AccuracyAgreement between your test result value and the true value; i.e. how correct your result is.AffinityAn attractive force between substances or particles that causes them to enter into and remain in chemical combination, for example; the binding of antibody to antigen.AggregationThe grouping of units or parts into a mass or whole.AliquotThe division of a sample into at least two smaller size vials.AmplificationAmplification generally means an addition to or expansion of a statement or idea. In medical terminology, amplification refers to the selective copying of a gene or any sequence of DNA. This occurs naturally in the body in order to satisfy the increased requirement of individual cells for gene products such as proteins. Amplification also plays a role in cancer cells when a tumour cell copies DNA segments as a result of cell signals or external environmental factors. Artificial amplification is conducted due to its central role in gene research.AnalyteThe chemical substance being measured in an assay, usually contained in blood or other body fluids. AntibodyA protein produced by our body in response to an antigen. There are 5 classes of antibodies (IgG, IgM, IgE, IgA, IgD). The antibody binds to and neutralises the antigen.AnticoagulantA substance that stops the blood from clotting.Antigen

Antigens are usually foreign substances which enter the body and trigger the immune system to produce antibodies in order to fight off the potential infection. Antigens can be toxins, foreign blood cells, bacteria or the cells of transplanted organs.

AntimicrobialThe term given to a group of drugs that inhibits the growth or destroys microorganisms.Antioxidant

A molecule that protects cells from oxidative damage of oxygen and free radical molecules that are chemically unstable and cause random reactions damaging proteins nucleic acids and cell membranes.

Antiserum

A solution of antibody or mixture of antibodies either purified or un-purified used in the manufacture of diagnostic reagents or used as a component of a diagnostic kit.

Assay

A diagnostic test to measure the concentration or level of a particular analyte.

Assay Range

The assay range describes the highest and lowest concentrations, at which a reaction is still measurable.

Aspiration

The withdrawal of fluid or tissue, e.g. by a wash probe on an analyser.

Aqueous

The term aqueous simply means dissolved in water.

bacteremia - the presence of bacteria in the blood.

benign - not malignant; not recurrent; favourable for recovery.

biopsy - removal and examination, usually microscopic, of tissue from the living body, performed to establish a precise diagnosis

bradycardia - abnormally slow heart action.

Benchtop

This term simply refers to a position of an object, i.e. ‘on top of a bench’. However, in a scientific setting, it is used to describe an analyser which is small enough to fit on top of a laboratory workbench but is too large to be a point of care system.

Biochemistry

Biochemistry is the study of the chemical structures and vital processes which occur in living organisms. Biochemists study the compounds in the body and how these result in chemical processes. They seek to understand such processes both within healthy and unhealthy organisms.

Blood Clotting

Blood clotting, also known as coagulation performs the vital task of preventing excessive blood loss in the event of injury. Leakage of blood is prevented by the blood cells sticking to the wound. However, clotting can sometimes fail to occur, this is known as haemophilia.

Blood Gas Analysis

The body has many functions, one critical function is to transport substances such as oxygen, carbon dioxide, nutrients and excretions. Most of these substances are gases; therefore blood gas analysis determines their concentrations in arterial and venous blood.

Blood Screening

Blood screening is used to detect pathogens which cause symptomless diseases. An effective diagnosis then allows correct treatment to begin in good time, thus improving the patient outcome. Blood screening is also performed on donated blood to identify and remove any infected blood.

Calibration

The process of setting up or standardising an assay using a calibrator or standard of known concentration.  When the data generated is analysed this can then be used to calculate results for any subsequent sample of unknown concentration.  It adjusts the accuracy of an assay method.

Calibrator

A material, generally serum based with an accurately assigned analytical value, used to calibrate diagnostic assays.

Centrifugation

Centrifugation is a process used to separate or concentrate materials suspended in a liquid medium by use of the centrifugal force.

Clinical Chemistry

This field deals with analysing blood, urine and other body fluids. Their constituents i.e. proteins and enzymes are determined. The results from this analysis is used as a basis for patient diagnosis.

