variable control in quality assurance (2)

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Variable Control In

Quality Assurance



Sources, Types &

Documentation of Errors inClinical Laboratories



Laboratory Analysis

The goal of laboratory analysis

is to provide the reliablelaboratory data to the health-

care provider in order to assist

in clinical decision-making.



Modern medicine relies on the provision of

accurate analytical results from the laboratory

both to confirm diagnosis and to monitor therapy.

If laboratory results are to play a proper role indiagnoses and treatment then they must be

trustworthy

Experience has shown that all analytical results are

subject to errors arising from a variety of causes It is essential that these errors be kept to a

minimum.

Laboratory Analysis



QA in Laboratories

The assurance of high-uality laboratory results relies

on a commitment to all aspects of the testing system!

including attention to"

1. Preanalytical factors are those factors that affect the

laboratory results due to handling of the specimensample prior to analysis.

2. The analytical phase includes verification of instrument

linearity! precision! accuracy! and overall reliability

through the use of standard materials! quality control(QC) samples! procedures! and #$ rules.

3. Postanalytical factors include timely and accurate

laboratory result reporting and other aspects that occur

after the analysis phase.



Quality assurance has been defined by %&' as"

The total process whereby the uality of the laboratoryreports can be guaranteed. It has been summari(ed asthe"

Right result! at the

Right time! on the

Right specimen! from the

Right patient! ith the result interpretation !ase" on#

Correct reference data! and at the

Right price.

WH Definition



Quality Assessment

$efinition#uality assessment or uality

assurance )#*+ is a complete systemof creating and following procedures

and policies to aim for providing the

most reliable patient laboratory results

and to minimi(e errors in thepreanalytical! analytical! and

postanalytical phases.



%rror, Error is the discrepancy

between the result obtained inthe testing process and its True

alue/ 0 *ccepted True alue/



&ources of %rror, 1eagents

, 2tandards

, Techniue

, Environment

, 2pecimen collection! handling etc., Many more



The importance clinical la!oratory

results,3se of clinical laboratory test results in

diagnostic decision making has become

an integral part of clinical medicine.,More than 45-657 of the most

important decisions on admission!

discharge! and medication are based onlaboratory test results.



The impact of la!oratory errors$onseuences of lab errors! therefore! have

implications on8.9atient: unnecessary treatment.

;.<octor: failure to provide the proper

treatment.

=.$ommunity: poor healthcare service.

>.?aboratory: bad reputation.

These conseuences result in increased cost

in time! personnel effort! and often in poorpatient outcomes.Therefore minimi(ing lab

errors is a major task in lab management.



%rrors in clinical la!oratory, *n @error@ is a deviation from accuracy or correctness.

,?aboratory errors may be defined as Aany defect fromordering tests to reporting and appropriately interpreting

resultsB., Errors in laboratory medicine occur most often in all

testing process phases )pre-analytical! analytical andpost-analytical steps+.

,It is the responsibility of the lab manager to minimi(e

lab errors occurring at any phase of the testing process.

,Monitoring and control of lab errors is therefore animportant challenge in the management of clinical labs

so as to produce reliable test results as soon as

possible and thereby achieve better lab performance.



Sources of Error

Erroneous results are at best a nuisance: at worst! they

have potential for causing considerable harm.

Errors can be minimi(ed by careful adherence to robust!

agreed protocols at every stage of the testing process"this means a lot more than ensuring that the analysis is

performed correctly.

Errors can occur at various stages in the process"

pre-analytical! occurring outside the laboratory! analytical! occurring within the laboratory!

post-analytical! whereby a correct result is generated

but is incorrectly recorded in the patient@s record!



PR'C%&& P'T%T*+ %RR'R&

Test ordering

, Inappropriate test, &andwriting not legible

, %rong patients I<, 2pecial reuirements not specified

2pecimenacuisition

, Incorrect tube or container

, Incorrect patient I<, Inadeuate volume, Invalid specimen )hemolysed or diluted+, $ollected at wrong time, Improper transport conditions

,1- Preanalytical errors



!a" Specimen collection an# $an#lin%

* test result is no better than the uality of the specimenreceived in the laboratory.

2pecimen collection and handling procedures must beexplained to all parties involved in the processing of

specimens ) nursing personnel! physician assistants! andhealth-care professionals+ ?aboratory personnel are responsible for

for training other personnel involved in specimen collectionand transport and for communicating effectively in order tomaintain optimal uality of specimens for laboratory

testing. minimi(ing preanalytical errors based on acceptance or

rejection of the received specimens. 2ince preanalytical errors seem to make up the majority of

most laboratory test problems! proper training is an important

area to address.



!b" Hemolysis

&emolysis is generally a preanalytical problem thatcan be avoided.

It is graded based on visible presence of hemoglobin!when greater than ;5 mg0d?! and it is often graded as

mild! moderate! or gross hemolysis. Cross hemolysis will often impact on almost every

test method due to release of intracellular constituents into the serum

)potassium! phosphates! ?<&! and *2T+ and colorimetric interference due to pigments.

Crossly hemoly(ed specimens should always berejected.



!c" Specimen Contamination

The type of blood specimen contamination resulting from I fluids

would vary with the type of fluid being infused.

* dextrose solution )sugar+ I infusion would yield

extremely high glucose results in venous specimens

collected above or near the infusion area. Total parenteral nutrition )T9D+ fluid contains most of the

reuired daily nutrients for a person who can/t ingest food.

T9D fluid contamination in a specimen creates gross

tur!i"ity along with elevated lipid and glucose values and

potassium levels too high to be compatible with life. In specimens from a patient receiving a saline I infusion!

2odium and chloride results will be falsely elevated due to

contamination from saline I fluid.



