is a common cause of elevated ALP (150-500 units or higher) in the elderly and the ALP level is an indication of disease activity and response to treatment. 24-hour urine N-telopeptide is another indicator used in monitoring treatment.

A bone scan is a sensitive method for identifying foci of Paget's disease.

see also Alkaline phosphatase (ALP)

Pancreatitis see Amylase, serum

Pancytopenia A reduction in all three cellular elements in blood i.e. anaemia, leucopenia (neutropenia) and thrombocytopenia. An unexplained pancytopenia is always an indication for a bone marrow biopsy.

Causes include:

• haematological disorders requiring bone marrow examination � aplastic anaemia, leukaemias, myeloma, myelodysplastic disorders, metastatic tumour


• drug effects • B12 or folate deficiency • hypersplenism • SLE, PNH • overwhelming infection, HIV

see Neutrophils (polymorphs),


Thrombocytopenia, and individual disorders for more detail.

PAP see Cervical cytology (PAP smear) Acid phosphatase, prostatic (PAP) (prostatic acid phosphatase)

Paracetamol (acetaminophen) specimen: serum, for quantitative measurement and assessment of risk urine, a qualitative test where ingestion is suspected but not known

About 4 hours after an overdose of paracetamol, the serum level reaches its peak and then declines. Charting the serum level against time elapsed since ingestion gives a measure of risk of liver toxicity and determines whether antidote should be given. At 4 hours, a paracetamol level above about 1mmol/L is an indication for giving N-acetylcysteine.

Paraprotein see Immunoglobulins, IgA, IgG, IgM

Paraquat

specimen: • random urine for screen test• plasma (heparin), for quantitation - must be centrifuged immediately

Horticultural workers are not monitored on a routine basis.


After suicidal ingestion of large amounts of paraquat, the plasma level in relation to time of ingestion will give an estimate whether the outcome is likely to be fatal.

Paraquat will be undetectable within a week of even a large intentional overdose.

Parasites in faeces see Faeces for ova and parasites

Parathyroid hormone (PTH)

specimen: plasma (EDTA)

ref. range: 1-5 pmol/L

Elevations of PTH with elevated calcium:-

• primary hyperparathyroidism due to solitary adenoma (85%) or hyperplasia (15%) is the commonest cause. Management of lesser degrees of abnormality is usually conservative, surgery being required only when the hypercalcaemia is causing symptoms or tissue damage.

see also Calcium (total)

MEN • lithium therapy


• familial benign hypocalciuric hypercalcaemia is a rare autosomal dominant disorder in which excessive renal calcium reabsorption is associated with relatively small elevations in PTH. Parathyroid surgery is contraindicated.

Elevations of PTH with normal or low calcium

• renal failure � 2° hyperparathyroidism • vitamin D deficiency

Parietal cell antibodies specimen: serum

About 90% of patients with pernicious anaemia have parietal cell antibodies. These can be found in other organ-specific autoimmune disorders such as thyroiditis and in 10-15% of apparently healthy elderly people.

see also Pernicious anaemia

Paroxysmal nocturnal haemoglobinuria (PNH) PNH is a rare, acquired haematological disorder usually presenting in adult life.

Its features include:

• intravascular haemolysis • venous thrombosis • marrow hypoplasia

PNH is due to an acquired mutation giving rise to a clone of abnormal stem cells affecting erythrocytes, leucocytes and platelets.


The haemolysis, though chronic, is intermittent, occasionally paroxysmal with severe anaemia. It is mediated by complement and is made worse by reduction in blood pH as occurs at night, during exercise, or in vitro as in Ham's test which is used in diagnosis.

The non-specific laboratory abnormalities include:

• anaemia, neutropenia, thrombocytopenia • reduced haptoglobins, reticulocytosis • haemoglobinuria, haemosiderinuria

More specific tests for PNH are:

• absence of CD59 (qv) activity on the erythrocyte cell surface • Ham's (qv) acidified serum lysis test • sucrose lysis test

Pasteurella multocida A gram-negative bacillus that is isolated from skin lesions. The organism is a common inhabitant in the mouths of cats and dogs and infection is frequently associated with animal bites or scratches. Regional lymphadenopathy, chills and fever can result. It is susceptible to penicillin and amoxycillin. Wound debridement may also be necessary.

Paternity testing specimen: whole blood (EDTA) from:

- baby (requires mother's permission) - father - mother � not essential but desirable


Blood is preferably stored at 4ºC but room temperature for a day or two is acceptable. The method involves DNA identification using white cells as the source of nuclear material. Where the result has legal implications, a recognised collection protocol must be observed.

Paul Bunnell test for heterophile antibodies seeInfectious mononucleosis

PBG (porphobilinogen) see Porphyrias

pCO2 see Blood gases & pH

PCOS see Polycystic ovary syndrome (PCOS)

PCR Polymerase chain reaction


A molecular method to amplify genetic material. The amplified sequence can then be detected by a variety of methods. Often used to detect small numbers of organisms in a specimen, e.g. Toxoplasma gondii in amniotic fluid or M. tuberculosis in CSF. PCR is also used to amplify sequences for human gene studies, e.g. paternity testing and some inherited genetic disorders.

PCT (prothrombin clotting time) see PR (prothrombin ratio) INR (international normalised ratio)

PCV (packed cell volume) see Blood count

Penicillin allergy

When a patient says they are allergic to penicillin, the diagnosis can be confirmed by skin tests conducted in a specialist setting and desensitisation achieved if penicillin therapy is regarded as essential.

It is more usual to accept the patient's diagnosis and avoid penicillin, particularly injections which cause more severe reactions than oral forms.

Penicillin allergic status can change over time, from positive to negative and back again and for this reason even a negative skin test in a person who claims sensitivity, cannot be relied on to stay negative.


Approximately 10% of penicillin-allergic patients will be allergic to cephalosporins also. It is prudent to avoid cephalosporins in patients with immediate-type reactions to penicillin and vice versa.

Percentage hypochromia

ref. range: <3%

The percentage of hypochromic red cells is a useful guide to iron status in patients with chronic renal failure who are being treated with recombinant erythropoietin (EPO).

Peripheral neuropathy

Pathologies to consider include:

� diabetes � viral infection: Guillain-Barré

� alcoholism

� connective tissue disorders

� paraproteinaemias

� toxins: lead

� drugs: amiodarone, phenytoin, nitrofurantoin and others


Pernicious anaemia An autoimmune disease, rare before the age of 40, causing destruction of gastric parietal cells and intrinsic factor and hence reduced absorption of Vitamin B12. Laboratory features include some or all of the following:

• anaemia, thrombocytopenia, neutropenia • serum vitamin B12 reduced • blood film features � oval (not round) macrocytes

� hypersegmented neutrophils • macrocytosis � MCV up to 120 • intrinsic factor and/or parietal cell antibodies � 90% are positive for one or both of

these • folate � serum levels normal or increased

� red cell levels normal or reduced • bone marrow � megaloblastic change • prominent increase in reticulocytes 10 days after commencing therapy with B12 • Schilling's test positive � not an essential test if other typical features are present

Pertussis see Bordetella pertussis

pH, blood see Blood gases & pH

pH, urine A non-contributory test except in renal tubular acidosis where a useful screen is to collect a first morning urine in a filled, well-sealed container which should be delivered to the laboratory without delay. A urine pH below 6.0 makes renal tubular acidosis very unlikely.


Normal urine is acid but, on standing, contaminating organisms convert urea to ammonia and the urine turns alkaline, a process which accelerates haemolysis of red cells if present.

Phaeochromocytoma see Catecholamines

Phenobarbitone specimen: serum

therapeutic range: 65-170 µmol/L trough level

The half-life of phenobarbitone is 4 days.

see also Anticonvulsants

Phenylalanine specimen: blood spots on Guthrie card

screening for PKU � see Neonatal screening

monitoring PKU � quantitative phenylalanine levels are also done on blood spot specimens

Phenylketonuria (PKU) see Phenylalanine


Phenytoin see Dilantin (phenytoin)

Phosphatases see Acid phosphatase, prostatic (PAP)

Alkaline phosphatase (ALP)

Phosphate specimen: serum

ref. range:

Age (yrs) mmol/L0-1 1.4-2.42-10 1.0-2.0>10 0.7-1.5

Phosphate, also called inorganic phosphorus, is used diagnostically in two main situations.

• hypercalcaemia � levels are reduced or low normal in primary hyperparathyroidism and vitamin D deficiency, but are usually increased or normal in other hypercalcaemias.

• renal failure � phosphate is elevated.

A wide range of other disorders cause hyper- or hypo phosphataemia but diagnostic value is limited.


Phosphate levels can be falsely raised if the specimen is haemolysed.

Phospholipid antibodies see Anticardiolipin Lupus anticoagulant (LAC) Antiphospholipid antibody syndrome (APS)

Pinworm see Enterobius vermicularis (pinworm) vermicularis

Pituitary hormones see Hypopituitarism

PKU (phenylketonuria) see Phenylalanine

Plain tubes for blood collects see Tubes for blood collects

Plasma renin activity


see Aldosterone and renin, plasma

Plasma volume see Blood volume

Platelet aggregation

Performed in selected patients presenting with platelet function defects suspected on the basis of a prolonged bleeding time or a clinical history not otherwise explained. Platelet function abnormalities such as release type defects or Glanzmann's thrombasthenia are diagnosed in this way.

Platelet antibodies specimen: serum

blood (EDTA)

Platelet antibody tests are most often performed in the investigation of an isolated thrombocytopenia. Both platelet-associated (PAA) and serum platelet (SPA) antibodies are measured. A positive result for either test supports an immune aetiology though immune thrombocytopenia may be present in patients with negative PAA and SPA.

Platelet count specimen: whole blood (EDTA)

ref. range:


Age (yrs) x 109/L0-12 150->12 150->12 150-

reduced platelets � see Thrombocytopenia

raised platelets � see Thrombocytosis

mean platelet volume � see MPV (mean platelet volume)

Platelet dysfunction

This is suspected in patients presenting with a bleeding history and a normal platelet count, normal coagulation factor screen but prolonged bleeding time. The term �minimal bleeding disorder� (qv) is sometimes used. Occasionally, platelet aggregation and other studies are used where further investigation is required.

Platelet function disorders can be:

congenital rare defects of aggregation, adhesion or the platelet release reaction acquired drug effects (especially ASA; NSAIDs) haematological malignancies (especially MDS) myeloma, macroglobinaemia or other paraproteinaemia uraemia immune thrombocytopenia (ITP) myeloproliferative disorders


Plesiomonas A gram-negative bacillus related to Aeromonas (qv) and occasionally isolated from patients with diarrhoea. Although there are no data on the benefits of treating Plesiomonas-associated diarrhoea there may be benefits for those with severe disease. Options include cotrimoxazole or norfloxacin for 3 days.

Pleural fluid see Aspirated fluids, synovial, pleural, ascitic etc

Pneumococcus see Streptococci Pneumonia

Pneumocystis carinii

Pneumocystis carinii was considered to be a protozoan parasite but genetic studies suggest it is most likely related to the fungi.

It causes an acute to sub-acute, often fatal, pulmonary disease in the immunocompromised. It is a major disease problem in those infected with HIV.

Diagnosis is by detecting organisms in bronchial brushings, open lung biopsy and lung aspirates. A variety of stains may be used to show the organism.


Treatment is high dose cotrimoxazole and should be discussed with those who have experience in treating this condition.

Pneumonia At the time of clinical diagnosis an attempt, often unsuccessful, should be made to obtain a sputum sample. Culture may show Strep. pneumoniae in classical lobar pneumonia; or Haemophilus influenzae and/or S. pneumoniae in pneumonia associated with chronic bronchitis.

Antibiotic therapy is usually started immediately on an empirical basis. A sputum specimen obtained after antibiotic treatment has started, will not be useful.

% susceptibleamox tetra cotr amox-clav eryth pen

H. influenzae 81 99 91 100 0¹ —S. pneumoniae —² 71 67 —² 76 68

1. The newer macrolides roxithromycin and to a greater extent clarithromycin have activity against H. influenzae.2. While pneumococci with reduced susceptibility to penicillin are also less susceptible to other B-lactam agents they usually respond to amoxycillin treatment for lung infections. Recent New Zealand data indicates that approximately 93% of pneumococci are susceptible to amoxycillin.

Atypical pneumonias These are almost as common as the classical bacterial pneumonias.

• Mycoplasma pneumoniae (qv) is the commonest particularly in children and young adults.

• Psittacosis (qv) affects those who have occupational contacts with birds, including poultry.

• Legionnaire�s disease � see Legionella • Chlamydia pneumoniae causes approximately 3% of community acquired

pneumonia in New Zealand.


• Viruses, e.g. influenza A, adenovirus, respiratory syncytial virus, cause approximately 10% of community-acquired pneumonia in New Zealand.

Treatment: With the exception of viruses, the agents causing atypical pneumonia are susceptible to erythromycin, though doxycycline is the preferred treatment for psittacosis.

PNH see Paroxysmal nocturnal haemoglobinuria (PNH)

Polychromasia Bluish staining of some red cells in a blood film suggesting an increase in reticulocytes (qv).

Polycose screen test for gestational diabetes (GDM) see Gestational diabetes mellitus (GDM)

Polycystic ovary syndrome (PCOS) This common endocrine disorder is characterised variably by:

• amenorrhoea or oligomenorrhoea • infertility / anovulation with oestrogen present • hirsutism, acne, alopecia


• mildly elevated testosterone � produced by the ovaries • increased extra-ovarian production of oestrogen • LH elevated, FSH depressed, LH/FSH ratio >2 • prolactin elevated • obesity • ovaries enlarged with multiple cysts visible on ultrasound • insulin elevated due to insulin resistance • family history of PCOS

Not all these features are necessarily present. The combination of androgen excess and obesity leads to increased extra-ovarian oestrogen production which increases LH and decreases FSH.

Treatment includes weight loss, exercise, oral contraceptives, anti-oestrogens such as clomiphene, and local treatments, e.g. electrolysis, for hirsutism. Anti-oestrogens enhance FSH secretion and may restore normal ovulatory cycles.

see also Hirsutism/virilism

Polycythaemia Is defined as a haemoglobin concentration above the reference range for age and sex.

The approach to diagnosis is to distinguish between polycythaemias due to an increased red cell mass (primary and secondary polycythaemias) and those due to a reduced plasma volume (relative polycythaemias).

A. Polycythaemia rubra vera (primary erythrocytosis) A myeloproliferative disorder usually occurring in middle or older age in which red cells, and often white cells and platelets, are increased.

Laboratory features


• Red cells � Hb and PCV are increased

The red cell mass is elevated (usually >36mls/kg in males) but the plasma volume is normal. By convention the packed cell volume is used to monitor the treatment response.

• White cells � there is an increase in neutrophils often with a shift to the left

with band neutrophils, metamyelocytes and occasionally myelocytes. • Platelets � 400 - 800 x 109/L in most cases with counts over 1000 x 109/L

occasionally. Giant forms may be present.

• NAP score � increased in 70%. B. Secondary polycythaemia Increase in the red cell mass due to tissue hypoxia caused by:

• chronic respiratory disease • congenital heart disease • high altitude

Secondary polycythaemia also occurs in some renal disorders, particularly tumours, where there is increased erythropoietin production.

C. Relative or “stress” polycythaemia The commonest form of polycythaemia, the elevated haemoglobin being secondary to a depletion in the plasma volume. By definition the red cell mass (volume) is normal. Clinical associations are:

• smoking • alcohol • stress • dehydration • diuretics


This condition is diagnosed by demonstrating a normal red cell mass and a reduced plasma volume.

Polydipsia/polyuria

Urinary frequency due to UTI (urinary tract infection) or lower urinary tract problems, can be distinguished from polyuria by collecting a 24-hr specimen to document urine volume. Causes of polyuria include:

• diabetes mellitus (random glucose levels usually above 15 when polydipsia/polyuria are present).

• hypercalcaemia • hypokalaemia • lithium therapy • psychogenic polydipsia (compulsive water drinking) � not uncommon • diabetes insipidus

To differentiate between the latter two, see


Diabetes insipidus.

Polymerase chain reaction see PCR

Polymorphonuclear leucocytes (polymorphs) see Neutrophils (polymorphs)

Polymyalgia rheumatica

A relatively common disorder, particularly in the elderly, characterised by distressing shoulder and pelvic girdle pain originating from muscles rather than joints. It is often associated with temporal arteritis.

ESR and CRP are almost invariably (but not always) raised.

Response to steroids is dramatic.

Porphyrias specimens: all must be protected from light and delivered to the lab as soon as possible.


urine: � during an attack of suspected acute porphyria, collect a random urine for PBG and deliver to the laboratory immediately.

� 24-hour urine, in dark bottle with sodium carbonate as

preservative.

faeces : casual specimen delivered to the laboratory within 5 hours. red cells : heparin tube

ref. ranges :

urine red cells faeces(µmol/day) (nmol/L) (µmol/kg)

porphobilinogen <8.8 - -uroporphyrin <36 - -coproporphyrin <300 <38 <30protoporphyrin - <925 <135

There are two main syndromes:

• Acute porphyria

� abdominal pain (autonomic neuropathy)

� peripheral neuropathy

� neuropsychiatric manifestations

Attacks are provoked by drugs that induce liver enzymes � barbiturates, alcohol, oestrogens, sulphonamides, anticonvulsants, and others. In women, neuropathic symptoms may be cyclical, associated with oestrogen peaks.

• Cutaneous porphyria


Presents with photosensitivity and blistering in sun-exposed areas, notably backs of hands, forearms, face, where accumulated porphyrins react with light to produce skin damage.

Symptoms are provoked and exacerbated by oestrogen, alcohol, and iron supplements.

Investigations During a suspected acute attack, e.g. recurrent acute abdominal pain not otherwise explained, a fresh urine sample should be taken to the lab urgently for PBG.

During latent phases of acute porphyrias, abnormalities may be undetectable.

Cutaneous photosensitivity is most often due to PCT (porphyria cutanea tarda) which is diagnosed by increases in urine and faecal porphyrins. Diagnosis of the rare erythropoietic porphyrias requires a blood specimen.

The table below lists the names of the main porphyrias in their order of frequency � PCT is the commonest, then variegate porphyria and so on.

The second column indicates whether that porphyria is cutaneous or acute or both. The test columns show the tests that should be ordered in the acute and latent phases of each porphyria.


Named porphyria Syndromes Testsurine faeces red cells

uro-& copro-&acute/ copro- proto- proto-

cutaneous neuropathic PBG porph. porph. porph.

porphyria cutanea tarda (PCT) + — — + + —variegate porphyria- acute + + + + + —- latent — — + —hereditary coproporphyria- acute + + + + + —- latent +/— — +/— —acute intermittent porphyria- acute — + + + — —- latent — + — —erythropoietic protoporphyria + — — — + +(rare)congenital erythropoietic + — — + + + porphyria (v. rare)

Post-splenectomy blood film see Hyposplenism

Potassium (K+), serum specimen: serum

ref. range: 3.5-5.0 mmol/L

A. Elevated potassiums – hyperkalaemia

Elevated potassiums are one of the most vexing problems faced by a laboratory because of the difficulty knowing whether a level of 7.5 mmol/L, for example, is harmless artefact or imminently lethal hyperkalaemia.


It is not uncommon to find unexplained elevations of K+ in healthy people in the range 5.0 - 6.0 mmol/L and, for lack of better explanation, these are usually attributed to artefact.

• Artefactual elevation

These are comon due to leakage of potassium from red cells into serum or plasma. Causes are:

� prolonged application of tourniquet with repeated hand-clenching. In cachectic patients, the elevation of serum potassium can be accentuated.

� slow, difficult blood collect causing damage (haemolysis) to red cells.

� long delay (>5 hours) between collecting and centrifuging the specimen.

� putting the specimen in the fridge; this inhibits the red cell ion pump that maintains the normal K+ gradient.