Control

A serum based material with assigned target values and acceptable ranges to evaluate the accuracy and reproducibility of a diagnostic assay.

CSF

Cerebrospinal fluid. 

Cuvette

A reaction vessel (similar to a tube) used in photometric analysers.

Cytopathology

Also histopathology; the study of tissue samples of patients to detect diseases.

Diagnostic Kit

A combination of reagents liquid or freeze-dried which can be used in a laboratory to measure specific serum or urine parameters to diagnose and monitor the therapy of specific diseases.

Disease Marker

A disease marker is any serum component which rises or falls outside its normal range in response to disease.

Freeze Drying

Also called lyophilisation, is a process in which an unstable mixture of chemicals can be stabilised by removing water and then sealed under a vacuum in a glass vial.

Haematology

The study of blood and its components. Blood is an important transport mechanism for essential nutrients. Haematology studies disorders associated with blood such as coagulation.

Haemoglobin

The protein in the centre of a red blood cell (erythrocyte), that is responsible for binding and delivering oxygen to the body. It also gives blood its red colour.

Haemolysis

Lysis of red blood cells with liberation of haemoglobin; a haemolysed sample is red.

Half-life

The time required to break down and eliminate half the concentration of a substance. At half the concentration a drug stops being effective, so the half-life indicates the amount of time that a drug will be effective.

In Vitro

A procedure carried out outside a living organism.

In Vivo

A procedure carried out within a living organism.

Limit of Detection (LOD)

The LOD refers to the smallest quantity of analyte that can be detected and distinguished from the blank with a reasonable degree of certainty.

Lyophilised

The term lyophilised refers to a material that has been freeze-dried.  Freeze-drying is a process by which an unstable mixture of chemicals can be stabilised by removing water and then sealed under a vacuum in a glass vial.

Lysis

A process of disintegration or dissolution of cells. For example, haemolysis is the dissolution of red blood cells.

Manual

In manual tests the functional steps are carried out by hand and the reactions measured using a spectrophotometer.  Results are not produced directly and the operator will generally have to perform calculations or plot a graph to generate meaningful data.

Microbiology

The study of microorganisms, such as bacteria, viruses and parasites.

Microarray

Microarrays consist of many probes attached chemically to a substrate with a very small surface. This surface could be a glass slide or a microchip. Each probe, which holds genetic information, can detect many different genes at the same time. Microarrays can be used to assist in the detection of genetic variations.

Near patient testing

This term is used to describe a rapid diagnostic test or testing platform which allows clinicians to respond quickly to critical situations. Near patient testing can be performed in a doctor’s office, in the emergency room or other near patient sites. It enables the clinician to decide on diagnosis and potential treatment at the site of testing, for a rapid diagnosis thus improving patient outcome.

Normal Range

The normal range refers to the results expected from a healthy individual.  It is important to note that results may vary with age, gender and geographical location.

Oncology

This field of medicine examines tumours and cancerous conditions and the subsequent treatment options as well as diagnosis.

Pathogen

A specific causative agent of disease such as bacterium, virus or chemical etc.

Plasma

The clear amber liquid which is derived from whole blood that has been collected in the presence of an anticoagulant in such a way as to prevent clot formation.  Plasma differs from serum in that it contains all the clotting factors and fibrinogen which are lost on clot formation.

Point of Care (POC)

The term used for diagnostic testing which takes place at or near the patient’s site of care.

Precision

Precision refers to the reproducibility of test results and is a measure of how disperse the values are.  Inter-assay and Intra-assay are two distinct measures of this.

Proliferate

To grow by rapid production of new cells.

Quality Control

The process of detecting errors in any manufacturing or operational system. In the case of diagnostic testing it refers to the accuracy and reliability of the diagnostic result generated.

Reagent

A component of a kit used to carry out a chemical reaction to determine levels of different analytes.

Reconstitution

The addition of water to a freeze-dried reagent or control material to return it to its former condition.

Sensitivity

The ability to detect small quantities of a measured component.