!#" Specimen Transport

Many chemical compounds are stable within plasma

or serum in itro for only a short time.

?evels of potassium! ammonia! lactate! bilirubin!

glucose! $'; ! sodium! urea! and alkaline

phosphatase! for example! are particularly affected

by contact with blood cells! which can continue to

undergo cellular metabolic processes after blood has

been removed from the body.

E.g. Clucose will decrease as much as 8;7 perhour if not separated from blood cells or

preserved.



!e" Specimen Transport



!f" A##ities to 'loo#

3sing the wrong additives or the wrong amount ofadditive can cause adverse effects on blood specimens. 2odium oxalate! sodium fluoride! or sodium heparin cannot

be used for samples needed for sodium analysis

because they increase the level of sodium. *mmonium heparin should not be used for specimens

intended for plasma ammonia or urea testing because it adds to the chemical being measured.

2odium fluoride cannot be used for en(yme analysis samples because fluoride acts as an inhibitor to most en(yme activity.

Ethylenediaminetetra-acetic acid )E<T*+! sodium citrate! andsodium oxalate cannot be used in samples that will be usedfor mineral analysis because they remove calcium and magnesium.



!%" Sample (reparation

2ample preparation involves processing of the

sample prior to and in preparation for analysis.

9rocessing involves centrifugation!

and making an aliuot of the specimen ina test tube or sample cup

eep in mind that clotted or whole blood cells

can affect chemicals in the sample over a

period of time! such that additional chemicals

arise or some chemicals are consumed



It is very difficult to establish effective methods for

monitoring and controlling preanalytical variables

because many of the variables are outside the laboratory

areas.

1euires the coordinated effort of many individuals and

hospital departments

9atient Identification

The highest freuency of errors occurs with the useof handwritten labels and reuest forms. The use of

bar code technology has significantly reduced I<

problems.

/ow To Control Preanalytical %rrors



2o!F"

8.Training of personnel for proper collection and

handling of samples! including adherence to

specific steps and maintaining turnaround timeinvolving sample receiving and processing.

;.3se of well-written procedures and policies can

help to minimi(e preanalytical errors )specimen

collection manual+



*nalytical 0easurement

, nstrument not cali!rate"

Correctly

, &pecimens mi up

, ncorrect olume of specimen

, nterfering su!stances present

, nstrument precision pro!lem

,2- *nalytical errors



Test interpretation

, Preious alues not aaila!lefor comparison

Test reporting

, rong patient $

, Report not legi!le

, Report "elaye"

, Transcription error

,3- Post *nalytical errors



Analytical ariables an# Quality Control

The ideal analytical method is accurate! precise!sensitive and specific. *ccurate" It gives a correct result

9recise" that is the same if repeated 2ensitive" It measures low concentrations of the

analyte 2pecific" is not subject to interference by other

substances

In addition! it should preferably be cheap! simple anduick to perform.



There are many analytical variables that must becarefully controlled"

%ater uality $alibration of analytical balances $alibration of volumetric glassware and pipettes 2tability of electrical power 2tability of temperature of heating baths!

refrigerators! free(ers and centrifuges

Control of analytical aria!les



$ocumentation



, <ocumentation is a process of providingwritten information about the laboratory

testing process. There are many methods

to make documentation for yourlaboratory such as

8.&ard documentation )written information

in paper sheets+.;. 2oft documentation )computer

program+.



, <ocumentation should include"-

8. Test procedures.

;. %ork instructions.=. 1eceiving sample and registration.

=. Test results and uality control results.



These are also referred to as laboratory benchmanual

Important features of 2'9/s *pplica!le and aaila!le in the laboratory

where they will be used Clearly written and easy to understand and

follow ept up to "ate using appropriate

technologies

Stan#ar# peratin% (roce#ures

!S(s"



The 2tandard operating 9rocedure should contain the

following"

9rocedure name $linical significance 9rinciple of method 2pecimen of choice 1eagents and euipments

9rocedure 1eference values $omments 1eferences



)et$o# Vali#ation

Method validation should be performed

before a test procedure is placed into routine

use.

alidation may be accomplished bythoroughly testing reference materials or by

comparison of results of tests performed by

an alternative method.



Method validation should provide evidence of

the following"

*ccuracy 9recision

2ensitivity

2pecificity

?inearity



I#eal Test

*n ideal diagnostic test would be"

8557 sensitive! giving positive results in all diseased subjects!

and also 8557 specific! giving negative results in all subjects free of disease.

Individual tests do not achieve such high standards.

Gactors that increase the specificity of a test tend to

decrease the sensitivity and vice versa.



If it were decided to diagnose thyrotoxicosis only if theplasma free thyroxine concentration were at least =;pmol0? )the upper limit of the reference range is ;4

pmol0?+! the test would have 8557 specificity: positive results

)greater than =; pmol0?+ would only be seen inthyrotoxicosis.

'n the other hand! the test would have a lowsensitivity in that many patients with mildthyrotoxicosis would be misdiagnosed.

If a concentration of ;5 pmol0? were used! the test would be very sensitive )all those with

thyrotoxicosis would be correctly assigned+ but havelow specificity!

because many normal people would also bediagnosed as having thyrotoxicosis.



Linearity

The linear

range is the concentration range

over which the measured concentration is

eual to the actual concentration without

modification of the method. The wider the linear rang! the less freuent

will be specimen dilution



Linearity

* uantitative analytical method is said to belinear when" the measured value from a series of sample

solutions is linearly proportional to the actualconcentration or content of the analyte )truevalue+ in the sample solutions.

The points at the upper and lower limits of theanalytic measurement range that acceptablyfit a straight line determine the linear range.

variable control in quality assurance (2)

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