� individual patient variation in the extent of potassium leakage.

If you suspect artefactual elevations:-

• iscard elevated potassium results when the specimen has been stored more than 5 hours.

• never put electrolyte specimens in the fridge. • have the repeatd specimen collected by a skilled venepuncturist before

the morning courier collect and label it "Immediate" so that it will be analysed soon after arrival at the lab.

• Physiological elevations

� exercise can cause elevations of up to 1.0-1.5 mmol, falling over 6-8

hours.


� pregnancy serum K+ rises from a mean of 4.3 in the 1st trimester to 5.9 in the 2nd and 3rd trimesters.

� posture 0.5 mmol lower in supine compared with standing position. � time of day levels are slightly higher in early morning and fall after

meals.

• Drugs are a common cause of hyperkalaemia, particularly in the elderly

� diuretics: amiloride, triamterene, spironolactone � potassium supplements � NSAIDs � ACE inhibitors � beta blockers � digoxin in toxic doses � lithium � cytotoxics � antibiotics: trimethoprim, cephaloridine, methicillin, some penicillins,

tetracyclines, isoniazid � heparin � dietary salt substitutes which use potassium, rather than sodium,

chloride

• Pathological states

� renal failure � adrenocortical insufficiency � metabolic acidoses � very high platelet or white cell counts

What levels of hyperkalaemia are dangerous?

- Levels between 5.0 and 6.0 will seldom be a danger. Between 6.0 and 7.0 risk is increasing, particularly when the hyperkalaemia is of acute onset, as when starting


one of the drugs listed above. Patients on dialysis become acclimatised to their hyperkalaemia and can usually tolerate levels up to 7.0 or even 7.5. - B. Decreased potassium – hypokalaemia

Values in the range 3.0-3.4 are common, and may remain unexplained even after investigation. Below 3.0, the cause needs to be found.

• Drugs diuretics: thiazides, loop diuretics purgatives antibiotics: some penicillins, PAS, gentamicin steroids

vit B12, folate, iron

• Liquorice • Diarrhoea and vomiting • Metabolic alkalosis • Corticosteroid excess � Conn's syndrome

Cushing's syndrome steroid medication

• Oedematous states � hepatic failure renal disease congestive heart failure

• Anorexia nervosa/bulimia

Potassium, urine

specimen: 24-hour urine, no preservative

ref. range: 30-130 mmol/day


The daily output depends on dietary intake but is commonly about 60-80 mmol/day.

When there is hypokalaemia, normal renal and adrenal function will reduce output to <30 mmol/day after 2-3 days. A higher value is consistent with adrenocortical excess (e.g. Conn's syndrome), vomiting or diuretic therapy.

With hyperkalaemia, normal homeostatic mechanisms should raise output to >130 mmol/day.

PR (prothrombin ratio)

)poolplasmanormal(PCT)patient(PCT

=PR

The term prothrombin ratio (PR) is still retained when referring to the extrinsic pathway test for Factors II, VII, IX, X when the patient is not on a vitamin K antagonist such as warfarin. It is used for evaluating coagulation disturbances in liver dysfunction and clotting factor deficiency due to vitamin K depletion. For practical purposes, PR and INR are the same test.

For monitoring warfarin therapy, see INR (international normalised ratio).

PRA (plasma renin activity) see Aldosterone and renin, plasma


Precision

see Imprecision Variation

Predictive value The predictive value of a test gives the probability that it will give the correct answer for a population. It combines sensitivity or specificity of the test with prevalence of the condition being tested for.

A test with a positive predictive value of 80% for a population, will give 80% true positives and 20% false positives.

A test with a negative predictive value of 97% will give true negatives in 97% and false negatives in 3%.

Pregnancy reference ranges

Pregnancy has a profound effect on many reference ranges.


Effect of Pregnancyalbumin decreased by 10 g/Lalkaline phosphatase steady increase up to 400 u/L by end of 3rd trimester (from placenta)AST may increase 10-15 u/Lblood volume increases 20-30%cholesterol on average increases 40% but can be double its

non-pregnant levelcreatinine clearance increasesglucose in urine glycosuria is common in healthy non-diabetic women

because of the drop in renal threshold during pregnancyESR steadily increases, up to 30-60 mm/hr in 3rd trimesterfructosamine is 5-10% lowerhaemoglobin decreases due to haemo-dilution by increased plasma

volume. 100 g/L is the approximate lower limithCG rises to a peak of 40,000-300,000 units by 8-10 weeks

and then falls back to a plateau some 60% loweriron-binding serum iron-binding capacity increases markedlyoestrogens increase to very high levels throughout pregnancypotassium rises from a mean of 4.3 in the 1st trimester to 5.9 in the

2nd and 3rd trimestersprogesterone increases throughout pregnancyprolactin increases throughout pregnancy to levels of up to 10000 U/Lprotein in urine up to 0.3 g/dayT4 (free) decreases up to 20% in late pregnancytriglycerides considerably elevated due to Increase in the VLDL

fraction. Serum is often milky in appearance because ofthis, a finding first noted by Virchow in 1847

TSH often falls in 1st trimester but returns to non-pregnantlevels in 2nd to 3rd trimester

urea decreases due to increased glomerular filtration rateuric acid decreases except in association with hypertension

(further details under uric acid)white cell count total count increases up to 15-18,000 due to increase

in neutrophils

Pregnancy tests


see hCG (human chorionic gonadotrophin)

Pregnanediol, urine

The old method for assessing progesterone, now replaced by serum progesterone.

Prevalence

The prevalence of a disorder is the number/100,000 of a population who have it at a given time.

The incidence is the number of new cases/year.

Primidone see Mysoline (primidone)

Procainamide see Antiarrhythmic drugs

17-OH progesterone see 17-hydroxy progesterone (17-OHP)


Progesterone specimen: serum

ref. range: (adult women on days 20-23 of 28-day cycle):

nmol/L

0-6 not indicative of ovulation 6-10 possibly ovulating10-25 probably ovulating25-80 ovulating

• To detect ovulation a specimen is taken 6-9 days after presumed ovulation, i.e. days 20-23 of a 28-day cycle. Serum levels rise sharply during the luteal phase to reach a plateau. See diagram under FSH.

• Because hormone release is episodic, levels can vary considerably throughout the day.

• Pregnancy � levels rise steadily to reach a peak of 200-700 nmol/L by term. • Ectopic pregnancy � the diagnosis of ectopic pregnancy is supported by a

level below 15 nmol/L in the presence of symptoms.

Prolactin specimen: serum ref. ranges: adult female 40-600 mU/L adult males 30-450 mU/L

Specimens should be collected at least 3 hours after awakening. Elevations of up to 1000 can usually be ignored or even up to 2000 in normally menstruating women. Repeat sampling 30 and 60 mins after the first specimen will help show up elevations due to stress alone. Prolactin levels above 5000 are almost always associated with prolactinomas or pregnancy.

In women, hyperprolactinaemia is an important factor in infertility, amenorrhoea and galactorrhoea (though 2/3 of women with galactorrhoea have a normal serum prolactin).


In men, hyperprolactinaemia lowers testosterone levels and is an uncommon cause of impotence or galactorrhoea as well as infertility.

Causes of hyperprolactinaemia

Physiological • stress • sleep • pregnancy � starts to rise at 6 weeks, peaks at up to 10,000 mU/L by term. • lactation � peaks occur during episodes of breast-feeding with levels up to

5000 mU/L. Prolactin is essential for normal lactation. • early morning collection � trough levels occur late morning. • eating � small rises

Drugs

� psychotropics � cimetidine � metoclopramide � tricyclic antidepressants � methyldopa � opiates � reserpine � haloperidol � oestrogens, including oral contraceptives � androgens

Pathological • pituitary adenomas and micro-adenomas • other hypothalamic-pituitary disorders • polycystic ovary syndrome • hypothyroidism • renal failure • seizures • anorexia nervosa • Addison�s disease • hypoglycaemia • idiopathic


Prostate cancer – histological grading

Prostate cancer is graded using the Gleason system based on the glandular pattern seen microscopically. The predominant pattern is selected and given a grade of 1 to 5 and the second commonest pattern is also given a grade of 1 to 5. The two grades are added to give a Gleason score of 2 to 10.

A Gleason score of 2-4 is a low grade tumour, 5-7 is intermediate grade, 8-10 is high grade. Higher scores usually mean a more aggressive tumour.

The Gleason score and the clinical stage of the tumour are predictive of long-term outcome.

Prostate specific antigen see PSA (prostate specific antigen)

Prostatic acid phosphatase (PAP) see Acid phosphatase, prostatic (PAP)

Protein electrophoresis see Electrophoresis (EPP) of serum proteins


Protein C specimen: plasma (citrate)

ref. range: 70-120%

Deficiency of Protein C is an inherited cause of hypercoagulability (qv) and is found in about 5% of cases of venous thromboembolism. The incidence of the deficiency is 1:5000 - 1:15,000. Approximately half of these will develop a thrombosis by the 6th decade. Inherited deficiency is usually an indication for long term anticoagulation.

Severe homozygous deficiency is associated with purpura fulminans in neonates.

Acquired causes of Protein C deficiency are liver disease, warfarin therapy, vitamin K deficiency.

see Hypercoagulability

Protein S specimen: plasma (EDTA)

ref. range: 70-130%

Deficiency of Protein S, a cofactor for activated Protein C, is an inherited cause of hypercoagulability (qv) and is found in up to 5% of patients with inherited thrombolic disease. The lower end of the reference range is not well defined.

Acquired causes of Protein S deficiency are liver disease, warfarin therapy, vitamin K deficiency, oral contraceptives, pregnancy.


Proteins, total, serum

specimen: serum

ref. range:

Age g/L0-6 mths 45-756-12 mths 50-751-2 yrs 55-75>2 yrs 60-84

total protein = albumin + total globulin

Total proteins, consisting of albumin and globulins, is a crude test, but a raised value can be a pointer towards raised immunoglobulins; a low value can be due to reduced albumin or globulins or both. Variations in protein concentration can be due to dehydration, diuretics, fluid retention or diurnal changes. On changing from the recumbent to the upright position, fluid is redistributed to tissues from the circulation causing an increase of up to 10% in protein concentrations.

Protein-binding in serum Many serum constituents exist in two forms, a protein-bound form, usually to an alpha or beta globulin or albumin; and a free form often a tiny percentage of the total but this is the metabolically active form. Examples of protein-bound constituents are thyroxine, tri-iodothyronine, cortisol, testosterone, vitamin B12, iron, copper, calcium � and many drugs.

Proteins, urine (proteinuria) specimen: 24-hour urine, no preservative

ref. range: <0.2 g/day � but see benign proteinuria below

Test methods


These depend on the clinical situation �

• Urine dipstick, as part of routine urinalysis This is a semi-quantitative test with proteinurias divided into 4 categories.

g/L

trace 0.1-0.5small 0.5-1.0moderate 1.0-2.5large >2.5

• Total protein concentration on spot urine � this gives a more accurate measurement than a dip-stick and also detects non-albumin proteins such as free light chains.

• Total protein concentration on spot urine � this gives a more accurate

measurement than a dip-stick and also detects non-albumin proteins such as free light chains.

• 24-hour protein quantitation � this test is used as follow-up when a dip-stick

shows 1+ (or more) positive, or when monitoring known proteinuria. • Urine microalbumin � a sensitive test measuring small quantities of albumin

in the range 0.01-0.20 g/L. The test is used as an early indication of diabetic nephropathy. see Microalbumin

• Electrophoresis of concentrated urine � used mainly in detection of free light

chains (Bence Jones protein). Renal proteinuria

Causes include the whole differential diagnosis of renal disease.

Glomerular proteinuria is by far the most common and serious type. The protein is predominantly albumin and when daily output >3 g/day, nephrotic syndrome


develops comprising oedema, albuminuria and hypoalbuminaemia. Serum lipids become elevated.

In tubular proteinuria, electrophoresis shows a non-selective pattern with bands representing the wide range of normal serum proteins normally reabsorbed by the tubules. Causes include drugs, inherited disease (e.g. Wilson's disease), autoimmune disease (e.g. SLE) or chronic infection.

Proteinuria of >1.0 g/day requires renal investigation including consideration of renal biopsy.

Benign and non-renal proteinuria

40% of our routine urinalyses show a trace or more of protein and most of these are benign.

Causes include:

• infection • fever • stress • exercise • heart failure • orthostatic proteinuria, found particularly in young men, disappears when the

patient is recumbent. Protein is absent from a morning specimen collected on first getting up.

• iodiopathic

24-hour protein in these is usually <0.5g/day. Levels of 0.2-0.5g/day (or even up to 1g/day) cannot be described as normal but often remain of unknown aetiology when found as isolated abnormalities. Intensive follow-up is usually unrewarding. Nevertheless, check on serum creatinine and urine culture and microscopy are required and repeat 24-hr urine in 3-12 months unless other signs or symptoms indicate need for earlier follow-up.


Proteus Proteus species are gram-negative enteric bacilli causing urinary infections and a variety of other infections, particularly in patients with impaired host defences. Treatment is based on antibiotic susceptibility results. Recurrent urinary infections with Proteus can be difficult to eradicate and should raise the possibility of the presence of renal calculi.

Prothrombin mutation (20210G-A)

The prothrombin gene mutation 20210G-A, found in 1-3% of the population, is associated with levels of prothrombin which exceed those in the normal population by an average 30%.

Clinically the mutation is associated with

� thrombophilia

� 3-6 fold increase in VTE

� cerebral vein thrombosis

� myocardial ischaemia in patients age <50

Prothrombin ratio see PR (prothrombin ratio) and INR

Protoporphyrins see Porphyrias


PSA (prostate specific antigen) specimen: serum

ref. range: <50 yrs <2.5 µg/L50 - 60 <3.560 - 70 <4.5>70 <6.5

PSA, an enzyme that liquefies the seminal coagulum, is found only in prostatic tissue and is an excellent tumour marker for monitoring treatment and progress of prostatic carcinoma.

Diagnostically it should always be requested when a patient presents with urinary outflow obstruction or when DRE (digital rectal examination) shows a hard, asymmetric or abnormally enlarged gland.

Controversy surrounds the use of PSA as a screening test, however, and the usual recommendation outside the United States is that PSA should not be offered to asymptomatic males unless they specifically request it � and if they do, they need to understand the diagnostic and therapeutic implications of an elevated level.

Some centres measure the free fraction as well as total PSA, a higher free/total ratio, e.g. >0.2, being more suggestive of benign enlargement.

PSA in benign prostatic conditions

In BPH (benign prostatic hypertrophy) the PSA is sometimes elevated but seldom above 10 µg/L. The PSA velocity (annual rate of rise of PSA) is usually less than in Ca prostate and a patient who chooses watchful waiting of a level below 10, may use PSA velocity as a deciding factor before requesting prostatic biopsy. Allowance must be made for a biological variation of 10-15% when observing serial PSA levels.


In prostatitis, the PSA can be elevated as high as 50 µg/L but will fall back to its natural baseline after successful treatment.

DRE (digital rectal examination) may cause a 5% elevation, occasionally more, falling back to the baseline over a few days.

PSA levels also rise for up to 24 hours after sex, especially in older men.

PSA in prostatic cancer

Up to 30% of patients with early Ca will have a PSA within the reference range. Annual monitoring, as recommended by US urologists, would show a rising PSA in this group.

A PSA above the upper reference limit but below 10 is in a zone of uncertainty where only a biopsy will provide the diagnosis. Annual monitoring rather than biopsy will be the chosen option for some patients.

When the PSA has risen above 10, the probability of carcinoma is rising steeply and most patients proceed to biopsy.

The natural history of prostatic cancer

Prostatic Ca is usually an indolent tumour presenting in later life and most affected males die with the tumour rather than of it.

It is a common tumour � 40% of males over the age of 75 are affected when examined at autopsy.


It is the cause of death in 5% of males, the commonest male tumour after Ca lung; the average age at death is 75.

Treatment of prostatic cancer

If treatment, whether radiotherapy or surgery, were easy and free of complications there would be no controversy. The problem lies with the relatively high complication rate and their unpleasant nature � incontinence and impotence � and this is why some patients take the chance that their life will not be significantly shortened, even without treatment.

Summary of indications for measuring PSA

• monitoring known prostatic Ca � PSA should be <1 after prostatectomy • searching for a primary in disseminated malignancy • symptoms of urinary tract obstruction • abnormal prostate on DRE • family history of Ca prostate • the patient requests it and understands the implications. A patient above the

age of 75 should probably be discouraged from measuring his PSA as a "check", especially if other significant chronic illness is present.

Pseudomonas aeruginosa

In general practice, Pseudomonas is encountered mainly in chronic otitis externa where it usually responds to local toilet and topical polymyxin. The most commonly used agent in the past, Chloromyxin, which contained polymyxin B, is no longer available. Another ear preparation Colymycin S Otic, containing colistin which has the same spectrum of antibacterial activity as polymyxin, is currently the most widely used topical preparation for Pseudomonas otitis externa.


P. aeruginosa is often recovered from ulcer lesions on the lower limbs of the elderly. It is frequently a coloniser rather than a pathogen in this situation. If, however, the gram-stain reveals many WBC's with gram-negative bacilli and the ulcer has deteriorated clinically Pseudomonas may be the cause of infection. In this instance ciprofloxacin treatment may be indicated. Pseudomonas can cause more serious infections in burns, in immuno-compromised patients and in nosocomial infections. In these situations, early treatment with carefully selected antibiotics is required because of the organism�s pathogenicity and resistance to a variety of agents.

Psittacosis see Chlamydia psittaci

PTH see Parathyroid hormone (PTH)

Pus swabs see Skin and wound swabs


Pyrophosphate

Calcium pyrophosphate is found in pseudogout either as crystals in synovial fluid or as deposits resembling gouty tophi in periarticular tissues.

see also Synovial aspirate

Pyuria, sterile see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections)

Q

Q Fever specimen: serum

A rickettsial disease due to Coxiella burnetii, an obligate intracellular gram-negative bacillus. It may present as an atypical pneumonia in someone who has had recent contact with domestic animals overseas. Not present in New Zealand.


Antibody levels can detect current or recent infection.

Quinidine see Antiarrhythmic drugs.

R

RA see Rheumatoid arthritis (RA)

Rapid smears

Please contact Histology Department


RAST (Radioallergosorbent test)

specimen: serum

Individual allergens required must be listed. RAST screens for multiple allergens are not done because of the high cost per test.

RAST tests use the patient�s serum to diagnose specific allergies by identifying the presence of an IgE antibody against that allergen. They are used as a second-line investigation, the first-line being the standard battery of skin tests (qv). Specific indications for RAST tests are:

• severe skin disease • non-reactive skin • hyper-reactive skin (dermographism) • skin test might be hazardous, e.g. penicillin, bee or wasp venom sensitivity • very young children • patients on antihistamines or sympathomimetics that cannot be stopped for

skin tests.

The list of specific allergen tests includes:

aspergillus grass mix bee venom horse hair blue mussel latex cat dander mould mix cheese peanut cow's milk penicillin G dog fur shrimp dust mite soya bean egg wasp venom fish wheat gluten yeast


RBC = red blood cell

Reactive arthritis see Arthritis, reactive

Reactive hypoglycaemia see Hypoglycaemia

Red cell antibodies

specimen: serum

Indications:

� pregnancy - a screen test is followed by specific identification if the screen is positive

see Bilirubin, total � haemolytic disease of the newborn � autoimmune haemolytic anaemia see also Coombs test


Red cell enzymes

specimen: blood (heparin)

Screening tests are available for:

• G6PD (glucose-6-phosphate dehydrogenase) • pyruvate kinase • pyrimidine-5-nucleotidase

Quantitative assays on these and other enzymes are available as follow-up.