Serum

The clear amber liquid that is derived from clotted blood by centrifuging and removing the red blood cells.  Serum is a complex mixture of hundreds of different proteins, sugars, fats and salts and is the starting material for most diagnostic tests.  Many control products are serum based to ensure the matrix is the same as the patient sample.

Specificity

The ability of a method to measure solely the component of interest.

Standard

An aqueous solution containing a known level or concentration of analyte that will not change and can be used to calculate diagnostic results.  Normally used to calibrate manual or semi-automated tests.

Substrate

The specific biochemical compound or compounds which an enzyme will act upon and convert into product.

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Blood Bank (Immunohematology)--We all know of the responsibility of the blood bank in obtaining, storing, and dispensing blood for transfusions. There are other functions including: obtaining and handling other blood products, some of which are rare; and also research in blood transmitted diseases.Clinical Chemistry--This section of the lab performs analyses on whole blood, serum, plasma, urine, and other biological specimens like cerebrospinal fluid, am-niocentesis fluid, pleural fluid, periton-eal fluid, and feces.Clinical Microbiology--This section of the lab is involved with a variety of biological specimens such as: urine, feces, blood, sput-um, CSF, drainage, exudates, nail, skin, tissue, and swabs from throat, wounds, and other such specimens.Clinical Pathology--Clinical pathology refers to the section of the pathology lab which applies to the problem of find-ing solutions to the problems found in the clinical areas. The members of this team in-clude medical tech-nologists, medical scientists, tech-nicians andpathologists. Together they perform tests and inves-tigations into all aspects of disease, including preven-tion, diagnosis, and treatment. Cytology--Cytology is the study of the individual cells. This department has cytologists and cyto-technologists who are trained toperform prelimi-nary screening on cells. Any of these suspicious cells are then usually examined by the pathologi-st.Cytogenics--Cytogenics is the branch of genetics that studies cellular components concerned with heredity; primarily the structure, function, and origin of the chromosomes.Diagnostic Test--A Diagnostic Test is an inquiry into a pathological condition. A diagnostic test can be thought of as any test used to help diagnose a pathological condition.Erythrocyte--An erythrocyte is a mature Red Blood Cell. Immature red blood cells cannot carry oxygen. Immature red blood cells are true cells and contain a nucleus. The erythrocyte has lost its nucleus and then it "technical-ly" cannot be called a cell. It is a corpuscle.However, many persons still refer to erythrocytes as Red Blood Cells or RBC's.Fasting Specimen--Instruct the patient not to eat or drink after midnight the night before the test. Do not eat or drink in the morning before the specimen is collected. It is usually a good idea to place a sign on the bed to be sure no one gives the patient food. Again, check with hospital policy, and lab policy. The patient may be allowed small amounts of water prior to some tests.First Voided Specimen (First morning specimen)--As the name implies, the first specimen of the day is to be obtained. However, some facilities insist the specimen be at a certain time in the morning. Be sure to check policy at your facility.Hematology--This department is responsible for the quantification of cellular elements, including red and white blood cells and platelets. Many of the tests are today performed by electronic means. However, some of the tests are performed by manual means. Many nurses may have closer contact to this depart-ment than most other departments of the lab. Thereason for -this is that the hematology section performs those tests often seen in patients who are on chemothera-py, an-ticoagulant therapy, and cardiac therapy, and have frequent blood cell evalua-tions. Blood coagulation studies are also performed in this section of the lab. Thediagnosis and treatment of blood clotting disorders are the two most important functions of this section.Hemoglobin--Hemoglobin is the main component of Red Blood Corpuscles (RBC's). Hemoglobin is a conjugated protein that "carries" oxygen and transports it to all the body cells. Hemoglobin also carries carbon dioxide from the tissues to the lungs for excretion. Three major types of hemoglobin are found in normal blood; they are: Hgb A, Hgb A2, and

Hgb F.Histology--Histology is the study of the microscopic structure of tissues and cells. Histology technicians prepare frozen sections and surgical and autopsy tissues by slic-ing them to less than paper thickness, mounting them on slides, and finally staining them with special dyes. The slides will then be examined and inter-preted, usually by a path-olo-gist.Plasma--Plasma is the liquid portion of whole blood after centrifuging. Whole blood is spun in a centrifuge removing the solid portions of the blood, such as red and white blood cells and other solid particles. The plasma is thick and rich with dissolved chemicals and other substances such as proteins and other chemicals.Random Sample--The term random, refers to taking a sample (any sample) at any time during the day (or night). Random means that you do not have to take the sample at a particular time. Sometimes the sample may have other stipulations. You might have to take the sample on a certain day. If the test is ordered today, you generally take the sample today(unless ordered differently).Second-Voided Urine Specimen--This is a urine sample obtained after the patient has emptied his/her bladder. Generally the second sample is obtained 30 minutes after the patient has emptied the bladder. However, some hospitals have different policies for this time interval. Some hospitals will have you wait until the patient is ready to void again.Always check with your hospital policy.

LIVER FUNCTION TESTS (L.F.T.)The following set of tests is commonly used to diagnose liver disease. Almost all types of Liver disease can be isolated by the use of these following tests. Liver disease is fairly common today, so these tests are of particular significance in the diagnosing of these related diseases.

Serum BilirubinThis test is a measure of the bilirubin in the blood.Normal Value:total bilirubin = less than 1.5 mg/100mlClinical Implications:Bilirubin is present in blood at all times due to the break down of hemoglobin which occurs all the time. Normally, bilirubin is removed from the blood by the liver. Increased serum bilirubin levels indicate obstructive disease of the liver, hemolysis or actual liver cell damage.

Alkaline PhosphataseThis is a liver enzyme test. Alkaline phosphatase (ALP) is produced in the liver and bone, it is also derived from the kidney, intestine, and placenta. In obstructive biliary disease, there is elevated serum ALP.Clinical Implications:This test is very useful for diagnosing biliary obstruction. Even in mild cases of obstructive disease, this enzyme is elevated. It is not very useful for diagnosing cirrhosis. If a patient has bone disease, this test may be highly inaccurate, as ALP is also found in bone tissue.

PROCEDURES FOR THE PURIFICATION OF PROTEINSProtein purification is an activity that has occupied the time of biochemists and molecular life scientists throughout the last two centuries. In fact, a large percentage of the biochemical literature is a description of how specific proteins have been separated from thousands of other proteins and other biomolecules in tissues, cells, and biological fluids. Biochemical investigations of all biological processes require, at some time, the isolation, purification, and characterization of a protein. In contrast to the repetitive procedures for isolation of DNA andRNA(see Chapter 9, Section B, p. 275), there is no single technique or sequence of techniques that can be followed to isolate and purify all proteins. It is sometimes still necessary to proceed by trial and error. Fortunately, the experiences and discoveries of thousands of scientists have been combined so that, today, a general, systematic approach is available for protein isolation and purification.

Amount of Protein Versus Purity of Protein Versus ExpenseThe procedure selected for protein purification is dependent primarily on how much of the protein is needed and how pure the protein must be; in other words, what is the purpose for isolating the protein? In terms of amount, one usually thinks on two scales: preparative, isolation of larger quantities (several milligrams or grams) to use for further characterization or structure and function studies; or analytical, isolation of microgram or milligram quantities in order to make a few precise measurements such as molecular weight, sequencing, or structure determination by NMR or X-ray diffraction. In terms of purity, a protein sample is considered pure when it contains a single type of protein. It is not practically possible to obtain a protein in 100% purity, but most studies can be done on samples that are 90–95% pure. It often is not worth the extra time and reagent expense to purify a protein greater than 90% unless absolutely necessary. In general, the best purification scheme is one that yields the maximum (or appropriate) amount of the protein, of desired purity, with a minimum amount of time and expense. The following discussion outlinesthe basic steps available to develop a protein purification scheme