Red cell mass (volume)

Used in the diagnosis of polycythaemia vera.

see Polycythaemia

Blood volume

Red cell osmotic fragility see Osmotic fragility of red cells

Red cell survival

The patient's red cells are labelled with 51Cr and their survival in the circulation determined.


This test is sometimes used in suspected haemolysis. If there is significant loss of blood from the gastrointestinal tract, tagged red cells can be detected in the stools.

Reducing substances in faeces

specimen: fresh sample of faeces in small jar delivered to lab as soon as possible, stored in fridge if delay is unavoidable.

The test is a simple qualitative test for reducing substances which include lactose, glucose and fructose but not sucrose.

Acquired lactase deficiency, in which the disaccharide lactase is not digested, presents as frothy diarrhoea with failure to thrive in infants after infectious diarrhoea.

The diagnosis can be confirmed by improvement after withdrawal of lactose from the diet.

Reference ranges and the concept of normality

In the dawn of laboratory medicine, before 1969, before the invention of the biochemistry Auto-Analyser or the flow-through haematology blood counter, we believed a sharp line divided normal from abnormal results. This was always too simplistic. Some results are almost certainly normal, others almost certainly abnormal, and separating these is a broad grey zone where interpretation depends on consideration of clinical history and findings and a host of other variables.

The term �normal range� was replaced by �reference range� (or �reference interval�) to indicate that we make no judgement on whether a result is normal. We simply provide a range that covers the values of 95% of a group (e.g. blood donors) who are


apparently disease-free and similar to the patients we are dealing with in terms of age, gender, etc and we �refer� to that range when trying to decide whether our patient�s result is indicative of, or consistent with, a particular diagnosis.

Most of the interpretative notes in this handbook are directed towards defining the variables that influence this decision. Whenever there is doubt about the significance of a result, the test should be repeated immediately if the clinical situation demands it or in a week or a month or even a year if there is no urgency. The temporal pattern provides an extra dimension by showing whether a result is increasing, decreasing or staying the same, whilst at the same time the clinical picture has the opportunity to move in one direction or the other.

Some reference ranges, such as those for cholesterol or uric acid, are not 95% population ranges but "ideal" ranges that we should strive to attain.

see also introductory notes

Reiter's disease see Arthritis, reactive

Renal calculi

Most calculi are of unknown origin but four aetiologies need to be remembered.

• hypercalcaemia � check serum calcium, vitamin D • uric acid excess in urine • cystinuria


• mixed "triple-phosphate" stones, often due to chronic, occult urine infections with gram-negative bacteria such as Proteus.

The reason for analysing calculi is to detect pure uric acid (5-10% of all stones) or cystine. In the case of uric acid stones, the causes of increased uric acid (qv) excretion need to be looked for. Allopurinol is effective in preventing further stone formation.

The remaining 90% of stones are composed of calcium oxalate or phosphate and in half of these there is hypercalciuria due to increased intestinal absorption of calcium. A 24-hr urine should be analysed for calcium, phosphate, urate and oxadate.

Renal glycosuria see Glycosuria

Renal screen tests

a simple screen - serum creatinine - urine for : microscopy protein culture

Creatinine clearance (qv) is not a useful screen test because of the inaccuracies associated with 24-hour urine collections.

Renal tubular acidosis

Because of tubular defects, the kidney has impaired ability to secrete an acid urine.


The patient may present with renal calculi and show electrolyte disturbances including low potassium, low bicarbonate, high chloride.

A useful screen test is to measure the pH of a spot urine on first rising. A pH <6.0 suggests normal acidification. An acid load test is used for follow-up.

Renin see Aldosterone and renin, plasma

Reptilase clotting time

Reptilase is a thrombin-like enzyme isolated from snake venom which is capable of clotting fibrinogen. It is used to detect dysfibrinogenaemias.

Reticulin antibodies

specimen: serum

ref. range: not present

see Coeliac disease (gluten sensitive enteropathy) for interpretation

Reticulocyte count


specimen: whole blood (EDTA)

ref. range: absolute count 10 � 100 x 109/L percentage count 0.1�3.0% in non-anaemic subjects

Absolute counts are preferred to percentages because they are independent of anaemia. Polychromasia is the morphological indicator of increased reticulocytes.

The reticulocyte count is increased in:

• chronic or acute blood loss • haemolytic anaemias • deficiency anaemias treated with iron, B12 or folate (treatment response). • marrow infiltration

A reduced reticulocyte count suggests a hypoplastic basis for an anaemia.

Rhesus incompatibility see Haemolytic disease of the newborn

Rheumatic fever

New Zealand still has a high incidence of acute rheumatic fever with Maori and Pacific Islanders making up 84% of the total. 60% of cases are in the 5-14 age group. It is a notifiable disease. Diagnosis is based on the revised Jones criteria:

major manifestations minor manifestations carditis clinical polyarthritis previous rheumatic fever


chorea or rheumatic heart disease erythema margination or arthralgia subcutaneous nodular fever laboratory raised ESR, or CRP, or WBC ECG prolonged P-R interval evidence of streptococcal infection � increased streptococcal antibodies � positive throat culture for GpA streptococcus � recent scarlet fever

The diagnosis requires:

� two major criteria or � one major and two minor criteria plus evidence of streptococcal infection

Absence of evidence of streptococcal infection makes the diagnosis doubtful. A serum sample should be collected for streptococcal antibodies whenever the diagnosis of rheumatic fever is suspected and a second sample collected at least two weeks later, looking for rising titres.

see Streptococcal antibodies (ASK, ASOT, ADNAse)

Rheumatoid arthritis (RA)

The commonest of the connective tissue diseases with an incidence of 1-2% in the general population. The American Rheumatology Association (1982) recommends that the diagnosis be applied to those who are positive for four of the following seven criteria:


• rheumatoid factor (positive in 80%) • morning stiffness • arthritis of hand joints • symmetric arthritis • arthritis of 3 or more joint areas (of 14) • rheumatoid nodules • radiographic changes

Note that 20% of patients with rheumatoid arthritis are negative for rheumatoid factor.

see also Rheumatoid factor (RF)

Rheumatoid factor (RF)

specimen: serum ref. range: latex test <20 u/ml Rose-Waaler <30 u/ml

Rheumatoid factor is an antibody, or rather a group of IgM, IgG and IgA antibodies, directed againtst IgG. Most methods detect the same IgM rheumatoid factor but specificities vary somewhat and for this reason a test that is positive in one laboratory may be negative in another and the quantitations may differ.

2% of the healthy population are positive for RF, rising to 5-10% in the elderly.

In rheumatoid arthritis (RA) qv, RF is present in only 80% of cases. RF on its own does not signify rheumatoid arthritis and conversely a clear clinical presentation of RA does not require RF to establish the diagnosis. RF is often absent during the first


6 months of disease. Higher levels tend to be associated with more aggressive disease.

Conditions, other than RA, with a high incidence of RF are:

• Sjogrens (90%) • SLE (30%) • other connective tissue disorders • chronic inflammatory/infectious disorders • malignancy

Ringworm see Dermatophytes

Rochalimaea henselae see Cat scratch disease

Rose-Waaler test see Rheumatoid factor (RF)

Ross River fever


Although not contracted within NZ, this febrile illness, due to an arbovirus, may be found in patients who have recently returned from Australia. Antibody tests can be arranged.

Rotavirus specimen: fresh faeces

Rotavirus is the commonest cause of diarrhoea in young children � 50% of children under 5 hospitalised for gastroenteritis are infected with rotavirus. Essentially all children are infected by the age of 3 with the peak incidence between 6 and 24 months. Adult infections are much less frequent. There is a clear winter peak. Spread is by the faecal-oral route. It has a short incubation period, 24-72 hours.

Symptoms may be severe but usually settle within 7 days with oral fluid and electrolyte replacement.

RPR (rapid plasma reagin) test see Treponemal serology (STS, serological tests for syphilis)

Rubella

specimen: serum tests: IgG for immune status IgM for current infection

ref. ranges :


Units/mlIgG <5 non-immune

5-11 equivocal>11 immune

IgM detectable for about 3 monthsduring and immediately afterinfection

Immune Status

MMR (measles/mumps/rubella) vaccine is recommended for all children as an SC injection at one year followed by a booster at age 11.

The person with an IgG antibody level >10 µ/ml, can be assumed to have solid immunity.

With levels between 5 and 10, immunity probably exists but a rubella vaccine booster is recommended except in pregnancy when the booster should be delayed till after delivery.

Below 5, immunity is either non-existent or slight and revaccination is indicated � though as above, not in pregnancy.

It is essential that pregnant women found to be non-immune be vaccinated after delivery. A big proportion of cases of congenital rubella occur in women who have had previous pregnancies.

Infection during pregnancy

Because 85% of mothers infected during the 1st trimester give birth to infants with congenital defects (eyes, ears, heart, brain), termination of pregnancy must always be discussed when infection has been established.


The mother who has had contact with suspected rubella and whose immune status is susceptible or unknown, should immediately have a blood collected for IgM and IgG antibodies with at least one more specimen 3 weeks later.

If the woman develops signs or symptoms consistent with rubella, IgM antibodies should be collected at weekly intervals for 3 or 4 weeks to check for presence of IgM and subsequent rise in titre which will confirm infection.

Final confirmation is through detection of rubella RNA in a placental biopsy or foetal blood.

S

S. = serum

Salicylate specimen: serum ref. range: therapeutic 1.0-2.0 mmol/L toxic >3.6 mmol/L


Salivary gland antibodies

specimen: serum

Positive in 50-70% of Sjogren�s syndrome, otherwise rare.

Salmonella antibodies (Widal Test)

specimen: serum

A test of limited value in the diagnosis of typhoid fever, blood culture being the preferred diagnostic method.

Interpretation

O antigens titre >1:160 and rising sharply over 7-14 days suggests current infection. H antigen >1:160 suggests immunity Vi antigen high titre sometimes indicates the carrier state.

Titres can be non-specifically elevated in diseases not caused by Salmonella and vaccination can give positive titres.

Salmonella culture specimen: faeces for diarrhoea

blood culture for suspected typhoid fever


Enterocolitis

Salmonella species make up 15% of the pathogens cultured from faeces in this laboratory, the main reservoir being domestic animals (including poultry and eggs) and infected humans, both symptomatic and carriers. Species causing enterocolitis include S. typhimurium, S. choleraesuis and S. enteritidis. In healthy persons the episode usually resolves in 2-3 days. Patients with impaired defences may require antibiotic treatment, usually with cotrimoxazole, amoxycillin or ciprofloxacin. The chronic carrier state can be treated with ciprofloxacin.

Salmonellosis is a notifiable disease.

Typhoid Fever

Only a few cases occur in Auckland each year, S. typhi being the usual cause or occasionally S. paratyphi A or B.

During the early stages, diagnosis is by blood culture which should be done repeatedly when clinical suspicion is strong. From the second week on, faeces cultures may be positive.

Sarcoidosis

A systemic disorder of unknown cause characterised by non-caseating granulomata. Diagnosis usually requires histological examination of lung, skin, lymph nodes or liver.

Serum ACE (angiotensin converting enzyme) is elevated in 2/3 of patients but the test is not specific enough to be of diagnostic value, nor does it have prognostic significance.


Serum calcium may be elevated.

Saturation, iron see Iron-binding capacity (IBC) and saturation

Scabies

Caused by the mite Scarcoptes scabiei and transmitted by direct skin to skin contact. Transfer from clothes is possible but only if worn by infected people immediately beforehand.

Incubation period 2-6 weeks without previous exposure but only 1-4 days in those who have been infected before.

Burrows are characteristic in scabies. These consist of skin-covered ridges 0.5 - 1.0 cm in length, often with a small vesicle at the end.

The diagnosis is usually made clinically but where microscopic examination of scrapings is required, this can be arranged. A few drops of paraffin oil are placed on the affected area and the lesion scraped removing skin and the mite. Treatment is usually with permethrin 5% cream. Gamma benzene hexachloride 1%, cream or lotion, and crotamiton 10%, cream or lotion, are alternatives. Pruritis may persist for some time after successful treatment.

Schilling test


The Schilling test used to be used more often in the investigation of vitamin B12 deficiency than it is now when pernicious anaemia can be diagnosed by simpler tests.

It measures the absorption of orally ingested labelled B12 with and without added intrinsic factor. Normally >10% of the orally administered vitamin B12 is excreted in the urine. An intramuscular loading dose of vitamin B12 is given to ensure that stores are replete.

In either pernicious anaemia or malabsorption, <10% is excreted but in the case of PA, the added intrinsic factor corrects the abnormality.

see also Pernicious anaemia Vitamin B12

Schistosomiasis specimens : � random faeces � urine, full volume (not just an aliquot) preferably collected between noon and 3pm when there is peak egg

excretion � serum for antibody tests

Request examination for schistosome ova. Eggs may be found in urine and stool as early as five weeks after infection. Patients with a low worm burden may have few or no eggs in urine or stool.

Although over 200 million people in Africa, the Middle East, S. America and the Caribbean are infected with these blood flukes, schistosomiasis is rare in travellers to these areas. Infection requires skin contact with contaminated fresh water as in swimming or wading bare-foot in paddy fields, water-holes, local streams, etc. The infective form penetrates human skin, passes through a migratory phase in the lung and liver and then moves to its final habitat in the portal venous system (S. mansoni)


or urinary bladder venous plexus (S. haematobium). Adult male and females live for 5-10 years.

Many New Zealanders have acquired infection in Lake Malawi in South East Africa. It is stated in some travel guides that this lake is free of infection risk. This is not the case and travellers should be advised against swimming in this lake.

The usual problem is the traveller who requires reassurance. Examination of faeces for the highly characteristic ova; urine for ova and red cells; serum for serology, and perhaps liver function tests, are adequate for this purpose.

Where more serious investigation is required, up to 6 specimens of urine and faeces should be examined. Further investigation might include appropriate tissue biopsies (rectum, bladder, liver).

Positive serology indicates present or past infection. Persons with negative stool and/or urine tests but positive serology require treatment to avoid the uncommon but catastrophic spinal cord complication of transverse myelitis.

Treatment with praziquantel and follow-up are best managed by those with experience treating schistosomiasis.

Scleroderma, diffuse

Also called systemic sclerosis, this is a connective tissue disease characterised by diffuse cutaneous and/or systemic fibrosis.

Raynaud's phenomenon is present in 95% of cases.

It has an incidence of about 1:50,000


Tests that are often positive include:

ANA (95%) usually with a nucleolar pattern.

RF (25%)

ENA anti Scl-70 (30%)

Scleroderma, limited

Previously called CREST syndrome:-

Calcinosis

Raynaud's phenonemon

Esophageal dysmotility

Sclerodactyly

Telangiectasia

Tests that are often positive include ANA (80%) usually centromere pattern.

Scoline (suxamethonium) sensitivity

This autosomal recessive disorder renders the carrier apnoeic for an abnormally long period after administration of scoline. Family members of an infected individual should be tested. The dibucaine number is an additional test used in identifying carriers.

see Cholinesterase


Selenium

specimen: plasma or whole blood (heparin)

ref. range: plasma 630-990 nmol/L (50-80 µg/L)

Selenium is an antioxidant and is an essential trace element in humans and animals, entering the food chain through plants. In the Keshan province of China, an endemic cardiomyopathy has been attributed to the region's severe soil selenium deficiency.

It has been suggested that lesser degrees of deficiency contribute to health problems in western countries including subfertility, cancer and heart disease. Although New Zealand soils are low in selenium, documented human deficiency is rare except when there is another cause such as prolonged parenteral nutrition.

Brazil nuts are a rich natural source of selenium.

Seminal fluid

A. Post-vasectomy specimens

This is a test for sperm count only, not motility. The specimen should be delivered to the laboratory on the day of collection but without the urgency necessary for fertility specimens.

Most post-vasectomy specimens have a zero sperm count but a small percentage have a low count of non-motile spermatozoa even months after successful surgery. They are believed to be sequestered spermatozoa stored in the recesses of seminal vesicles or other parts of the male GU system.


B. Infertility specimens

The following written instructions can be given to the patient.

Instructions for the collection of semen for sperm count 1. The test is performed only on week days, not Saturday or Sunday. 2. The specimen should be delivered to the main laboratory within 2-3 hours of

collection and preferably before 3pm. Many people collect the specimen at home at 7-8am and deliver the specimen before work.

3. You should refrain from sexual intercourse or ejaculation for 3 days before

collecting the sample. 4. The specimen should be obtained either by masturbation or by having intercourse

in the usual way (do not use a rubber sheath or other male contraceptive) and withdrawing just before ejaculation. Ejaculate into the collection jar provided which must be kept nearby and warm.

5. It is important that the whole of the specimen is collected. If some of the

specimen is lost at the time of collection, this should be noted. Interpretation

normal doubtful probably infertile

volume (ml) 2-6 1.5-2.0 <1.5count (million/ml) 20-250 10-20 <10motile sperm (%) >50 35-50 <35

Volume correlates least well with fertility. A high volume (>6ml) can be associated with oligospermia or a low volume with normal fertility.


Count Even low counts do not absolutely exclude fertility.

Motility Reduced by exposure to temperatures above or below body

temperature. 24 hours at room temperature kills all motility.

Morphology Normally less than 20% are defective.

If an initial sample suggests sub-fertility, two further specimens should be collected over a 2-3 week period with no intercourse or ejaculation for at least 3 days before specimen collection.

Care should be taken in diagnosing �sub-fertility� on the basis of seminal fluid analysis, particularly when the abnormalities are not marked.

Sensitivity/Specificity

As applied to a laboratory test, sensitivity refers to the ability of the test to detect a condition or analyte. A test with a sensitivity of 97% will fail to detect the condition in 3% of those who have it, i.e. there will be 3% false negatives.

Sensitivity tends to be achieved at the expense of specificity.

Specificity is the ability of a test to give a positive result only when the condition or analyte being tested for is present. A test with a specificity of 97% will give a false positive result in 3% of persons tested. A test must have a high degree of specificity when searching for an important or uncommon condition in a large population, e.g. when searching for HIV in a community.


Serotonin

In carcinoid tumours (qv) the plasma serotonin levels are elevated but 24-hr urinary 5-HIAA is the test used in diagnosis.

Sex hormone binding globulin see SHBG (sex hormone binding globulin)

SGOT the old name for AST

SGPT the old name for ALT

SHBG (sex hormone binding globulin)

specimen: serum ref. ranges: adult female 50-80 nmol/L adult male 40-60 nmol/L

SHBG is a serum globulin that binds testosterone and, to a lesser extent oestradiol. On its own, it has little diagnostic value but it is required when measuring the biologically active free testosterone fraction as distinct from the 98% of total testosterone which is bound and inactive.

SHBG is increased by: oestrogens, pregnancy, androgen deficiency, thyrotoxicosis, cirrhosis.


It is decreased by: obesity, hypothyroidism, androgen excess, polycystic ovary syndrome, hirsutism.

Shift to the left see Neutrophils (polymorphs): neutrophilia

Shigella

specimen: fresh faeces

Shigella, the cause of �bacillary dysentery�, is predominantly found in third world countries where it is transmitted by contaminated food and water. In this laboratory, shigellae make up 4% of faecal pathogens. Children under 5 years are affected particularly.

Mild cases are treated with oral rehydration alone but more severe infections may require antibiotics � cotrimoxazole or ampicillin (not amoxycillin) or norfloxacin (adults only) � and IV fluids. Shigellosis is a notifiable disease.