Basic Steps in Protein PurificationDevelopment of Protein AssayFirst and foremost in any protein purification scheme is the development of an assay for the protein. This procedure, which may have a physical, chemical, or biological basis, is necessary in order to determine quantitatively and/or qualitatively the presence of the specific protein. During the early stages of the purification, the particular protein desired must be distinguished from thousands of other proteins present in the crude cell homogenate. The desired protein may be less than 0.1% of the total protein. It should be obvious that thegeneral protein assays (spectrophotometric, Bradford, Lowry, etc.; see Chapter 3, Section B, p. 67) are not useful as assays for a specific protein, because they simply indicate the total protein present. If the desired protein is an enzyme, the obvious assay should be based on biological function, that is, a measurement of the enzymatic activity after each isolation–purification step. If the protein to be isolated is not an enzyme or if the biological activity is unknown, physical or chemical methods must be used. One of the most useful analyticalmethods is electrophoresis. If an antibody has been prepared against the desired protein, it may be analyzed by electrophoresis and monitored during purification using Western blotting (see Chapter 6, Section C, p. 192).Preparation of the Crude ExtractOnce the protein source has been selected, the next step is to release the desired protein from its natural cellular environment and solubilize it in aqueous solution. This calls for disruption of the cell membrane without damage to the cell contents. Proteins are relatively fragile molecules, and only gentle procedures are allowed at this stage. The gentlest methods for cell breakage are osmotic lysis, gentle grinding in hand-operated glass homogenizers, and disruption by ultrasonic waves. These methods are useful for “soft tissue,” as found in greenplants and animals. When dealing with bacterial cells, in which rigid cell walls are present, the most effective methods are grinding in a mortar with an inert abrasive such as sand or alumina, or treatment with lysozyme and/or a detergent. Lysozyme is an enzyme that catalyzes the hydrolysis of polysaccharide moieties present in cell walls. When very resistant cell walls are encountered (yeast, for example), the French press must be used. Here the cells are disrupted by passage, under high pressure, through a small hole.Osmotic lysis consists of suspending cells in a solution of relatively high ionic strength. This causes water inside the cell to diffuse out through the membrane. The cells are then isolated by centrifugation and transferred to pure water.Water rapidly diffuses into the cell, bursting the membrane.Ultrasonic waves, produced by a sonicator, are transmitted into a suspension of cells by a metal probe . The vibration set up by the ultrasonic waves disrupts the cell membrane, releasing the cell components into the surrounding aqueous solution.Stabilization of Proteins in a Crude ExtractContinued stabilization of the protein must always be considered in protein purification processes. While the protein is inside the cell, it is in a highly regulated environment. Cell components in these surroundings are protected against sudden changes in pH, temperature, or ionic strength and against oxidation and enzymatic degradation. Once the cell wall/membrane barrier is destroyed, the protective processes are no longer

functional and degradation of the desired protein is likely to begin. An artificial environment that mimics the natural one must be maintained so that the protein retains its chemical integrity and biologicalfunction throughout the purification procedure. What factors are important in maintaining an environment in which proteins are stable? Although numerous factors must be considered, the following are the most critical:1. Ionic strength and polarity The standard cellular environment is, of course, aqueous; because of the presence of inorganic salts, though, its ionic strength is relatively high. Addition of KCl, NaCl, or MgCL2 to the cell extract may be necessary to maintain this condition. Proteins that are normally found in the hydrophobic regions of cells (i.e., membranes) are generally more stable in aqueous environments in which the polarity has been reduced by the addition of 1 to 10% glycerol or sucrose.2. pH The pH of a biological cell is controlled by the presence of natural buffers. Since protein structure is often irreversibly altered by extremes in pH, a buffer system must be maintained for protein stabilization. The importance of proper selection of a buffer system cannot be overemphasized. The criteria that must be considered in selecting a buffer arediscussed in Chapter 3, Section A, p. 57. For most cell homogenates at physiological pH values, Tris and phosphate buffers are widely used.3. Metal ions The presence of metal ions in mixtures of biomolecules can be both beneficial and harmful. Metal ions such as and may actually increase the stability of dissolved proteins. Many enzymes require specific metal ions for activity. In contrast, heavy metalions such as and are deleterious, particularly to proteins that depend on sulfhydryl groups for structural and functional integrity. The main sources of contaminating metals are buffer salts, water used to make buffer solutions, and metal containers and equipment. To avoid heavy-metal contamination, you should use high-purity buffers, glass-distilled water, and glassware specifically cleaned to remove extraneous metal ions (see Chapter 1, Section C, p. 15). If metal contamination still persists, a chelating agent such as ethylenediaminetetraacetic acidmay be added to the buffer.