Shingles see Varicella-zoster virus (VZV)


SI (systeme internationale) units

In 1975-77, New Zealand, Australian and UK laboratories switched from traditional mass units (mg/100ml) to SI units (mmol/L). United States laboratories have mostly retained mass units which may need to be converted when American patients present in NZ with results from back home.

conversionSI Unit mass unit factor

alcohol 1 mmol/L = 4.5 mg/100ml 0.22bilirubin 1 µmol/L = .06 mg/100ml 17.1calcium 1 mmol/L = 4 mg/100ml 0.25cholesterol 1 mmol/L = 38.5 mg/100ml 0.026creatinine 1 mmol/L = 11.4 mg/100ml 0.088glucose 1 mmol/L = 17.9 mg/100ml 0.056potassium 1 mmol/L = 1 meq/L 1.0protein 1 g/L = .1 g/100ml 10.0sodium 1 mmol/L = 1 meq/L 1.0triglyceride 1 mmol/L = 91 mg/100ml 0.011urate 1 mmol/L = 16.7 mg/100ml 0.060urea 1 mmol/L = 5.9 mg/100ml 0.17

to convert mg/100 ml to mmol/L: multiply by conversion factor.

to convert mmol/L to mg/100 ml: divide by conversion factor.

An advantage of SI units is that osmolality (in mmol/L) of serum or urine can be simply calculated by adding concentrations (in mmol/L) of the constituents, assuming all the main ones have been measured.

SIADH (syndrome of inappropriate ADH)

see Sodium (Na+), serum


Sickle cell test specimen: blood (EDTA or heparin)

Sickle cell haemoglobinopathies are hereditary disorders due to HbS, found in blacks of African descent. The homozygous state (sickle cell disease) causes a chronic haemolytic anaemia and during crises, episodes of pain and multi-system organ damage. Heterozygotes (sickle cell trait) are free of clinical disease and have normal red cell indices but HbS can be demonstrated by appropriate tests including Hb electrophoresis.

Sideroblastic anaemia

This is an acquired disorder of porphyrin metabolism seen in older patients and associated with anaemia, either microcytic or dimorphic. It is a preleukaemic condition and is part of the myelodysplastic (MDS) spectrum of disorders. The hallmark is a marked increase in bone marrow iron, ring sideroblasts on Perl stain in the bone marrow and an elevated ferritin. The disorder may be primary (in MDS) or secondary to drugs, particularly antituberculous therapy.

Sjogren's syndrome

A connective tissue disease characterised by salivary and lacrimal gland involvement resulting in dry mouth and dry eyes.

It may exist on its own or be associated with rheumatoid arthritis or other connective tissue disease.


Tests that are usually positive include:

ANA usually with a speckled pattern

RF (90%)

ENA (60%) anti SSA (Ro) or SSB (La)

Skin and wound swabs

When collecting the swab, aim to get pus or exudate from the base of an actively inflamed lesion. Remove scab if present and open infected blisters. Avoid getting bacteria from normal skin. 80% of skin/wound/pus swabs in the Auckland community grow Staph. aureus. Strep. pyogenes makes up most of the remainder. The latter is the usual pathogen in impetigo and cellulitis.

% susceptibilitiesfluclox amox-clav cefaclor pen eryth cotrim cipro tet

S.aureus¹ 93 93 93 12 85 99 100² 97S. pyogenes 100 100 100 100 99 99 — 83

1. There has been an increase in MRSA in Auckland from 0.2% in 1990, 0.7% in 1993. to 7% in 1998. MRSA is more common in South Auckland than in other areas of the region.2. Quinolones are not recommended for treating S. aureus infection because the MIC's are close to the cutoff for susceptibility and the common emergence of resistance.

Chronic leg and foot ulcers are commonly associated with vascular insufficiency, and, in the diabetic foot, with loss of pain and touch sensation. Swabs usually show a mixed growth of gram-positive cocci and gram-negative bacilli. Cellulitis confined to the rim of the ulcer can be treated with an oral agent such as amoxycillin-clavulanate but a spreading cellulitis, particularly in a diabetic foot, needs urgent admission for parenteral antibiotics.

All chronic ulcers require careful daily cleansing with warm saline and debridement of dead tissue down to a healthy base.


Skin biopsy A. Method

1. Excisional skin biopsy This technique should be used for:

• atypical pigmented lesions

• deep dermal/subcutaneous nodules

• where evaluation of margins is important

• where panniculitis (inflammation of subcutaneous fat) is suspected

2. Punch biopsy This technique is useful for:

• inflammatory dermatoses • suspected basal or squamous cell carcinomas prior to definitive

treatment

Excisional biopsy should be performed rather than punch biopsy if malignant melanoma is suspected. The punch biopsy should include subcutaneous fat. Crush artefact, when forceps are used to extract the biopsy, should be avoided. The specimen should be immediately placed in 10% formalin.

3. Shave biopsy

This usually results in epidermis only or epidermis and superficial dermis. Shave biopsy should not be used if there is any suspicion of malignant melanoma. In acral sites (soles of feet, palms of hands) usually only keratin is obtained in a shave biopsy.


4. Curettage This is the least satisfactory form of skin biopsy as the tissue may not be satisfactory for histology.

B. Site selection This is of critical importance particularly in:

• Inflammatory dermatoses � biopsy should be from a fully developed lesion and if the lesions are in different stages of evolution, multiple biopsies should be taken. Treated areas should be avoided.atypical pigmented lesions

• Vesiculobullous lesions, ulcers, pustules � biopsies should be taken from very early lesions and should include normal skin.

C. Direct immunofluoresence microscopy Biopsies should be submitted to the laboratory fresh on damp saline-soaked gauze in a specimen container packed in ice. The specimen needs to be snap frozen in the laboratory within 2 hours of the specimen being taken.

The pathologist should be contacted 24 hours prior to taking the biopsy to ensure rapid handling.

Skin scrapings for mycology see Dermatophytes

Skin tests for allergy

These tests require an appointment. A set of tests takes about 30 minutes.


Indications

For identifying trigger allergens in asthma, allergic rhinitis and contact eczema.

Where skin tests are not feasible, serum RAST (qv) tests for specific allergens can be used.

Preparation The patient must discontinue antihistamines or sympathomimetics for three days. Steroids and cromoglycate can be continued.

Method A drop of dilute allergen is placed on the skin; a needle prick through the drop introduces a minute amount of allergen into the dermis; if it encounters specific IgE antibodies bound to mast cells, histamines are released and a wheal and flare develop.

Allergens 16 allergen solutions and 2 controls are used.

• house dust mite 1 (D. pteronyssinus)

• plantain

• house dust mite 2 (D. farinae) • mixed tree pollen • cat hair • privet • dog hair • milk • horse hair • egg-white • feathers • peanut • mixed moulds • wheat • mixed grass pollens • +ve control (histamine) • perennial rye • -ve control (suspension

fluid) Interpretation


• A positive result does not always mean the patient will suffer an allergic illness when exposed to that allergen.

• A negative result does not entirely exclude sensitivity � these false negatives are more common in children under the age of 5.

• The food tests are the least reliable � a negative result does not exclude sensitivity.

• The mould mixture can give false negatives as it is not possible to include the full range of allergic moulds in the mixture.

• Privet is often blamed for allergies but positive tests are uncommon. More often a grass pollen is the cause of "privet allergy".

• If all results are positive, including the negative control, the patient has dermatographism which is not due to allergy.

• If the positive control (histamine) is negative, the patient is probably taking antihistamines.

• If all tests are negative (except the positive control), the patient is unlikely to have atopic disease

see also Bee and wasp venom allergy

Food allergy

Penicillin allergy

SLE (systemic lupus erythematosus)

A relatively common (1:1000) connective tissue disease which can affect a wide variety of systems and is characterised by auto-antibodies directed against nuclear components.

There is no single specific test but rather a list of diagnostic criteria. The American Rheumatology Association (1982) recommend that if four of the following criteria are positive, the diagnosis can be made:

• ANA positive (95%) • anti- DNA, or ENA Sm, or biological false positive VDRL


• haemolytic anaemia, or leukopenia, or thrombocytopenia • nephropathy (proteinuria >0.5 g/day) • arthritis • pleuritis or pericarditis • malar rash • CNS involvement (psychosis, seizures)

During active SLE, complement (C3 & C4) are reduced and the ESR is raised.

see also: ANA (antinuclear antibodies)

DNA antibodies (anti-double-stranded DNA)

ENA (extractable nuclear antigen) antibodies

Smear cells

These are lymphocytes which rupture in a blood film presenting a smeared appearance. They are typically found in large numbers in chronic lymphatic leukaemia.

Smooth muscle antibodies (SMA)

specimen: serum

SMA are present in high titre in 80-90% of autoimmune hepatitis, usually in association with positive ANA and raised total IgG. Transient low titre SMA elevations occur in other liver diseases and viral illnesses.

see also Hepatitis, autoimmune


Sodium (Na+), serum specimen: serum

ref. range: 135-148 mmol/L

Decreased sodium – hyponatraemia

Values in the range 130-134 are common and sometimes difficult to explain. Below 130, an explanation must be sought.

• fluid or electrolyte loss with inadequate electrolyte replacement � diarrhoea, vomiting, excessive sweating, post-operative losses, fistulae, parenteral fluid replacement with saline <0.9%.

• drugs � diuretics (particularly thiazides), ACE inhibitors, NSAIDs, carbamazepine, imipramine, amitriptyline, lithium, � and others

• oedematous states � cardiac, hepatic, renal • renal tubular disease � salt-losing syndromes • Legionnaire's disease and other chest infections • pseudo-hyponatraemia � hyperlipidaemias and paraproteinaemias • endocrine diseases � diabetes, hypothyroidism, Addison's disease,

hypopituitarism

SIADH � syndrome of inappropriate ADH, a common cause of hyponatraemia, including those where the sodium is very low (<125). Causes of SIADH include:

� carcinoma, particularly of lung � pulmonary infections � CNS disorders � drugs

The cause of the low serum sodium is water retention due to inappropriate secretion of ADH in the face of a serum osmolality below 270 mosmol/L.


The correct physiological response in this situation is inhibition of ADH secretion with formation of a dilute urine of osmolality <100 mosmol/L but in SIADH, urine osmolality is >100 and urine Na+ concentration is typically >20 mmol/L.

Diagnosis is based on exclusion of known causes of hyponatraemia and measurement of urine osmolality and Na+ concentration. Reducing water intake will usually correct the hyponatraemia.

Sodium, urine specimen: 24-hr urine, no preservative

ref. range: 40-220 mmol/day

In a well person, urine sodium output reflects dietary intake. A low output, <20 mmol/day, may be an indicator of a total body sodium deficit but interpretation requires consideration of all fluid and electrolyte parameters.

Somatomedin C see IGF-1 (insulin-like growth factor-1, somatomedin C)

Somatotropin see Growth hormone (HGH, somatotropin)

Specific gravity, urine


ref. ranges: random urine 1.002-1.030 24-hr urine 1.015-1.025 after 12-hr fluid restriction >1.025

This outdated measure of urine concentration has been replaced by urine osmolality (qv).

Specificity see Sensitivity/Specificity

Sperm antibodies

specimen: seminal fluid

Antibodies in seminal fluid are a marker for immunological male infertility.

Spermogram see Seminal fluid

Spherocytes


Spherocytosis is associated with haemolysis:

• congenital spherocytosis • autoimmune haemolytic anaemia • microangiopathic haemolysis • severe burns • after splenectomy

Splenectomy specimens

Pack in ice without fixative and forward to lab as soon as possible.

Sputum culture

Sputum is examined in three clinical situations:

Suspected TB Where infectious TB is a possibility, ZN stain and culture are essential. see Tuberculosis (TB) for more detail.

Pneumonia If the patient can produce sputum � often a problem � the examination is worthwhile provided it is collected before antibiotics are commenced.

Acute on chronic bronchitis A sputum examination is seldom useful though the matter is debated. In exacerbations of chronic bronchitis the important organisms are Strep. pneumoniae and Haemophilus influenzae. Moraxella (formerly Branhamella) catarrhalis may also be involved.


% susceptibleamox tetra cotr cefaclor amox-clav eryth pen

H. influenzae 81 99 91 100 100 0¹ —S. pneumoniae —² 71 67 —² —² 100 68M. catarrhalis 3 98 98 100 100 98 3

1. The newer macrolides roxithromycin and to a greater extent clarithromycin have activity against H. influenzae.2. While pneumococci with reduced susceptibility to penicillin are also less susceptible to other B-lactam agents they usually respond to amoxycillin treatment for lung infections. Recent New Zealand data indicates that approximately 93% of pneumococci are susceptible to amoxycillin or augmentin.

Sputum cytology

Early morning deep cough specimens should be collected on 3 separate days and each one delivered to the laboratory that day to prevent the cell deterioration that occurs if specimens are stored for more than a few hours. Refrigeration at 4°C slows deterioration. 65% of lung tumours are picked up by three good specimens and 85% by five specimens.

SST (serum separator tube) see Tubes for blood collects

Staphylococci


These organisms are divided into two groups according to whether they produce coagulase, an enzyme-like protein that bestows invasive potential.

Coagulase-positive staphylococci Staph. aureus The common pyogenic organism of skin and wound infections and a variety of serious systemic infections. About 30% of normal people carry Staph. aureus in their anterior nares.

% susceptibilitiesfluclox amox-clav cef cotrim eryth pen

staph. aureus 93¹ 93 93 99 86 9

1. There has been a significant increase in the prevalence of MRSA in Auckland in recent years.2. Quinolones are not recommended for treating S. aureus infection because the MIC's are close to the cutoff for susceptibility and the common emergence of resistance.

MRSA – methicillin resistant Staph. aureus

MRSA are always resistant to methicillin/oxacillin, penicillin, amoxycillin, amoxycillin-clavulanate, and all cephalosporins.

With regard to other sensitivities, it is important to distinguish between two different forms of MRSA:

• multi-resistant MRSA Until 1995 these were the only variety known. They are resistant not only to penicillin and cephalosporins but also alternative oral agents such as erythromycin, tetracycline and cotrimoxazole. They are found infrequently but when identified require action: � isolate the patient � minimise staff contact � screen staff if there is evidence of cross-infection � treat infection


� consider eradication therapy for those who are colonised � consult Infection Control Officer

• non multi-resistant MRSA In 1995 new strains of MRSA were identified

that were seldom resistant to erythromycin, tetracycline or cotrimoxazole. Because they were believed to have originated in Western Samoa, they have been designated WSPP strains and they now represent more than 90% of all MRSA isolates in Auckland. They do not require the expensive infection control procedures listed above but should be treated with standard precautions as for other S. aureus.

MRSA Screening

This is done on patients coming from outside New Zealand for surgery or from parts of New Zealand where there is known to be an MRSA problem.

A minimum of two swabs is required:

• nostrils � one swab inserted into each nostril in turn • perineum � swab close to the groin • skin lesions if present must also be swabbed � these include furuncles, eczema

and psoriasis. The swab should be moistened with transport medium first.

Results are available in 2 or 3 days, depending on speed of growth of the organisms. Where clearance is required for urgent surgery or admission, please provide a phone number.

Coagulase-negative staphylococci Staph. saprophyticus A relatively non-pathogenic organism. It is of clinical interest mainly as a cause of urinary tract infections, particularly in young women where it is second in frequency to E. coli.


% susceptibilitiesamox-clav amox nitrof trim

Staph. saprophyticus 100 98 100 94

Staph. epidermidis A universal skin commensal, non-pathogenic except where host defences are seriously compromised or when introduced by instruments or prostheses.

S. epidermidis is not infrequently grown from an MSU but is of doubtful pathogenicity. If accompanied by pyuria, treatment could be considered bearing in mind the other causes of pyuria.

STD (sexually transmitted disease) The two main pathogens causing urethral or vaginal discharge and pain are Neisseria gonorrhoeae and Chlamydia trachomatis. Collection of specimens is described under Neisseria and Chlamydia. The list of sexually transmitted organisms includes:

• Candida species • Chlamydia trachomatis • Gardnerella vaginalis • hepatitis B • herpes simplex virus • HIV • HPV • Neisseria gonorrhoeae • syphilis (Treponema pallidum) • Trichomonas vaginalis

It is essential that the sexual partner(s) be investigated and treated as well as the person who presents with symptoms.


Steatorrhoea

see Faecal fat Malabsorption

Sterile pyuria see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections): white cells

Steroid estimations

Steroid hormones are described under individual headings including: aldosterone, androstenedione, cortisol, DHEAS, 17-hydroxyprogesterone, oestradiol, progesterone, testosterone.

Stippling of red cells

This classical sign of lead poisoning (qv) is also a non-specific finding in other haemopoietic disorders including aplastic anaemia, thalassaemia, myelodysplasia and megaloblastosis.

Streptococcal antibodies (ASK, ASOT, ADNAse) specimen: serum


ASK = antistreptokinase ASOT = antistreptolysin O titre ADNAse = antiDNAse

ref. ranges:

ASK ASOT ADNAseprobably no infection 0-640 0-250 0-200equivocal 640-2560 250-400 200-350probable recent infection >2560 >400 >350

The figures above are interchangeably described as "titres" or "units".

These tests are used when searching for evidence of recent streptococcal infection in suspected post-streptococcal glomerulonephritis (PSGN) or rheumatic fever (RF).

Serial tests should be done, looking for rising titres. A high level is more likely to be significant and sustained levels may indicate persisting infection. PSGN or RF can easily be over-diagnosed when an isolated, equivocal, titre is used as evidence.

Time-course after streptococcal infection

ASOT and ASK start to rise a few days after infection commences. ADNAse tends to rise somewhat later. In uncomplicated infections, titres return to baseline levels in 2-3 months. Average baseline levels in adults are half those in children due to the frequent streptococcal throat infections in the latter. ASOT does not usually rise in streptococcal skin infections whereas ADNAse does.

see also Rheumatic fever


Streptococci

Streptococci cause a wide spectrum of common diseases. Three species or groups are commonly isolated.

1. Streptococcus pyogenes

Also known as beta-haemolytic group A streptococcus, this organism is the common cause of bacterial pharyngitis. It also causes 20% of skin and wound infections, particularly cellulitis and impetigo where it is the most frequent pathogen. There are a wide variety of other less common sites of infection.

% susceptiblepen amox-clav cef eryth tetra

Strep. pyogenes 100 100 100 99 80

Strep. pyogenes pharyngitis is responsible for the post-strepococcal immune disorders rheumatic fever and post-streptococcal glomerulonephritis hence the importance of recognising and treating the infections, particularly in children.

see also Streptococcal antibodies (ASK, ASOT, ADNAse), Throat swabs.

2. Streptococcus pneumoniae

Often called the pneumococcus, a common commensal in our upper respiratory tract, with up to 60% of people carrying it. It is a gram-positive diplococcous which causes α -haemolysis on blood agar (greening of the agar due to partial haemolysis of the red blood cells) and often has a capsule conferring resistance to host defences. More than 80 different serotypes are known but most disease is caused by a limited number of serotypes. Transmission is from person to person by droplet spread.


It causes a wide range of infections : pneumonia with or without bacteraemia, otitis media, sinusitis , meningitis, and other types of invasive disease. It does not cause pharyngitis or tonsillitis. 30-50% of community acquired pneumonia is due to pneumococci and around 10% of nosocomial pneumonia. There are about 80 cases of pneumococcal bacteraemia a year in Auckland.

Several conditions are associated with more frequent and severe pneumococcal pneumonia: alcoholism, diabetes, chronic renal disease, heart failure and some malignancies.

% susceptibilitiespen eryth tetra cotri chlor

Strep. pneumoniae 71 80 81 52 96

While pneumococci with reduced susceptibility to penicillin are alsoless susceptible to other B-lactam agents they usually respond toamoxycillin treatment for lung infections. Recent New Zealanddata indicate that approximately 93% of pneumococci aresusceptible to amoxycillin.

In the eye, S. pneumoniae is susceptible to chloramphenicol ointment but is intrinsically resistant to neomycin.

Pneumococcal vaccine Splenectomised patients are at significant risk for invasive pneumococcal disease and should receive vaccine. Pneumococcal vaccine contains 23 of the most common serotypes and covers 90% of strains causing invasive diseases. 90% of adults respond to a single dose. The vaccine is also recommended for persons >65 years, persons at increased risk of complications such as those mentioned above, immunocompromised patients, including those with HIV. It is ineffective in children under the age of 2 years. The vaccine is under utilised. Greater use will probably require a change in its funding.