4. Oxidation Many proteins are susceptible to oxidation. This is especially a problem with proteins having free sulfhydryl groups, which are easilyoxidized and converted to disulfide bonds. Areducing environment can be maintained by adding mercaptoethanol, cysteine, or dithiothreitol to the buffer system.5. Proteases Many biological cells contain degradative enzymes (proteases) that catalyze the hydrolysis of peptide linkages. In the intact cell, functional proteins are protected from these destructive enzymes because the enzymes are stored in cell organelles (lysosomes, etc.) and released only when needed. The proteases are freed upon cell disruption and immediatelybegin to catalyze the degradation of protein material. This detrimental action can be slowed by the addition of specific protease inhibitors such as phenylmethylsulfonyl fluoride or certain bioactive peptides. These inhibitors are to be used with extreme caution because they are potentially toxic.6. Temperature Many of the above conditions that affect the stability of proteins in solution are dependent on chemical reactions. In particular, metal ions, oxidative processes, and proteases bring about chemical changes in proteins. It is a well-accepted tenet in chemistry that lower temperatures slow down chemical processes. We generally assume that proteins are more stable at low temperatures. Although there are a few exceptions to this, it is fairly common practice to carry out all procedures of protein isolation under reduced-temperature conditions (usually in ice bath, ).

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Many clinical tests are used to confirm or refute the presence of a disease or further thediagnostic process. Ideally such tests correctly identify all patients with the disease, and similarly correctly identify all patients who are disease free. In other words, a perfect test isnever positive in a patient who is disease free and is never negative in a patient who is in factdiseased. Most clinical tests fall short of this ideal.Sensitivity, specificity, andother termsThe following terms are fundamental to understanding the utility of clinical tests:1. True positive: the patient has the disease and the test is positive.2. False positive: the patient does not have the disease but the test is positive.

3. True negative: the patient does not have the disease and the test is negative4. False negative: the patient has the disease but the test is negative.When evaluating a clinical test, the terms sensitivity and specificity are used. They are independent of the population of interest subjected to the test. The terms positive predictive value (PPV) and negative predictive value (NPV) are used when considering the value of a test to a clinician and are dependent on the prevalence of the disease in the population of interest.

SensitivityThe sensitivity of a clinical test refers to the ability of the test to correctly identify thosepatients with the disease.

Sensitivity =True positives True positives + False negativesA test with 100% sensitivity correctly identifies all patients with the disease. A test with

80% sensitivity detects 80% of patients with the disease (true positives) but 20% with the

disease go undetected (false negatives). A high sensitivity is clearly important where the test is used to identify a serious but treatable disease (e.g. cervical cancer). Screening the femalepopulation by cervical smear testing is a sensitive test. However, it is not very specific and ahigh proportion of women with a positive cervical smear who go on to have a colposcopyare ultimately found to have no underlying pathology.

SpecificityThe specificity of a clinical test refers to the ability of the test to correctly identify thosepatients without the disease.Specificity =True negatives True negatives + False positivesTherefore, a test with 100% specificity correctly identifies all patients without the disease.A test with 80% specificity correctly reports 80% of patients without the disease as testnegative (true negatives) but 20% patients without the disease are incorrectly identified astest positive (false positives).As discussed above, a test with a high sensitivity but low specificity results in manypatients who are disease free being told of the possibility that they have the disease and arethen subject to further investigation. Although the ideal (but unrealistic) situation is for a100% accurate test, a good alternative is to subject patients who are initially positive to atest with high sensitivity/low specificity, to a second test with low sensitivity/high specificity.In this way, nearly all of the false positives may be correctly identified as disease negative.