3. Viridans streptococci

Universally present in the throat as a commensal. It can cause sub-acute bacterial endocarditis when it settles on damaged heart valves during transient bacteraemia.

Streptococcus bovis is a member of the viridans streptococci which is important through its association with colonic neoplasia. 20% of patients with S. bovis bacteraemia have an underlying colonic adenocarcinoma and they also need evaluation for endocarditis.

4. Streptococcus faecalis (Group D streptococcus) see Enterococcus

Strongyloidiasis

Intestinal infestation with Strongyloides stercoralis is found world-wide in tropical regions, particularly SE Asia and Central America. Clinically it can present with abdominal discomfort, diarrhoea or malabsorption. A life-threatening disseminated hyperinfection occurs in immunocompromised patients. Diagnosis relies on finding larvae in faeces or, in disseminated disease, respiratory secretions. It tends to be less easy to eradicate than hookworm, which is a related nematode. Treatment of choice is now ivermectin, 200 µg/kg/day once daily for two days. Treatment of infection in immunocompromised patients requires specialist advice. Follow-up tests are recommended 4-6 weeks after treatment.

STS (serological tests for syphilis) see Treponemal serology (STS, serological tests for syphilis)


Subacute thyroiditis see Thyroid disease � diagnosis and monitoring, paragraph D

Sulphaemoglobin see Haemoglobin pigments

Sweat electrolytes

specimens: an appointment is necessary

ref. ranges:

interpretation sweat Na+ or Cl -

normal <40 mmol/L doubtful 40-50 mmol/Lcystic fibrosis >50 mmol/L

In the absence of DNA testing, this is the definitive test for cystic fibrosis (qv). Sodium and chloride levels in the range 80-190 mmol/L are consistent with the diagnosis.

The sweat specimen is collected into a patch of blotting paper taped to an area of skin to which a weak electric current is applied. Sodium and chloride are present in sweat in approximately equal concentrations. The test turns positive in affected infants at age 3-5 weeks.


Synacthen stimulation test

specimens: serum

� collect baseline specimen � inject 0.25 mg Synacthen (synthetic ACTH) IM � collect specimens ½ hr and 1 hr after Synacthen injection. The peak level is

usually reached at 1 hr rather than ½hr. Indications: Used in suspected Addison's disease or for assessment of adrenal reserve after long-term steroid therapy.

Interpretation:

The criterion for adequate adernal reserve or Synacthen testing is a peak level of 700 nmol/L or more. The degree of rise is not useful to confirm or refute an adequatre response.

A basal level >500 nmol/L almost always indicates adequate adrenal reserve unless the patient is on steroid treatement or under severe stress.

In the rare situation where there is pituitary disease of recent onset, the Synacthen test may be normal, becoming abnormal later as the adrenal atrophies.

Synovial aspirate

specimens: collect into a plain tube. If sufficient fluid is available, collect a citrate (blue top) tube as well.

Synovial fluid examination provides definitive diagnosis of septic arthritis, gout and pseudogout, and places other effusions into the broad categories of non-inflammatory


lesions (trauma, osteoarthritis, etc.) and inflammatory non-infective disease (rheumatoid arthritis, etc.).

Examination covers the following:

� gross appearance: clear, cloudy, purulent, blood-stained (trauma) � volume � white cell count - normal <200/cmm non-inflammatory 200-2000/cmm inflammatory non-infective 2000-60,000/cmm septic arthritis >60,000/cmm � white cell differential � polymorphs predominate in septic arthritis, gout, pseudo-

gout and sometimes in rheumatoid arthritis; mononuclear cells usually predominate in the inflammatory non-infective disorders.

• Gram stain � crystals � polarised light is used to look for the urate crystals of gout or the

pyrophosphate crystals of pseudogout. � culture � aerobes, gonococci and anaerobes

Other examinations will be performed on request. Synovial fluid rheumatoid factor is not a useful test.

Syphilis

Syphilis is uncommon in New Zealand and most genital ulcers have other aetiologies. Where there is a possibility of syphilis, serological tests (see Treponemal serology (STS, serological tests for syphilis)) should be performed. If a lesion is strongly


suspicious of syphilis with the typical painless indurated ulcer, direct fluorescent stain can be arranged with the microbiologist.

see also Treponemal serology (STS, serological tests for syphilis)

Systemic lupus erythematosus see SLE (systemic lupus erythematosus)

T

T3, free (tri-iodothyronine) specimen: serum

ref. range:

pmol/L< 10 yrs 3.0 - 10.0> 10 yrs 2.5 - 5.5pregnancy 1st trimester 3.0 - 7.6 2nd 2.8 - 7.2 3rd 2.6 - 6.4


T3 is the active thyroid hormone with T4 being effectively a "prohormone". 80% of T3 is formed from T4 in the tissues, the remainder being directly secreted by the thyroid.

Like T4, T3 is protein-bound in the blood and protein-binding abnormalities can elevate both free and total T3 without causing hyperthyroidism.

Elevated by:

• hyperthyroidism, including T3 thyrotoxicosis • T3 (Tertroxin) therapy � because T3 has a short half-life, levels fluctuate up

to 30% depending on time of last dose. • subacute thyroiditis � early stage

see Thyroid disease � diagnosis and monitoring, paragraph D6 • Hashimoto's thyroiditis � occasionally in early stage see Thyroid disease �

diagnosis and monitoring, paragraph C4 • heterophilic antibodies, protein-binding abnormality

see Thyroid disease � diagnosis and monitoring, paragraph D2 Lowered by:

• hypothyroidism � but is a poor test for this • T4 therapy � though T3 is usually within the reference range when T4 dose

is appropriate • non-thyroidal illness see Thyroid disease � diagnosis and monitoring,

paragraph D1 • drugs : amiodarone (qv), propranolol, steroids, • lithium, iodine in tonics or contrast medium • hypopituitarism (secondary hypothyroidism)

see Thyroid disease � diagnosis and monitoring, for more detail.


T4, free (thyroxine)

specimen: serum

ref. ranges:

pmol/L4 - 7 days 16 - 401 - 4 wks 15 - 351 - 12 mths 11 - 32Over 1 year 10 - 24pregnancy 1st trimester 10 - 23 2nd 10 - 19 3rd 8 - 19

Although T4 is the principal thyroid hormone, it is converted to T3 in the tissues. It is the preferred thyroid replacement therapy in hypothyroidism.

Elevated by:

• hyperthyroidism • T4 (Eltroxin) therapy � because the half-life is long, time of sampling for

monitoring is unimportant. • non-thyroidal illness see Thyroid disease � diagnosis and monitoring,

paragraph D1 • drugs: amiodarone, NSAIDS, propranolol, steroids, iodine-containing contrast

medium, heparin • heterophilic antibodies, protein-binding abnormalities see Thyroid disease �

diagnosis and monitoring, paragraph D2 • sub-acute thyroiditis � early stage see Thyroid disease � diagnosis and

monitoring, paragraph D4 • Hashimoto's thyroiditis � early stage see Thyroid disease � diagnosis and

monitoring, paragraph C4 • self-administration of T4 e.g. for attempted weight reduction Lowered by:


• primary hypothyroidism • non-thyroidal illness (uncommon) • hypopituitarism (secondary hypothyroidism) • Hashimoto's thyroiditis • sub-acute thyroiditis (recovery stage) • drugs: T3 (Tertroxin), phenytoin, lithium, carbamazepine see Thyroid disease � diagnosis and monitoring

Target cells

These are cells with a "target" appearance due to a stained centre within the normal hypochromic zone. They are seen in liver disease, thalassaemia, after splenectomy and in severe iron deficiency.

TB see Tuberculosis (TB)

TCT see Thrombin clotting time (TCT)

TDM (therapeutic drug monitoring) see Drugs, therapeutic monitoring (TDM) (TDM) individual drug listings


Tegretol (carbamazepine) see Anticonvulsants

Telopeptide see N-telopeptide

Testosterone specimen: serum

ref. ranges:

free testosterone total testosteronepmol/L nmol/L

adult female 8 - 58 0.5 - 2.5adult male 380-1200 11.0 - 35.0

Note :

• These are peak values measured at 7-9 am. Late afternoon and evening values can be substantially (20-30%) lower, especially in young men.

• The lower ends of these ranges are not well-defined. A total testosterone of

say 9 or 10 in a male may be transient or may be normal for that person.

• Acute illness lowers testosterone levels which should be measured only in well patients.


Free and total testosterone

Free testosterone, the biologically active fraction, is derived from total testosterone using the value for SHBG which is the serum binding protein. Where the increase in testosterone is small, as in minor degrees of hirsutism in the polycystic ovary syndrome, it may be found that only the free testosterone is above its reference limit.

Age changes in males

The male embryo has high levels of testosterone falling to female levels at time of birth but with a second peak during the first few months of life. Throughout childhood male levels are not much higher than in females until at about age 11 the pubertal rise commences, reaching adult levels at about age 17. Levels decline slowly from about age 40 on, the decline being more marked in free testosterone than total testosterone which is partially sustained by a rise in SHBG.

About 50% of males aged over 60 have free testosterone levels below the young male reference limit. Level of sexual activity and libido are not usually correlated with testosterone levels until total testosterone falls below 8.


Increased levels• hirsutism (50% of cases)• polycystic ovary syndrome• adrenal tumours• drugs

– some testosterone supplements– oestrogens in low dose– anticonvulsants (free level is often low)

• exercise

Decreased levels• obesity• alcoholism• debilitating disease• primary hypogonadism - LH is elevated• secondary hypogonadism - hypopituitarism (qv)• hyperprolactinaemia• hypothyroidism• haemochromatosis• hepatic insufficiency• drugs

– synthetic androgens– steroid therapy– high dose oestrogens– phenothiazines and others– oral contraceptives

Thalassaemias

The thalassaemias are common hereditary conditions in which there is a reduction in the synthesis of one or more of the four globin chains of the haemoglobin molecule. Adult haemoglobin, HbA, which makes up >96% of normal Hb, contains two a and two ß globin subunits and these define the two main groups of disorders, the a thalassaemias and the ß thalassaemias.


The genes for thalassaemia are found commonly in Asians, Polynesians, Africans and Mediterranean peoples. Clinically, the thalassaemias range from the clinically undetectable heterozygous state, through mild microcytic, hypochromic anaemias, (thalassaemia minor) to severe transfusion-dependent anaemias or foetal death (thalassaemia major).

Clinical presentation

The major thalassaemia syndromes usually come under specialist care early in life with moderate or severe haemolytic anaemias.

The thalassaemia trait disorders, which are usually asymptomatic, will for the most part be discovered incidentally on a routine blood film:

� anaemia, usually mild, sometimes moderate, sometimes lower end of the reference range

� microcytic, hypochromic blood film, resembling an iron deficiency anaemia but

with an MCV which is disproportionately low compared with the anaemia � normal ferritin, s. iron, iron-binding capacity � the blood film may show other suspicious abnormalities; and the histogram of

red cell size distribution may show a pattern typical of thalassaemia.

When iron deficiency coexists with thalassaemia, the diagnosis may not become apparent until iron replacement has been achieved.

Diagnosing the type of thalassaemia

The thalassaemias are complex and diverse and under certain circumstances may require specialised DNA and globin chain analyses to characterise them fully. In


ordinary clinical practice, once the diagnosis of thalassaemia has been suspected because of microcytosis in the absence of iron deficiency, a group of tests is applied to broadly separate a from ß thalassaemias. These tests are:

• HbH inclusion bodies (a) • Hb electrophoresis • HbA2 % (ß) • HbF % (ß) • Kleihauer stain (ß)

Alpha Thalassaemias

Each parent contributes two a genes giving a total of four. Alpha thalassaemia results from deletion of 1 or more of these 4 genes.

deletion Hb MCV HbH bodies clinical

-a /aa single gene N N absent 'silent carrier'-a /-a two gene (trans) N N (usually) very occas. Polynesian type

--/aa two gene (cis) ± occas. more severe than trans.Asian type--/-a three gene numerous HbH disease--/-- four gene - - - intrauterine death

Beta thalassaemias

Beta thalassaemias arise from point mutations in the coding genes rather than deletions and more than 300 mutations have been identified. The first thalassaemia to be described, by Cooley in 1925, was severe ß thalassaemia found in a patient of Mediterranean descent, thalassa being the Greek for sea.

a and ß thalassaemias occur with roughly equal frequency.


Clinical implications of thalassaemia

Once a thalassaemia has been identified it is essential that the patient be told of the diagnosis and that they should not be given iron unless there is coexisting iron deficiency.

Testing of a partner and genetic counselling may be required for a woman planning a family.

Theophylline (Nuelin)

specimen: serum

therapeutic range: 55-110 µmol/L

The therapeutic range refers to peak levels. The specimen is collected 4-6 hours after the last dose for long-acting preparations, 2 hrs after those that are short-acting.

Thirst see Polydipsia/polyuria

Threadworms see Enterobius vermicularis (pinworm)


Throat swabs

Swabs are taken from the tonsillar area for a sore throat, or the posterior pharyngeal wall for sinus trouble so as to collect post-nasal discharge.

The most common indication for a throat swab is to detect Group A streptococcus (S. pyogenes). Culture results take 1-2 days to be reported.

Rapid streptococcal antigen tests are not performed in the laboratory. Their general use increases the cost of testing as it is commonly recommended that all patients with a negative rapid antigen test require a culture.

Streptococcus pyogenes (qv), which is 100% sensitive to penicillin, is by far the commonest bacterial pathogen in pharyngitis in immune competent patients. Occasional pathogens include Arcanobacterium haemolyticum (qv), Bordetella, gonococci, groups C and G streptococci, diphtheria, and anaerobic organisms in quinsy.

Thrombin clotting time (TCT) specimen: plasma (citrate)

ref. range: 10-18 seconds

The thrombin clotting time is prolonged by hypofibrinogenaemia, dysfibrinogenaemias, FDPs and heparin.


Thrombocytopenia

A reduction in platelets below 150 x 109/L. The lower the platelet count, the stronger the possibility of spontaneous bleeding.

80-150 bleeding very unlikely 40-80 bleeding unusual 20-40 bleeding becomes increasingly common but is certainly not invariable 0-20 severe thrombocytopenia which can be life-threatening. Should always be referred to a haematologist.

Bleeding is not directly proportional to the degree of thrombocytopenia.

Thrombocytopenia in pregnancy can put the foetus at risk and should be referred for a specialist opinion.

Causes of thrombocytopenia:

· acute infection transient, often marked, thrombocytopenia may be seen in association with acute viral illnesses in children. In this setting, platelet levels often recover rapidly. Post-viral thrombocytopenia in adults may persist at mild to moderate levels and is assumed to have an immune-mediated mechanism. Acute HIV infection may be a cause of thrombocytopenia.

· drugs a long list including salicylates, sulphonamides,

trimethoprim, penicillins, cephalosporins, methyldopa, chlorthiazide, frusemide, tolbutamide, heparin, phenytoin, phenobarbitone, carbamazepine, phenothiazines, phenylbutazone, gold, penicillamine � and others.


· alcohol and liver disease · ITP (qv) idiopathic immune thrombocytopenic purpura · leukaemias · marrow infiltration malignancy, myelofibrosis · other hypersplenism, SLE, B12 or folate deficiency, DIC, post-

transfusion, post-partum · pregnancy ITP, dilutional or gestational thrombocytopenia, GPH

syndromes

Thrombocytosis Refers to an increase in the platelet count above 450 x 109/L.

Transient reactive thrombocytoses up to about 800 x 109/L are common. Causes are:

• blood loss • surgery, trauma • infection, including viral infection • other inflammatory disorders • malignancy � an important cause of persistent thrombocytosis • myeloproliferative disorders • essential thrombocythaemias • polycythaemia vera • myelofibrosis • myelodysplasia


Thromboembolic disease

see Hypercoagulability Venous thromboembolism (VTE) Antiphospholipid antibody syndrome (APS)

Thrombophilia Thrombophilia, an increased tendency to thrombosis, either inherited or acquired or both, is described under hypercoagulability.

Thyroglobulin

specimen: serum


Used for monitoring treatment of thyroid carcinoma

Thyroglobulin antibodies see Thyroid antibodies


Thyroid antibodies

specimen: serum

ref. range: not present

Graves' disease and primary hypothyroidism are both autoimmune diseases and are associated with a variety of antibodies.

Antimicrosomal and anti-thyroglobulin antibodies

These are the standard "thyroid antibodies" requested and they give the same information; when only one is elevated, it is more likely to be anti-microsomal.

Elevated in: · Hashimoto's thyroiditis � antibodies in high titre will differentiate non-toxic

goitre from Hashimoto's · primary hypothyroidism � antibodies present in 90%, often in high titre · thyrotoxicosis � 90% have antibodies, usually in low titre · autoimmune disease marker � there is an association with diabetes and

pernicious anaemia. · euthyroid normals � 10% have antibodies usually in low titre. Annual follow up

will show progression to thyroid disease in some, indicating that these elevations can be a marker for an early autoimmune state.

Thyroid Stimulating antibody (TSab, also called TSH receptor ab)

This IgG antibody, formerly known as LATS, is the marker for autoimmune thyrotoxicosis (Graves' disease).


Thyroid disease — diagnosis and monitoring A. Choice of test TSH is the one-test screen for patients with non-specific symptoms such as

tiredness. A level between 0.4 and 4 mU/L gives 99% exclusion of hyper- or hypothyroidism.

T4 is added:

• when there are more specific symptoms of thyroid disease such as tachycardia, atrial fibrillation, weight loss, cold or heat intolerance etc.

• when monitoring thyroid therapy • suspected hypopituitarism

T3 is added when thyrotoxicosis is suspected. The combination of clinical and laboratory features will indicate probable status

as hyperthyroid, hypothyroid or euthyroid.

B. Hyperthyroid states 1. Aetiology of thyrotoxicosis There are three main causes of thyrotoxicosis:-

• Graves' disease (65%) diffuse hyperplasia associated with autoimmune TSH receptor antibodies and often with ophthalmopathy. Graves' disease is 10x commoner in women and has a peak incidence in middle life. Treatment with carbimazole is associated with remission in 50%.


• Toxic multinodular goitre (25%) � the incidence steadily increases with age. This is not an autoimmune condition and there is no ophthalmopathy. Because remission is infrequent, treatment is typically with I131.

• Toxic uninodular goitre (<10%) � defined by radionuclide scan.

Treatment is by surgery or I131ablation.

2. Lab results in thyrotoxicosis

Thyroid tests The clear-cut case has a T4 above 40, a T3 above 12 and an undetectable TSH (<0.03). Borderline abnormalities in a clinically euthyroid person suggest that hyperthyroidism, if present, is of mild degree. Over a period of time, mild hyperthyroidism can either progress to more obvious disease or revert to normal, hence the importance of monitoring levels at intervals of 1-6 months. T3 thyrotoxicosis (normal or low T4, TSH, <.03, raised T3) will be missed if T3 is not measured in all patients with undetectable TSH, particularly if they are clinically hyperthyroid. T3 thyrotoxicosis is more frequent in the elderly.

Non-thyroid tests Other abnormalities that may be found are: � elevated ALP of bony origin � elevated calcium � elevated ferritin � elevated liver enzymes � normocytic anaemia

� macrocytosis due to associated pernicious anaemia � neutropenia

3. Monitoring carbimazole therapy


Because of the possibility of agranulocytosis, a blood count is part of the pre- and post-treatment laboratory profile along with T4 and TSH. With the usual starting dose of about 15mg carbimazole twice daily, many patients will be clinically and biochemically euthyroid within 4 weeks though biochemical abnormalities may lag behind clinical changes and later overshoot into hypothyroidism. The aim is to adjust the carbimazole dose, usually downwards, and monitor the T4 and TSH at about 8-week intervals so as to keep them normal over a 12-24 month period after which withdrawal can be observed to see if remission has been obtained.

4. Hashimoto's thyroiditis and subacute thyroiditis (see below) can

both pass through transient hyperthyroidism in their early stages. 5. Factitious thyrotoxicosis due to taking of T4 or T3 tablets must

always be kept in mind.

C. Hypothyroid states 1. Primary hypothyroidism

This is an autoimmune disorder, more common in women and with advancing age, reaching a prevalence of around 10% above the age of 60. Because its presenting symptoms resemble those of normal aging, the diagnosis can easily be missed if a screening TSH is omitted. The term subclinical hypothyroidism describes clinically euthyroid patients with a TSH between 5 and 10 and a T4 in the 8-16 range. There is debate whether they need to be treated withthyroxine but early treatment is favoured in the younger age group (40-60 yrs), and those, with high levels of thyroid antibodies or hypercholesterolaemia. If not treated, these patients should be monitored at least annually

2. Lab results in primary hypothyroidism

• Thyroid tests


The diagnosis rests on the elevation of TSH, usually above 20, and often over 100 which makes it one of the easiest diagnoses in laboratory medicine. T4 is variably reduced but may still be within the population reference range. T3 levels are a poor predictor of hypothyroidism.

• Non-thyroid tests Abnormalities that may be found include: � elevated cholesterol � elevated triglyceride � elevated CK due to myopathy � elevated liver enzymes � normocytic or macrocytic anaemia due to direct effect on

erythropoiesis � macrocytosis due to associated pernicious anaemia � iron-deficiency anaemia due to associated menorrhagia � elevated creatinine

3. Thyroxine therapy in hypothyroidism

The aims of therapy are:

• reduce TSH to within the reference range • eliminate symptoms of hypothyroidism • avoid induction of cardiac ischaemia or arrhythmias in those

with coronary artery disease or in the elderly. • reduce cholesterol and triglyceride to their euthyroid levels

The dose range for thyroxine is usually in the range 0.05-0.15 mg/day, depending on body weight. A healthy younger person weighing 70 kg could start at 0.10 mg/day.

After two months to allow hormone levels to reach their new equilibrium (the TSH can be slow to change), T4 and TSH are re-measured. Depending on whether the TSH is above or below the range 0.4-4.0, the thyroxine dose will be increased or decreased by 0.025 mg/day with further laboratory check in two months.


In the older person or those with coronary artery disease, the starting dose is 0.025 mg/day, increasing by 0.025 every 8 weeks until TSH has fallen or cardiac symptoms call a halt to further increases. Thyroxine therapy, once stabilised, will continue for life with monitoring of TSH every 6-12 months or more frequently if the patient's clinical status changes.

4. Hashimoto's thyroiditis Like primary hypothyroidism, this is an auto-immune destruction but instead of gland atrophy there is infiltration with lymphocytes and exudate causing goitre. In theearly stages, release of T4 and T3 into the blood stream can cause mild thyrotoxicosis but this leads to permanent hypothyroidism.

5. Secondary hypothyroidism due to hypopituitarism is very much less

common than other aetiologies but must always be considered in the puzzling situation where T4 and T3 are low and the TSH is normal or low instead of showing the expected elevation. The finding of a normal TSH in these hypothyroid patients is due to detection of physiologically inactive TSH by the assay.

see also Hypopituitarism

6. Congenital hypothyroidism � see neonatal screening

D. Euthyroid states with abnormal thyroid tests

1. Non-thyroidal illness (sick euthyroid syndrome) Any intercurrent illness, particularly when severe, can cause transient depressions in TSH, T3 or T4 levels. Sometimes the T4 is elevated and the TSH may rise briefly during the recovery phase.

2. Thyroid autonomy/subclinical hyperthyroidism with normal T4

and T3 but low TSH

The situtation where a suppressed TSH is found in a healthy, clinically euthyroid patient has a prevalence of up to 15% in older patients. The term thyroid autonomy describes the situation where thyroid hormone secretion is suppressing pituitary TSH partially or


completely but without lifting T4 or T3 levels above their reference ranges and without clinically detectable hyperthyroidism. Euthyroid suppression of TSH is more common in women, in the elderly, and in patients with multi-nodular goitre. Because a small percentage of these patients progress to overt hyperthyroidism, monitoring is indicated, perhaps annually, particularly in those where TSH remains persistently undetectable.\

3. Pregnancy

Because hCG has some thyroid stimulating activity, TSH may be suppressed during the first trimester.

4. Thyroid-binding protein abnormalities and assay artefact

Sometimes T4 and/or T3, and occasionally TSH as well, are markedly elevated (e.g. a T4 of 50-100 pmol/L) in a person who is clinically euthyroid. This is due to presence of clinicallyirrelevant heterophilic or autoantibodies in serum or else to abnormal thyroid-binding serum proteins.

5. Subacute thyroiditis

A not uncommon condition due to viral infection of the gland which is swollen and tender � the thyroid equivalent of mumps. As in Hashimoto's there can be a thyrotoxic picture in the early destructive stage but return to normal is usual, sometimes with a hypothyroid swing during the recovery stage.

Thyroid stimulating hormone (TSH) specimen: serum

ref. range:


mU/L

cord blood 3 - 20age 1 day 10 - 100 2 - 3 days 1 - 20 4 days - 1 yr 1.0 - 8.0children & adults 0.4 - 4.0

TSH is the thyroid screen test of choice � a level between 0.4 and 5 mU/L gives 99% exclusion of hyper- or hypothyroidism.

The third generation assays now in common use measures down to 0.03 mU/L. A level below this, described as an undetectable TSH, is strongly supportive of a diagnosis of thyrotoxicosis.

Abnormal TSH levels, whether high in hypothyroidism or low in hyperthyroidism, respond slowly to appropriate therapy with the new equilibrium level not reached for 2-8 weeks.

TSH is elevated by

• primary hypothyroidism, subclinical or clinical � see Thyroid disease � diagnosis and monitoring paragraph C1

• Hashimoto's thyroiditis � see Thyroid disease � diagnosis and monitoring

paragraph C4 • subacute thyroiditis, recovery phase � see Thyroid disease � diagnosis and

monitoring paragraph D5 • non-thyroidal illness � occasionally during recovery phase � see Thyroid

disease � diagnosis and monitoring paragraph D1 • ectopic TSH from tumours of lung, breast etc. • drugs: lithium, metoclopramide, clomiphene, domperidone, iodides: kelp tabs,

amiodarone, contrast medium


• TSH release is pulsatile � minor elevations may simply be detecting the transient

peak of a pulse. TSH is decreased by:

• hyperthyroidism � usually the TSH is <0.03 in clinical thyrotoxicosis �

see Thyroid disease � diagnosis and monitoring paragraph B2

• thyroid autonomy /sub-clinical hyperthyroidism � see Thyroid disease � diagnosis and monitoring paragraph D2

• patients on supra-optimal T4 or T3 therapy � see Thyroid disease �

diagnosis and monitoring paragraph C3

• drugs: steroids, L-dopa, bromocriptine, heparin.

• non-thyroidal illness � see Thyroid disease � diagnosis and monitoring paragraph D1

see Thyroid disease � diagnosis and monitoring

Thyroiditis, sub-acute see Thyroid disease � diagnosis and monitoring � paragraph D5

Thyrotropin see TSH


Thyrotropin releasing hormone see TRH (thyrotropin releasing hormone) stimulation test

Thyroxine see T4, free (thyroxine)

TIBC (total iron binding capacity) see Iron-binding capacity (IBC) and saturation

Tinea see Dermatophytes

Tobramycin see Aminoglycoside, serum levels

TORCH(es) antibodies


This is an acronym derived from infections causing intra-uterine growth retardation or death : Toxoplasma, Other, Rubella, CMV, Herpes (and Syphilis).

"TORCH antibodies" is no longer regarded as an appropriate block of tests � individual tests should be requested according to indications.

Torulopsis glabrata (Candida glabrata)

A yeast which closely resembles Candida albicans (q.v.) in both symptoms and treatment.

Total CO2 see Bicarbonate

Total protein see Proteins, total, serum

Toxic granulation see Neutrophils (polymorphs), neutrophilia


Toxocara canis (and cati)

An ascarid worm found in dogs and passed on to young children who ingest egg-contaminated dust and soil. Eggs passed in dog faeces are not infective and require 2-5 weeks under favourable conditions to mature. Ingested mature eggs hatch, releasing larvae which traverse gut mucosa and may migrate to any organ, in particular eye and lung. Antibodies to Toxocara are common throughout the world but clinical infections (visceral larva migrans) are rare. Eosinophilia, often marked, may be present. A limited serology study in New Zealand revealed <5% of adults and teenagers were seropositive. Treatment is of unknown value.

Toxoplasma specimen: serum

ref. range : IgM antibodies reported as; negativeborderlinepositive

IgG antibodies 0 - 6 µ/ml -ve >6 µ/ml +ve

IgM antibodies become detectable 5 days after infection and remain for months or occasionally years. A positive IgM result does not separate current from past infection except when a rising titre can be demonstrated. Approximately 2% of women tested antenatally are +ve for IgM but most do not have active infection.

IgG antibodies become positive 1-2 weeks after infection and remain positive for life. A strongly rising titre over a 3-week interval is good evidence of current infection. 30 - 60% of the population have IgG antibodies.

Life-cycle & clinical disease


Toxoplasma gondii is an intracellular protozoan found in cats, humans, sheep, pigs and other mammals. Cats are the primary hosts spreading cysts in their faeces to be accidentally ingested by cat-lovers and grass-eating animals. In the secondary host � man� domestic animals � the infection is usually subclinical but with lymphadenopathy, variant lymphocytes in the blood film and a lymphocytosis. Viable parasites in the tissues of domestic animals cause infection when their meat is eaten undercooked. In the immunocompromised human, quiescent lesions can be reactivated causing serious disseminated infections.

Toxoplasmosis in pregnancy

About one third of women acquiring toxoplasmosis during pregnancy will transmit the parasite to the foetus. In the first trimester the incidence of infection is about 10% but with a high risk of serious or fatal disease in the foetus. In the second and third trimesters the foetal infection rate rises to 30% and 60%, respectively, but with less serious effects in the foetus where the disease may not be apparent until later in childhood with CNS impairment or chorioretinitis.

If antibodies were known to be present at least one month before conception, the foetus will be safe.

Because infection, whether in or out of pregnancy, is usually subclinical, the diagnosis is often made only when an affected foetus or child is encountered.

Sometimes a mother will ask for toxoplasma tests during pregnancy and about 2% of these will test +ve for IgM antibodies, most of them derived from pre-pregnancy infections.

If a mononucleosis-like illness occurs in pregnancy, or if there is any other reason to suspect acute maternal infection, serial testing of antibodies is obligatory followed by toxoplasma DNA testing of amniotic fluid or foetal blood. DNA testing of amniotic fluid at around 18 weeks of pregnancy is highly predictive for the presence or absence of foetal infection. Discussion with a microbiologist is recommended when toxoplasmosis in pregnancy is suspected.


TPHA see Treponemal serology (STS, serological tests for syphilis)

Transferrin specimen: serum


Transferrin is the serum iron-binding transport protein which is measured by "iron-binding capacity" and is described under that heading.

As an approximation, transferrin = IBC ÷ 20.

see Iron-binding capacity (IBC) and saturation

Trephine biopsy

A trephine biopsy of iliac bone is taken by haematologists as part of a bone marrow examination.

Treponemal serology (STS, serological tests for syphilis) specimen: serum


ref. range: non-reactive

1. Screen test

The initial enzyme-immunoassay test is a screen for both non-treponemaland treponemal antibodies. A positive screen test will be followed by the RPR (rapid plasma reagin), TPHA (treponema pallidum haemagglutination) and FTA (fluorescent treponemal antibody).

2. Non-treponemal (reagin) tests, RPR and VDRL

The RPR and VDRL (venereal disease research lab) are the most widely used of the older, non-specific reagin tests. They can be transiently positive in a wide range of viral and autoimmune diseases as well as syphilis and yaws. After successful treatment of syphilis, the RPR/VDRL titre declines and may become negative. The RPR/VDRL is used as a screening test for syphilis and for monitoring response to treatment. A positive result may be due to:

� current infection � rare in New Zealand. The titre will nearly always be

>1:16 � past, inactive, treponemal infection � the titre is usually <1:16, often 1:1 or

1:2. � SLE � the "biological false positive RPR" is found in 10-20% of SLE and

is one of the serological markers � other autoimmune diseases, including antiphospholipid syndrome � viral infections, malaria and Mycoplasma pneumonia infections � positive

for < 6 months � parenteral drugs � aging


� pregnancy is sometimes listed as an infrequent cause of a low titre false positive RPR

3. Treponemal tests TPHA and FTA

The TPHA and FTA are much more specific for treponemal infections but unexplained, weakly reactive, false positives of one or both tests are sometimes found.

After a treponemal infection, the TPHA and FTA stay positive indefinitely without indicating whether disease is current or past.

In true treponemal infections, all three tests, VDRL or RPR, TPHA and FTA, will usually be clearly reactive. Antibody tests cannot distinguish between yaws and syphilis infections which are both due to Treponema pallidum species. WHO attempted to eradicate yaws from the Pacific Islands in 1961 but without success, there having been numerous new outbreaks since then.

TRH (thyrotropin releasing hormone) stimulation test

Formerly used as a test for borderline hyperthyroidism but now replaced by sensitive TSH estimation. In hyperthyroidism, the TSH response to TRH is reduced.

Trichinosis

An intestinal and muscular infection caused by the nematode Trichinella spiralis. Pigs are the main reservoir, and eating under-cooked pork the principal mode of infection. Although T. spiralis is common world wide, particularly in North America and Europe, cases in New Zealand are most likely to be in persons who have acquired


the disease overseas. New Zealand and Australia are considered essentially free of infection though a focus was detected in a pig farm in the North Island in May 1997. Infected pigs probably still exist. It is likely that rats and wild cats serve as a reservoir.

Diagnostic tests include eosinophil count, CK, serological tests and muscle biopsy.

Trichophyton see Dermatophytes

Tricyclic antidepressants see Antidepressant drugs, tricyclic

Triglyceride specimen: serum

ref. range: <2.0 mmol/L (fasting)

Non-fasting specimens: After eating, dietary triglyceride is found in chylomicrons and smaller "remnant" products. However, 90% of normal people have a non-fasting triglyceride of <1.8 mmol/L which excludes hypertriglyceridaemia and can make the inconvenience of fasting unnecessary.

Fasting specimens (>8 hours after food): The above comment not withstanding, it is usual to measure triglyceride in the fasting state and with abstention from alcohol for the previous 24 hours.


Triglyceride in the fasting state comes from the liver in VLDL particles and their smaller IDL products. When triglyceride metabolism is markedly impaired, chylomicrons can be present in the fasting state. If the fasting triglyceride is above 5 mmol/L, the specimen will appear cloudy due to raised VLDL and/or chylomicrons which rise to form a creamy layer on standing.

Elevated fasting triglyceride:

1. Primary � familial combined hyperlipidaemia � familial hypertriglyceridaemia � type III ("remnant removal disease") hyperlipoproteinaemia 2. Secondary � obesity � alcohol � diabetes � hypothyroidism � liver disease, particularly obstructive � nephrotic syndrome � pancreatitis � pregnancy � significant illness � drugs: oestrogen, oral contraceptives, beta blockers, corticosteroids,

thiazides, retinoic acid, anti-viral agents, valproic acid Very high triglycerides

A patient with a triglyceride above 10.0 mmol/L is at risk for acute pancreatitis and requires immediate restriction of dietary fat and alcohol, treatment of any other underlying cause such as diabetes, and addition of a triglyceride-lowering drug such as a fibrate if other measures fail.

With massive hypertriglyceridaemias, serum can have the appearance and consistency of cream. Often there is more than one aetiology, e.g. diabetes and alcohol.


Triglyceride levels can rise and fall very quickly. Above a level of 6.0 mmol/L, lipoprotein lipase clearance mechanisms are saturated which means that dietary fat can rapidly raise triglyceride to surprising levels. Dietary restrictions may cause it to fall equally quickly.

see also Lipid disorders

Tri-iodothyronine see T3, free (tri-iodothyronine)

Trophoblastic disease see hCG (human chorionic gonadotrophin)

Troponin I (TnI) and Troponin T (TnT)

specimen: serum ref. ranges: Troponin I <2.0 µg/L Troponin T <0.1 µg/L

Elevation of one of the cardiac troponins, which are almost identical in their clinical usage, is more sensitive and specific for myocardial infarction than CKMB. Concentrations rise within 4 - 12 hours of commencement of cardiac pain and remain elevated for 7 days in the case of TnI or 10 days for TnT.


Unstable angina can also cause elevations due to minimal myocardial damage not detected by CKMB. It is important to recognise that angina without myocardial necrosis will not elevate troponins.

If the specimen was obtained less than 12 hours after commencement of chest pain, a follow up should be collected 6-12 hours after the first.

TnT can be elevated in chronic renal failure in the absence of known myocardial damage whereas TnI is largely unaffected.

Absence of rise doesn't exclude ischaemic cause for chest pain � may warrant specialist follow-up.

see also Myocardial markers for infarction (MI) and ischaemia

Trypsin, blood

see Cystic fibrosis Neonatal screening

Trypsin, faeces An old and unsatisfactory test for cystic fibrosis in infants, now replaced by the blood test

see Cystic fibrosis Neonatal screening

Faecal chymotrypsin is sometimes used as a test of pancreatic function.


Tryptase specimen: serum


Tryptase, an enzyme found in mast cells, is released after an anaphylactic reaction, reaching a peak after 1 hour and falling back to baseline over the next 8 hours. It can be used to differentiate true anaphylaxis from non-immunological reactions such as a vaso-vagal attack.

Tryptase may also be used in the diagnosis of mastocytosis.

TSH see Thyroid stimulating hormone (TSH)

Tuberculin test (Mantoux test)

Indications • patients with a clinical illness consistent with TB • people who have been in contact with a case of proven TB. • assessing immune status in a person expecting to work in contact with TB,

e.g. a hospital service dealing with TB or someone working in a country where TB is endemic.

Method


The standard Mantoux test consists of an intradermal injection of 5 units of tuberculin (PPD - purified protein derivative) contained in 0.1 ml of solution. The injection is made into the anterior aspect of the forearm and read 3 days later (2-4 days are the outer limits if 3 days is impracticable).

When reading the test, the arm is palpated to define an area of induration and the diameter of this induration, if present, is measured in mm transverse to the long axis of the forearm.

An area of surrounding erythema (redness), or erythema alone, is ignored.

If vesiculation (blistering) or necrosis (darkening or ulceration) of the indurated skin is present, these must be described as an important part of the result.

Interpreting results

A diameter of induration >10 mm is described as positive and is consistent with current or past TB infection.

A strong positive in a person with active TB disease may be >15 mm with vesiculation and necrosis.

Previous BCG vaccination is associated with induration up to 15 mm though usually <5mm.

In children under age 5 years, an induration >5 mm is read as positive.

In immuno-compromised persons, the tuberculin reaction may be reduced or suppressed, even in the presence of proven infection.


False positive Mantoux results These are usually due to operator error, particularly reading errors where the area of erythema rather than induration has been read.

False negative Mantoux results Although a -ve Mantoux usually indicates that person has never been exposed to TB, there are important exceptions.

• the person has had TB in the past but the immune response has faded. • overwhelming infection or illness of any type, including overwhelming TB. • patients with immune suppression � HIV, immunosuppressive drugs,

sarcoidosis, renal failure, malignancy, malnutrition. • acute viral infections, recent live virus vaccinations. • neonates. • operator error, improperly stored PPD.

Positive predictive value of tuberculin testing The positive predictive value is the % of people with a positive tuberculin reaction who are actually infected with TB.