Positive predictive valueThe PPV of a test is a proportion that is useful to clinicians since it answers the question:‘How likely is it that this patient has the disease given that the test result is positive?’Positive predictive value =True positives True positives + False positivesNegative predictive valueThe NPV of a test answers the question: ‘How likely is it that this patient does not have the disease given that the test result is negative?’Negative predictive value = True negatives True negatives + False negatives

Cell adhesion

Cell adhesion is essential for the development and maintenance of multicellular organisms. Cell-cell and cell-matrix contacts facilitate intercellular communication and define the architecture of

organs. The regulated nature of cell adhesion is particularly evident in the hematopoietic system, where cells routinely make transitions between nonadherent and adherent phenotypes during differentiation and in response to stimuli in the circulation or extravascular tissues.In the bone marrow, proliferation and differentiation of hematopoietic stem cells is controlled not only by soluble growth factors, but also by adhesion to stromal cells and matrix molecules. Weakening of these adhesive bonds is required for mature blood cells to enter the circulation. Circulating erythrocytes normally remain nonadhesive until they are finally cleared by the reticuloendothelial system. Other circulating cells often participate in regulated adhesive events during their life span.For example, prothymocytes adhere to components of the thymus, where they undergo further maturation before reentering the circulation. Lymphocytes regularly stick to the specialized high endothelial venules of lymphoid tissues, migrate into these tissues for sampling of processed antigens, and then exit via the lymphatics.During inflammation, specific classes of leukocytes roll on the endothelium, then adhere more tightly, and finally emigrate between endothelial cells into the tissues.There, neutrophils and monocytes phagocytose invading pathogens, whereas lymphocytes adhere to antigen-presenting macrophages. During hemorrhage, platelets stick to exposed subendothelial matrix components, spread, and recruit additional platelets into large aggregates that serve as an efficient surface for thrombin and fibrin generation. Leukocytes also adhere to activated platelets, a mechanism for linking hemostatic and inflammatory responses. The endothelial cells expressmolecules that affect the adhesiveness of platelets or leukocytes. Tight contacts between adjacent endothelial cells also limit access of blood cells to the underlying tissues.ADHESION MOLECULESCells adhere through noncovalent bond formation between macromolecules on cell surfaces with macromolecules on other cell surfaces or in extracellular matrix.These interactions involve either protein-protein or protein-carbohydrate recognition. Although some adhesion molecules are expressed only by blood or endothelialcells, most are also synthesized by other cells. Many adhesion molecules can be grouped into families according to related structural and functional features.

FACTORS DETERMINING HAZARD POTENTIAL

Although most chemicals have a toxic potential, the extent to which they pose a hazard to health will depend on the interplay between a number of factors.

The physical state of the chemical:

Chemical substances may exist as a single phase medium such as a solid, liquid or gas, or coexist in more than one form. Solids can give off hazardous gases or vapours, be changed to fumes by burning or melting (e.g. heavy metals) or be changed to airborne dusts by grinding, cutting or abrasion. Dispersed in the air they are easily inhaled and are able to exert their toxic effects. Lipid soluble liquids (e.g. phenol, aniline) are easily absorbed through the skin. Liquids can be dispersed as mists or give off vapours by industrial processes and in this way become airborne.

The route of exposure of the chemical

Chemical substances can enter the body through inhalation, which is by far the most common route of entry for a large number of chemicals. Absorption through the skin or via the eyes occurs either through direct skin contact or from contact with contaminated surfaces or clothing. Chemical ingestion in the workplace may occur

either by chemicals settling directly on food or workers eating food with contaminated fingers.

The exposure dose of the chemical

The most important environmental factors determining exposure dose include the concentration, duration and frequency of exposure to the chemical concerned. Certain chemicals such as sensitisers and irritants may produce adverse local health effects from single episodes of exposure to very high concentrations of the substance. Other chemicals such as solvents and heavy metals exert their systemic health effects as a result of repeated low dose exposure to these chemicals. The presence of administrative controls such as job rotation, use of personal protective equipment and engineering controls (e.g. local exhaust ventilation) may also modify the exposure dose.