Figures are not available for New Zealand, but the Canadian figures below are indicative. They are for young adults vaccinated with BCG after age 5.


Positiveprevalence predictive value

(%) (%)

Mantoux result >5 mm >10 mm >5 mm >10 mm

Clinical situationScreening, Canadian born 6 4 17 17Casual contact of smear-positive case 10 10 26 31Household contact of smear-positive case 50 50 63 70Recent immigrant from tuberculosis endemic country 80 70 73 78

Note that despite BCG vaccination, only 6% of Canadian-born subjects had a Mantoux >5 mm. Of these, 17% had TB.

The test has much stronger predictive power in recent immigrants from a TB endemic country. In these, the prevalence of past or present TB infection was 50-60%.

see also MOH Guidelines for Tuberculosis Control in New Zealand, 1996.

Tuberculosis (TB)

One third of the world's population is infected with TB, the majority of them in the developing world.

High risk groups are those who have arrived from Asia or the Pacific Islands in the past few years and those with other family members who have been infected.

Infection is by inhalation of droplet nuclei. Local replication leads to acute disease in about 5% of those infected. It is higher in infants and those more than 60 years old. About 10% of infected people reactivate during their lifetime. This is more common over the age of 50 and in men than women.


Diagnosis

Specific diagnosis requires isolation of bacilli from an appropriate specimen. The tuberculin test (qv) can be useful provided its limitations are recognised.

Specimens

Urines The whole of an early morning specimen should be collected on 3 different days. A special collection jar is provided and each should be returned to the lab on the day of collection.

Sputum ZN stain and culture of sputum is the most effective test for diagnosing

infectious TB. Three specimens should be examined, preferably early morning on separate days. Automated liquid-based culture methods grow TB from most smear-positive specimens within a week.

Bronchial washings Collect into a sterile container Aspirated fluid Collect into a citrate bottle Tissue Specimens for culture must be placed in sterile saline or water,

not in formalin. Treatment

M. tuberculosis remains the predominant cause of mycobacterial disease in New Zealand. The incidence is highest in SE Asian immigrants, Polynesian Pacific Islanders and Maori. Resistance to antituberculous antibiotics is uncommon but highest in immigrants. When tuberculosis is suspected seek specialist advice.


Principal drugs

� Isoniazid (INH) is an oral agent coming in 100mg tablets. Side effects include hepatoxicity and peripheral neuropathy (prevented by routinely taking pyridoxine 10mg daily). The usual dose is 300 mg/day for adults.

� Rifampicin is also an oral agent but there is an IV preparation. It causes red

or orange discolouration of all body secretions (urine, tears, saliva) and may stain soft contact lenses. Fever, rash and hepatotoxicity are other side effects. Usual dose is 600mg daily, commonly combined with INH 300mg daily (Rifanah '300' or '150' tablets).

� Pyrazinamide is now the most commonly used third initial drug. Tablets are

500 mg and common doses are 1500mg - 2000mg. Hepatotoxicity, gastrointestinal tract disturbance and skin rash are seen.

� Ethambutol was the most usual oral third drug but has now been relegated.

Usual dosing is 15 mg/kg/day and tablets are 400mg and 100mg. At higher doses it causes retrobulbar neuritis.

� other agents, e.g. amikacin, ethionamide, new macrolides, new quinolones

and capreomycin may be used for drug resistant tuberculosis.

see also Tuberculin test (Mantoux test)

Tubes for blood collects

Blood consists of two fractions:

• cells � red cells, white cells and platelets • plasma � fibrinogen plus serum


If blood is left to stand in a plain glass or SST tube, the fibrinogen precipitates forming clot which contracts leaving the straw-coloured serum to be poured off the clot.

Haematologists, when doing blood counts, are interested in the cellular components and therefore add an anticoagulant, usually EDTA, to prevent clotting.

Biochemists and immunologists are interested in serum components and use clotted specimens. Sometimes, however, plasma is the preferred specimen rather than serum and a heparin anticoagulant is used.

A further point is that blood cells are a living tissue and continue to live in the tube. As the specimen stands at room temperature, red cells consume energy, converting glucose to lactic acid thus reducing the blood glucose. These processes are slowed but not prevented, by storage in a refrigerator. After a few hours, the red cells become increasingly sick, releasing their potassium, haemoglobin, phosphate and enzymes into the surrounding serum or plasma.

Types of tube

The colour of the stopper denotes the preservative or anticoagulant within the vacutainer. Recently the trend has been to smaller volumes (10 or 7ml tubes changing to 5ml) and from glass tubes with rubber stoppers to all-plastic. As analytical systems evolve, the tubes change but currently, the tubes in use are:

Plain tube bright red plastic top

Provides a clotted specimen from which serum can be poured. Used mainly for immunology tests where antibodies are to be measured. It can be used for biochemistry tests but the SST is preferred because of its superior qualities of separation.


SST tube yellow plastic top Used for most biochemistry tests. SST stands for Serum Separator Tube. It contains a 1cm glug of material which promotes clotting and separation of serum from clot.

EDTA tube purple top

Used for most haematology including haemoglobin, white count, differential, platelets, film and ESR. Also for HbA1c, blood lead and other biochemical tests where the analyte is inside the red cell. EDTA is an anticoagulant which acts by removing calcium.

Citrate tube blue top (also called sodium citrate or buffered citrate) Used for INRs and other coagulation tests. The tube must be allowed to fill completely to achieve optimum citrate:blood ratio.

Fluoride tube grey top

Used only for glucose. The SST or plain tube can be used for glucose provided the specimen is analysed within 2 or at the most 4, hours. Fluoride is an enzyme poison which blocks red cell metabolism and thus prevents the consumption of glucose.

Heparin tube green top

Used for blood gases and some hormone assays.

CPD tube yellow top

Used for tissue-typing, DNA and cell marker studies.


CPD is citrate phosphate dextrose.

Tumour markers

Because of their low specificity, most tumour markers are not used as screening tests � there are just too many false positives.

Their main use is in monitoring treatment and progress in established disease but they are also used when a particular malignancy is suspected on clinical grounds or when the site of the primary lesion is unknown in disseminated malignancy.

marker most common tumour type AFP (alpha foeto protein) primary liver, gonad Bence Jones Protein in urine myeloma CA 15-3 breast CA 19-9 pancreas CA 72-4 gastrointestinal malignancies CA 125 ovary calcitonin medullary thyroid carcinoma catecholamines phaeochromocytoma CEA (carcino-embryonic antigen) colon (various) hCG (human chorionic gonadotropin) testis, placenta HIAA carcinoid tumour immunoglobulins in serum EPP myeloma, macroglobulinaemia PSA (prostate specific antigen) prostate thyroglobulin thyroid carcinoma


Turner's syndrome In Turner's syndrome, phenotypic females have only one X chromosome rather than the usual two. Clinical features include short stature, sexual infantilism and primary amenorrhoea. Gonadal dysgenesis is indicated by raised FSH and LH and low oestradiol.

Diagnosis is based on demonstration of the abnormal karyotype by the cytogenetics laboratory.

Typhoid see Salmonella antibodies (Widal Test) typhi

U

Ulcer scrapings for cytology

These are collected particularly from lesions in the oral cavity suspected of malignancy. Scrape the surface firmly with a wooden spatula or cytobrush. Fix at least one slide with Cytofix as for a cervical smear. Another slide should be left to air-dry if lymphoid neoplasia is suspected.


Unconjugated bilirubin see Bilirubin, conjugated (direct) and unconjugated (indirect) fractions

Units see SI (systeme internationale) units

Urate, serum specimen: serum

ref. range: adult female 0.14 - 0.36 mmol/Ladult male 0.20 - 0.42 mmol/Lchildren 0.10 - 0-.30 mmol/L

0.42 mmol/L has been chosen as the upper end of the male range because this is the level above which the risk of gout begins to rise from 1 in 1000 below 0.42 to 1in 20 at a level above 0.54. About 20% of Auckland males have a urate above 0.42.

0.36 mmol/L is used for women because on average their levels, before the menopause, are 0.06 mmol/L lower than men. After menopause, levels in women approach those in men and their risk of gout increases.

Polynesians have higher levels than Caucasians.


Urate is a breakdown product of cell nuclei, one third from the diet, two thirds from endogenous tissue catabolism. 20% of urate is excreted by the kidney, the remainder in the gut.

Elevated urate Like cholesterol, baseline serum urate levels are genetically determined but elevated by secondary factors:

• high purine diet � liver, kidney, shellfish, fish roe, kina • alcohol • renal insufficiency • drugs : diuretics, salicylates in low dose, steroids, chemotherapeutic agents,

niacin, ethambutol, pyrazinamide • polycythaemia vera • malignancies, particularly leukaemias or lymphomas being lysed by

chemotherapy • hypothyroidism • rare enzyme defects � can present as gout or urate nephropathy in children,

young adults or pre-menopausal women • Down�s syndrome • metabolic syndrome � hypertension, dyslipidaemia, diabetes, obesity • pregnancy � compared with the non-pregnant base-line, levels are 20% lower

1st trimester and 20% higher in the 3rd. Levels above 0.35 mmol/L in the 3rd trimester associated with hypertension are a perinatal risk factor.

• gout � an acute inflammatory arthritis precipitated by urate deposition in synovial tissue and occurring mainly in middle-aged and older men and in post-menopausal women. Demonstration of urate crystals in aspirated synovial fluid establishes the diagnosis beyond doubt. Raised serum urate levels are contributory but not diagnostic. During an acute attack of gout, serum urate may actually fall below the levels that will be found between attacks.


Urate, urine

specimen: 24-hr urine without preservative

ref. range: 1.5-4.5 mmol/day when on average diet

Increased levels are due to high purine diet or endogenous over-production of urate.

Low levels can be due to reduced renal excretion of urate.

Urea

specimen: serum ref. range: < 4 yrs 1.4 � 5.4 mmol/L > 4 yrs 2.6 � 7.7 mmol/L Elevated by:

renal impairment but s. creatinine is a better test being less subject to other interferences

high protein diet an important determinant catabolic states any acute serious illness, particularly sepsis dehydration at low urine flow, there is increased tubular

reabsorption of urea


bleeding into GI tract can give elevations up to 15 mmol/L prostatic hypertrophy or other post-renal obstruction drugs steroids, diuretics As a routine measure of renal function, creatinine has almost entirely replaced urea. Nephrologists, however, measure urea as well as creatinine in dialysis patients, the preferred urea level being below 20-30 mmol/L.

An unexpected fall can be due to loss of albumin in dialysis fluid.

Unexpected rises in dialysis patients can be due to:

� dietary non-compliance, too much protein

� sepsis

� dehydration or catabolic illness

� steroid dose too high

Urethral swabs

Male Where there is a discharge, swabs for Chlamydia (qv) and gonococci (qv) should be collected by the doctor at the time of examination. Alternatively, a specimen can be collected by a male nurse or microbiologist at the laboratory � or, as a last resort, the patient can be given swabs in one of our other rooms and asked to collect the specimen himself. Our female nurses do not collect urethral specimens from males.


In the absence of a discharge, urethral swabs are unlikely to grow a pathogen. A first catch (not mid-stream) urine specimen is a better test for Chlamydia than a swab, particularly when there is no discharge.

Female The urethra should be swabbed for gonococci and Chlamydia when looking for STD.

Uric acid see Urate, serum

Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections)

specimens: MSU (mid-stream urine), CSU (catheter-stream urine) or casual.

Store specimen in fridge while awaiting transport.

Urinary catheter tips are not suitable for culture because results do not predict the presence of bacteruria. They should not be sent.

A. Component tests � bacterial count � culture � Microscopy � performed when an abnormality is detected by dipstick or

when specifically requested (e.g. when searching for casts in suspected renal disease). We use phase contrast microscopy and look for


squamous epithelial cells, white cells, red cells and red cell ghosts, bacteria, casts and crystals.

� dipstick analysis � protein � red cells/Hb � white cells as shown by leucocyte esterase activity � gram-negative infection as shown by nitrite activity which has excellent specificity but only 40-80% sensitivity for infection � glucose � ketones � bilirubin/urobilinogen

B. Interpretation 1. Bacterial count A count of >105/ml (>108/L) in the presence of a

growth of a single organism is virtually pathognomonic of urinary tract infection.

A count of <102/ml is most unlikely to be associated with infection.

This leaves the range 102-105/ml as a grey area where interpretation requires consideration of the whole clinical picture including symptoms, past history, age and sex. For example a sexually active young woman with dysuria and frequency should usually be treated in the presence of pyuria, even if her bacterial count is only 103/ml.

2. Culture A pure culture of a single organism usually indicates

infection whereas a mixed growth is usually due to contaminants. The rule is by no means invariable and in a person with recurrent infections and predisposing factors, a mixed growth may be significant.


Organism % susceptible(% of total isolated) amox-clav amox trimeth cefaclor nitrof norfloxE. coli (74) 95 44 78 98 99 100Proteus mirabilis (5) 97 81 84 97 res 99Staph. saprophyticus (4) 99 65 92 98 100 99Strep. Gp B (4) 100 100 100 99 100 98Enterococci (4) 100 99 53 res 98 79Pseudomonas (3) res res res res res 88Kleb. pneumoniae (3) 96 0 87 97 89 98Staph. epidermidis (1) 97 29 71 85 97 91Staph. aureus (1) 99 17 96 97 100 95% Sens. for all organisms 93 48 75 90 92 98

3. White cells A count of up to 10 white cells/cmm is accepted as normal.

The commonest cause of pyuria (increased white cells) is bacterial infection which will show up in the bacterial count and culture. The infection can be at any level in the urinary tract � urethra, prostate, bladder, kidney.

Sterile pyuria describes the finding of increased white cells but with no bacterial growth on routine media. Causes include:

� resolving urinary tract infection on antibiotics � a test for anti-bacterial

substances (ABS) will be positive. � gonococcal urethritis � standard urine culture media do not grow

gonococci which require a urethral swab for STD � chlamydial urethritis � see Chlamydia trachomatis � renal TB � uncommon but important; consider TB culture � urinary tract tumour � urine cytology may help � calculi � trauma, including recent instrumentation


� prostatitis � viral or Mycoplasma infection � age: elderly men and women may have pyuria, 20-40 WBC/cmm, and

sterile urine Collection of a mid-stream specimen helps to identify urethritis and prostatitis where the white cells are concentrated in a first-catch specimen.

4. Haematuria — red cells and/or free Hb have been detected in the urine.

Normal urine has less than 10 x 106 red cells/L which is approximately at the limit of detection of a urine dipstick.

Dipsticks give a positive test for blood with:

� intact red cells � free Hb � myoglobin

When the dipstick is positive for blood we do a red cell count using phase contrast microscopy. There are 8 possible results : nil, 10, 25, 50, 100, 250, 500, >500. At about the 500 level, blood just becomes visible to the naked eye. Results below this, detectable only by dipstick or microscope, are termed microhaematuria. 40% of our routine urinalyses test positive for blood. Most of these are microhaematuria and most are transient and benign. Sometimes the dipstick is positive but the red cell count nil. On very rare occasions this is due to haemoglobinuria (qv) or myoglobinuria but for practical purposes it can be treated as if it were microhaematuria with red cells present.

When considering diagnostic implications, haematurias can be divided into two groups;

a. Benign or relatively benign transient haematuria

These include the haematurias that have an identifiable benign cause, e.g. UTI and which disappear with elimination of the cause.


� UTI � a very common cause of haematuria. White cells are almost invariably present as well.

� menstrual contamination � also very common. Presence of epithelial

cells indicates contamination � vigorous exercise � benign renal microhaematuria � a somewhat nebulous entity, diagnosed

by exclusion. There is no hypertension or proteinuria and serum creatinine is normal. Phase contrast microscopy of freshurine shows that the red cells are entirely dysmorphic (see below) indicating their glomerular origin.

� contaminants such as hypochlorite � medications, e.g. vitamin C, anticoagulants � transient haematuria of unknown origin � the blood has vanished when a

follow-up specimen is examined. This group includes the unexplained transient dip-stick-only haematuria with no red cells seen on microscopy.

b. Persistent pathological haematurias

A persistant haematuria always requires investigation. Causes include: � urinary tract tumours � urinary tract stones � urinary tract trauma � renal pathology � glomerulopathy, etc. � bleeding disorders � intravascular haemolysis causing haemoglobinuria � myoglobinuria

c. Red cell morphology in haematuria

Some workers recommend examination of a fresh urine (less than 1 hour old) under phase-contrast microscopy to allow distinction of dysmorphic (distorted) red cells, which are entirely of glomerular origin, from eumorphic (normal-looking) red cells which can originate anywhere in the urinary tract. Presence


of eumorphic red cells in urine is an indication to consider further investigation such as cystoscopy and imaging. If the red cells are entirely dysmorphic and there is no clinical or other evidence of renal disease, the diagnosis of benign renal microhaematuria can be applied and follow-up confined to repeat urine in 3-12 months.

5. Proteins The dipstick, which is only semi-quantitative, turns positive at a protein concentration of about 100-300 mg/L. A trace or 1+ can be due to an infection, particularly one involving the kidney rather than just the bladder. A test registering 2+ or greater raises the possibility of glomerular disease. If proteinuria persists, 24-hour urine protein output should be measured.

The dipstick detects mainly albumin and may entirely miss other proteins such as free light chains.

see Proteins, urine (proteinuria) for more detail

6. Casts Hyaline protein casts are found relatively frequently and are not regarded as significant. Granular (white cell) and red cell casts on the other hand are strong indicators for renal disease, particularly glomerular disease.

7. Glucose Positives indicate diabetes or renal glycosuria (qv) and require blood

glucose estimations as follow-up. 8. Bilirubin & urobilinogen Positives require serum bilirubin and liver

enzymes for interpretation.If the blood tests are normal, a positive urobilinogen can be ignored.

9. Crystals Cystinuria is sometimes detected by finding cystine crystals.

Urine cytology

A series of three mid-morning, randomly-voided urine samples from a well-hydrated ambulant patient gives the best results. A 2-3 hour output, (at least 50mls), is required. Urine specimens should be forwarded to the laboratory as quickly as possible and refrigerated (not frozen) if there is any delay. Adequate diagnostic results can be achieved with samples kept cool for up to 48 hours prior to processing


but the best yields require refrigeration of under 4 hours. Catheter specimens, bladder wash, and ureteric specimens are treated similarly.

Urine free cortisol see Cortisol, urine free

Urine, pigmented

Causes include:

Red urine

• haematuria

• phenolphthalein � containing purgatives, which are red when alkaline. Fresh urine is acid but turns alkaline on standing

• diet � beetroot, rhubarb turn red on standing, particularly with coexisting iron deficiency

• some porphyrias � turn red/brown on standing

• haemoglobinuria (qv)

• myoglobinuria (qv)

Orange/brown urine

Concentrated urine in febrile states is sometimes described as abnormal by patients.


• bilirubin, or urobilinogen which turns brown on standing

• drugs, e.g. methyldopa, de Witts pills, chloroquine, rifampicin, quinine, metronidazole, nitrofurantoin, riboflavin

• some porphyrias turn brown on standing

• melanin in disseminated melanoma

• alkaptonuria, turns brown on standing

• tyrosinaemia

Yellow urine

• vitamin B complex, multivitamins

Blue/green urine

• drugs, e.g. amitriptyline, NSAIDs, triamterene

• biliverdin

Milky urine

• infection

• chyluria (qv)


• oxaluria

Factitious additives (something the patient has added) are another source of pigmentation.


Urine, preservatives

Urine specimens should always be kept in the refrigerator to prevent growth of bacteria.

Some tests require special preservatives, the commonest being 10mls of concentrated acid. It is absolutely essential that the patient be warned that any apparently innoccuous-looking fluid in the bottom of the bottle may be dangerous and corrosive. The fluid must not be touched and children must not be allowed to get near the bottle.

Tests which require acid preservatives are:

Catecholamines (for phaeochromocytoma)

HMMA (VMA)

5HIAA (for carcinoid syndrome)

arsenic

copper

lead

No preservative is required for:

creatinine (and creatinine clearance)

free cortisol

protein

cystine

amylase


Urine for TB specimen: 3 early morning urines

see Tuberculosis (TB)

Urobilinogen in urine Urobilinogen is sometimes reported positive on routine urinalysis by dipstick. Viral hepatitis and haemolytic disease should be excluded by checking liver enzymes, reticulocyte count and haptoglobins. If these are normal, the positive urobilinogen can be ignored.

Uroporphyrins see Porphyrias

URTI (upper respiratory tract infection) see Throat swabs

Ear swabs & infections

UTI (urinary tract infection) see Urinalysis (routine biochemistry and microbiology) and UTIs (urinary tract infections)


V

Vaginal discharge specimen: routine swab collected from 5 cm inside the vagina and placed in

transport medium.

The normal flora of the vagina is an abundant growth of gram-positive lactobacilli.

Undesirable organisms are of three main types:

Trichomonas detected by microscopic examination of a smear taken from the swab.

Candida often obvious clinically as a curd-like growth, it is easily cultured.

Bacterial vaginosis a growth of predominantly anaerobic organisms associated with a lack of normal lactobacilli. Clue cells are a feature and Gardnerella vaginalis may bepresent.

Metronidazole provides effective treatment for both bacterial vaginosis and Trichomonas infections.


Where an STD is suspected as cause of a discharge, cervical and urethral swabs should be collected. Vaginal swabs seldom grow gonococci or test positive for Chlamydia.

Valproic acid (Epilim)

specimen: serum

Serum levels are generally unhelpful and should not be done except to check compliance. There is no accepted therapeutic range though levels below 300 µg/L are said to be more likely to be associated with poor seizure control and levels above 700 more likely to be associated with hepatotoxicity.

Vanillyl mandelic acid (VMA) see HMMA (hydroxy methyl mandelic acid)

Variant lymphocytes see Lymphocytes

Variation = variance


When a test is repeated day after day on the same person, results will not be identical. The term variation or variance describes the extent of these day-to-day and week-to-week changes. Consideration of variation is essential when trying to decide whether a patient is getting better or worse. For example, someone's cholesterol is 6.8. They go on a diet. A month later the result is 7.2. Does this mean the diet is making the situation worse?

There are two components to variation.

Analytical variation This is the "noise" in a method, the sum of the technical imperfections that prevent it producing a perfect result every time. Modern methods are vastly better than those in use 20, or even 10, years ago and analytical variation is generally overshadowed by biological variation.

Biological variation

Serum concentrations in the body are controlled by physiological mechanisms which are, not surprisingly, never perfect. This biological variation is typically about twice as large numerically as analytical variation though this varies from test to test.

Here are some indicative examples of biological variation for results within the reference range:

• sodium ± 4 mmol/L

• cholesterol will vary about ± 0.5 mmol over a period of weeks.

• iron commonly is 30% lower in the afternoon than the morning.

• albumin varies 10% according to position (recumbent or

upright), time of day, state of hydration. Medication, such as a morning diuretic, will add further variation.


Concentrations of protein-bound constituents will vary along with the changes in protein level.

• TSH release of this and many other hormones is pulsatile

and the level will vary according to whether the sample is collected at the peak of a pulse or near the trough. TSH, with a reference range of 0.4-4.0 units, can vary by up to 2 units. A change from 0.4 to 2.0 units may not be significant.

It should be noted that reference ranges are made wide enough to allow for variation and that is one reason they are such crude indicators of what is "normal".

Coefficient of variation (CV) The CV is the commonly used method for expressing the analytical or biological variation of a test.

For a good method, e.g. sodium, the analytical CV might be 1-2% and the biological variation 2-4%. Mathematically this gives a combined variation of 2.2-4.5%.

The mathematical application of a measured CV tends to give a wider variation than most people expect. As an example, consider a serum sample with an actual Ca++ level of 2.40 mmol/L. The analytical CV is 2%.

If the serum is tested 100 times, 95% of the analyses will lie in the range

2.40 ± 2cv

= 2.40 ± 2x2%

= 2.40 ± 4%

= 2.40 ± 0.10 mmol/L

= 2.30 � 2.50 mmol/L

%xmean

deviationdardtansCV 100=


In practice, few clinicians actually use these figures. Most assess a result intuitively using a mixture of experience, clinical assessment and theoretical knowledge to decide on the significance of a result and what action to take.

Varicella-zoster virus (VZV)

specimen: air-dried smear from base of fresh vesicle

The same virus is responsible for both chicken-pox (varicella) and shingles (herpes zoster) the latter being a reactivation of dormant virus acquired during a childhood attack of chickenpox.

Diagnosis is clinically obvious in most cases but the virus can be identified by a fluorescent antibody applied to a suitable smear.

To collect the specimen, open a fresh vesicle, scrape the base with a spatula, smear on a slide, air-dry and send to the lab in a labelled envelope.

Although varicella-zoster takes several weeks to grow, culture can be attempted. Use the special viral transport swab (Virocult).

Antibody tests, preferably applied to paired sera, are also available.

VDRL see Treponemal serology (STS, serological tests for syphilis)


Venom see Bee and wasp venom allergy

Venous thromboembolism (VTE)

In hospital practice venous thromboembolism is thought to contribute to 10% of deaths. In the community, incidence varies, depending on age, between 0.1 and 1/1000 per year.

Objective diagnoses of DVT (deep vein thrombosis) and PE (pulmonmary embolism) are important for three reasons � managing the current event, identifying and managing recurrent disease, and managing prophylaxis in high-risk situations such as pregnancy or surgery. The initial objective tests are ultrasound for DVT and lung scanning or helical CT for PE. A normal D-dimer level is a useful negative predictor for VTE.

Primary heparin therapy is essential for VTE and until recently this was administered by continuous intravenous infusion in hospital followed by outpatient warfarin. Low molecular weight heparins (qv) are now available which enable many patients with both DVT and PE to be treated on an outpatient basis. The low molecular weight heparin (LMWH) with dose adjusted for body-weight, is given subcutaneously once or twice each day for a minimum period of five days followed by warfarin. Using this approach more than 75% of patients will not require admission to hospital.

The duration of warfarin therapy depends on a variety of factors including extent and site of DVT (above or below the knee), and whether there is a temporary precipitating risk factor such as surgery, immobilisation or pregnancy:

calf vein thrombosis: � 6 weeks if associated with transient risk factor � 3 months for idiopathic disease


proximal DVT � 3 months if associated with transient risk factor � 6 months for more extensive or idiopathic disease

see also Hypercoagulability

Vibrio alginolyticus

An organism found in sea-water where it can cause significant infections of the external ear or wounds. It has been found, for example, on rope-burns in yachties or chronic ulcers in elderly people who bathe in sea-water. It is usually susceptible to amoxycillin-clavulanate and doxycycline.

Vibrio cholerae The causative organism of cholera. Occasionally found in Asian immigrants and on rare occasions in visitors to endemic areas. Fluid replacement is paramount. Treatment shortens the illness, reduces the volume of stools and fluid requirements, and decreases organism secretion. Treatment options are ciprofloxacin, 1g as a single dose; norfloxacin, 400mg 12-hourly for 3 days; or doxycycline, 300mg as a single dose.

Vibrio parahaemolyticus

Found in New Zealand and Japan in shell fish which, when eaten raw, can cause food poisoning. Treatment is fluid replacement. Most infections are self-limiting. Severe disease may benefit from treatment, using a cholera regime, but the benefit is likely to be small.


Virilism see Hirsutism/virilism

Virology

Despite the vast spectrum of disease caused by viruses, they are less often investigated by the laboratory than bacteria. They are harder to grow, harder to treat and the trivial viral infections tend to be self-limiting.

Specific tests are described under the alphabetic entry for each disease.

As with bacteria, identification is by growth of the organism, by detection of viral antigen, or by detection of antibodies.

Virus or its antigen Specimens can be faeces, throat swab, serum, vesicle fluid or CSF.

Antibodies IgM antibodies usually indicate current infection. IgG antibodies indicate past or present infection.

Diagnosis is established by an increase in titre of 4-fold or more on paired sera, the first collected as early as possible in the disease, the second after 2-3 weeks of illness.

Enquiries about specific tests can be directed to a clinical microbiologist.

Non-specific features of some viral compared with bacterial illnesses


Viral Bacterial

neutrophil count decreased increasedlymphocyte count increased unchanged

or unchangedblood film atypical (variant) shift to left in

lymphocytes neutrophil series

Viscosity Blood viscosity is increased in polycythaemia vera, macroglobulinaemia and in the late stages of myeloma. The test is not much used now.

Vitamin B12

specimen: serum

ref range: 160-600 pmol/L 140-160 pmol/L, borderline low

Normal absorption of B12 requires a non-vegetarian dietary source, a normal stomach to produce intrinsic factor, and a normal terminal ileum to absorb the B12/IF complex. A healthy person with replete body stores has enough B12 to last 3-6 years if no more is ingested.

Low B12 levels

Causes include:

• vegetarian diet


• drugs � oral contraceptives � metformin � other : methotrexate, colchicine, slow K, anticonvulsants, cimetidine, triamterene

• pregnancy � B12 levels are often low without tissue deficiency

• low B12 binding protein, transcobalamin I, which can be measured, but the expense is seldom warranted

• pernicious anaemia (qv)

• malabsorption

• inflammatory bowel disease: Crohn's disease, or ulcerative colitis in the terminal ileum

• previous gastrectomy or ileectomy

• primary folate deficiency

• Diphyllobothrium fish tapeworm infestation

Further investigation and treatment of low B12

If haematological abnormalities are present � raised MCV, anaemia, neutropenia, thrombocytopenia, oval macrocytes and hypersegmented neutrophils in the blood film � the underlying cause must be identified

If there are no haematological abnormalities and the patient seems healthy, there is less urgency. The level may be normal for that person or it may indicate early deficiency. It is a matter of clinical judgement and patient choice whether to investigate further at once; or follow-up in 6 months or so; or, for the person who believes in vitamin supplements, start a course of oral vitamin B12 or multivitamin supplements. There is also the group of patients who have unshakeable faith in B12 by injection.

The elderly often have low B12 and folate levels and may benefit from supplements.


Elevated B12 levels

• oral or parenteral vitamin B12 supplement • haematological disorders: myeloproliferative disorders, leukaemias, high

white cell counts • liver disease

Vitamin C see Ascorbic acid (Vitamin C)

Vitamin D

specimen: serum ref. range: 25-hydroxy-cholecalciferol 14-76 µg/L

1a, 25-dihydroxy-cholecalciferol 18-62 ng/L

When "vitamin D" is requested, the 25-hydroxy-cholecalciferol is measured.

Vitamin D levels decline with advancing age and many very elderly people, particularly women living in rest-homes, have levels low enough to contribute significantly to decrease in bone density.

There is debate whether vitamin D levels should be measured routinely in this group. Most will have low levels and it is probably more cost-effective to provide the cheaper forms of vitamin D supplement with calcium.


In general usage, "vitamin D" is loosely applied to the physiologically active hormone, calcitriol, and its precursors.

(sunlight on skin)

(in vivo) 7-dehydro-cholesterol

cholecalciferol (vitamin D3)

25-hydroxy-cholecalciferol

1α, 25-dihydroxy-cholecalciferol (calcitriol)

(in liver)

(in kidney)

(physiologically active)

(dietary) ergocalciferol (vitamin D2)

see also Osteoporosis/Osteomalacia

Vitamin K

Vitamin K is a fat-soluble vitamin which is essential for hepatic formation of functionally active prothrombin (Factor II) and coagulation Factors VII, IX and X. Although vitamin K is found in the diet, particularly green vegetables, the more important source is the normal bacterial flora of the bowel which synthesises the vitamin. Body stores last only 1-2 weeks if absorption stops.

Deficiencies of vitamin K and Factors II, VII, IX and X can be due to pre-hepatic or hepatic causes.


pre-hepatic intestinal malabsorption – coeliac disease, pancreatic disease, biliary obstructionbroad spectrum antibiotics altering the normal florawarfarin therapyneonates

hepatic advanced cirrhosissevere hepatitis

The Echis ratio (qv) helps distinguish between pre-hepatic and hepatic causes.

The prothrombin ratio (PR) and its standardised presentation, INR, are used to monitor vitamin K-dependent factor deficiencies and the anticoagulant effect of warfarin.

Vitamin K injections correct factor deficiencies due to lack of absorption or availability and are also used to correct a prolonged INR due to excess warfarin action.

see INR (international normalised ratio)

VLDL (very low density lipoproteins) In the fasting state, VLDL particles contain most of the plasma triglyceride and 10-15% of total cholesterol.

see also Lipoproteins Triglyceride Cholesterol


VMA (vanillyl mandelic acid) see HMMA (hydroxy methyl mandelic acid)

VTE see Venous thromboembolism (VTE)

von Willebrand's disease (vWD)

vWD, discovered in 1926 and the commonest inherited bleeding disorder, is due to a defect in the plasma von Willebrand factor (vWF) causing a secondary abnormality of platelet adhesion.

vWF, like fibrinogen and fibronectin, is an adhesive protein important in platelet attachment to subendothelial surfaces and in platelet-platelet interactions at sites of vessel injury. vWF also plays an important role in the stabilisation and protection of coagulant FVIII:C in plasma.

The most commonly encountered type of vWD is transmitted as an autosomal dominant trait. These patients usually have mild bleeding symptoms and mild to moderate abnormalities in the relevant laboratory tests (type I heterozygous vWD).

Testing for vWD

FVIII:C The coagulant activity of the FVIII : C protein.

von Willebrand Factor (vWF) Measured as the von Willebrand factor antigen (vWF:Ag). This large glycoprotein normally stabilises factor VIIIC and is variably reduced in vWD. vWF is essential for normal adhesion of platelets and therefore for a normal bleeding time.


von Willebrand factor activity (vWF:Activity) This is a functional activity which measures the vWF's ability to bind to the Glycoprotein 1b platelet binding site responsible for normal adhesion.

Collagen binding assay (CBA) The functional assay which measures the vWF's ability to bind to collagen. A discrepancy between the vWF antigen and the CBA suggests a variant form of vWD.

Ristocetin-induced platelet aggregation The functional activity of vWF measured as the ability of plasma vWF to agglutinate platelets in the presence of ristocetin. The assay is relatively sensitive and specific for vWD.

In the initial laboratory evaluation of patients suspected of having vWD, the following should be performed:

• Bleeding time • Platelet count • APTT • FVIII : C • FVIII : C • vWF Activity • CBA • Blood group • Ristocetin platelet aggregation (not routinely performed in all patients)

One or more of these tests are usually abnormal in patients who have vWD but the results may vary in the same patient with repeat testing. It is essential that the patient not be taking drugs which could affect the bleeding time. Most frequent offending agents are aspirin or other NSAIDs. Many conditions such as pregnancy, hypo- or hyperthyroidism, uraemia, recent exercise, infection or diabetes can affect the FVIII:C activity and vWF antigen levels. Individuals with blood group O have significantly reduced levels of the vWF:Ag and vWF activity compared with blood groups A, B or AB.


Patterns of Factor VIII results in vWD:

FVIII:c vWF:Ag vWF:Activity CBA Ag/CBA ratio

Normal Ν Ν Ν Ν Ν

Type 1 vWD Ν−↓ ↓ ↓ ↓ Ν

Type 3 vWD Absent Absent Absent Absent —

Type 2A vWD Ν−↓ Ν−↓ Ν−↓ ↓↓↓ ↑↑↑

Type 2B vWD Ν−↓ Ν−↓ Ν−↓ ↓ ↑

Type 2M vWD Ν−↓ Ν−↓ ↓↓ Ν−↓ Ν

Type N vWD ↓↓↓ Ν Ν Ν Ν

Notes: Type 1 is the usual heterozygous form of vWD Type 3 is very rare and presents like severe haemophilia Type 2 forms are the known variant forms of vWD. These are uncommon.

W

Warfarin anticoagulant therapy see INR (international normalised ratio)


Wasp venom see Bee and wasp venom allergy

WBC (white blood cell count) see Blood count

Weight loss

Consider:

• thyrotoxicosis • diabetes • eating disorder • malignancy • HIV

White blood cell antibodies

see Lymphocyte antibodies

White blood cell count and differential see Blood count


Whooping cough (pertussis) see Bordetella pertussis

Widal test see Salmonella antibodies (Widal Test)

Wound swabs see Skin and wound swabs.

Where clinical details indicate a deep-seated infection, anaerobic cultures will be set up.

WR (Wasserman Reaction) replaced by VDRL/RPR

see Treponemal serology (STS, serological tests for syphilis)

Wuchereria bancrofti see Filariasis


X

X-match see Crossmatch

d-Xylose test

A test formerly used for malabsorption but now discontinued because of lack of specificity and sensitivity.

Y


Yaws

All STS (serological tests for syphilis: RPR/VDRL, TPHA FTA) are positive in those who have had yaws which is endemic in the Pacific, and positive STS in a Pacific Islander are often due to yaws.

see Treponemal serology (STS, serological tests for syphilis)

Yeasts

Yeasts grow readily from ordinary bacterial swabs and cultures. Candida albicans (qv), the principle human pathogen, is a member of the normal flora of the gut. Other species of Candida are also common and may cause clinical infection.

Yersinia enterocolitica A pathogen which is being isolated with increasing frequency from cases of infectious diarrhoea - currently about 10% of the total.

Yersinia spp. are frequently present in the intestinal tract of wild and domesticated clinically healthy birds and animals. In New Zealand, Y. enterocolitica has been recovered from pigs, cattle and dogs. Processed meat ready for sale has only rarely be shown to be contaminated with Yersinia. The source of most cases of Yersinia infection is unknown.

Some patients develop an abdominal pain syndrome which may last for weeks. The most likely cause for this is intra-abdominal lymphadenopathy.


Y. enterocolitica is susceptible to cotrimoxazole, tetracycline and fluoroquinolone but antibiotics do not shorten the diarrhoea which usually settles spontaneously in 3-10 days.

Infections tend to be sporadic rather than epidemic and are found world-wide. It can cause terminal ileitis which mimics acute appendicitis presenting as right lower quadrant pain, fever and leucocytosis. Some patients develop a reactive arthritis.

Yersinia has been transmitted by blood donated by asymptomatic donors. Patients who have Yersinia-associated diarrhoea should inform the blood collection service if they donate blood over the next six months.

Z

Zarontin (ethosuxiamide) see Anticonvulsants

Zinc, plasma specimen: blood, trace metal tube, patient must be fasting ref. range: 12 - 20 - µmol/L

Plasma levels are an indifferent measure of body stores.


Zinc deficiency in New Zealand can occur in patients on renal dialysis or parenteral nutrition and in conditions involving chronic loss of protein and electrolytes. Some drugs, including steroids, diuretics and anticonvulsants, may reduce zinc levels. The rare recessive condition acrodermatitis enteropathica is associated with an isolated malabsorption of zinc. Reported possible symptoms of deficiency include loss of appetite, poor taste, dermatitis, abdominal pain, diarrhoea, decreased growth and sexual development, and infertility.

Health food shops sell zinc supplements to boost the immune system and cure colds and topical preparations may promote healing of wounds and ulcers. Plasma levels do not give useful information in these situations - better to try the products and see if they work.

More serious levels of zinc deficiency are found in developing countries where the high phytate content of cereal diets binds zinc. In 1961a group of anaemic clay-eating Iranian dwarfs with rough dry skin and absent secondary sex characteristics were shown to be zinc deficient and their troubles corrected by oral zinc sulphate.

Zinc toxicity has been described in welders inhaling zinc oxide fumes causing metal-fume fever or brass chills.

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