Individual differences among exposed individuals

There are a number of host factors that determine the extent to which chemicals are absorbed, distributed, metabolised and excreted by the body. Individual physical characteristics such as physical work load (e.g. heavy manual work underground) and skin characteristics (e.g. presence of pre-existing eczema) can increase the amount of chemical absorbed by the body. Furthermore, dietary patterns can also increase the amount of chemicals absorbed due to chemical contamination of the food chain (e.g. arsenic in fish), making it difficult to differentiate between occupational exposure and general background environmental exposure. The body size and composition (fat content) are particularly important since they determine the potential surface area available for distribution and deposition of the chemical in various parts of the body. Certain solvents (e.g. benzene) have a high affinity for fat deposition and result in increased blood levels even after exposure has ceased. There are various factors such as age, gender, and social habits that modify the manner in which the chemical is metabolised and excreted by the body. Social habits such as smoking tobacco and alcohol consumption increase the absorption and the metabolism of chemicals such as lead. Pre-existing kidney disease and old age are associated with decreased excretion of the chemical, thereby increasing the concentration of heavy metals (e.g. mercury, cadmium and lead) in the body to exert their toxic effects.

FATE OF CHEMICALS ENTERING THE BODY:

Once the chemical enters the body, it is transported by blood to organs, such as the liver, where it is converted through various metabolic processes into a less toxic (or occasionally a more toxic) water-soluble metabolite before being excreted via the kidneys and/or liver. The rate at which substances are absorbed into the body and the rate at which they are distributed to different tissues, metabolised and excreted, can differ markedly between substances.

The biological half-life (t½) of a substance or its metabolite is the time taken for its concentration to fall to 50% of its original value after the end of exposure. Half-life can be measured in minutes, hours or days. Some chemical substances have a shorter biological half-life and a shorter residence time within which to exert their toxic effects e.g. benzene,

carbon monoxide. Other substances have low excretion rates, a long biological half-life and may therefore persist in body tissues for a long period of time (months or years) causing chronic ill-health e.g. lead, mercury. It is this dose fraction of the chemical that enters and persists in the tissue of the target organ that causes impaired functioning and the manifestation of clinical disease. Biological monitoring procedures are designed to detect the presence of these absorbed substances in body fluids such blood/plasma and urine.

Antigens stimulate an immune response

An antigen is any substance to which the immune system can respond. For example, components of the bacterial cell wall can trigger severe and immediate attacks by neutrophils.

If the immune system encounters an antigen that is not found on the body's own cells, it will launch an attack against that antigen. Conversely, antigens that are found on the body's own cells are known as "self-antigens", and the immune system does not normally attack these.

The membrane of each red blood cell contains millions of antigens that are ignored by the immune system. However, when patients receive blood transfusions, their immune systems will attack any donor red blood cells that contain antigens that differ from their self-antigens. Therefore, ensuring that the antigens of transfused red blood cells match those of the patient's red blood cells is essential for a safe blood transfusion.

IntroductionThe Latin term “immunis” meaning “exempt” gave rise to the English word “immunity”, which refers to the mechanisms used by the body to protect against environmental agents that are foreign to the body. These agents may be microorganisms or their products, foods, chemicals, drugs, pollen or animal hair.InfectionsThe invasion and multiplication of a parasite in or on the surface of host tissue constitute infection. Infection and immunity involve interaction between the body (host) and the infecting microorganism. Based on their relationship to their host, microorganismsclassified as saprophytes (free living microbes that subsist on dead or decaying organic matter, mostly found in soil). Parasites (establish themselves and multiply in hosts ( it may be pathogens - disease producing) or commensals (without causing any damage to the host-normal flora).Infections may be classified in various ways.Primary infection : First time infection with a parasite in a host.Secondary infection : When new parasite sets up an infection in a host whose resistance is lowered by a preexisting infectious disease.Focal infection : Infection or sepsis at localized sites (tonsils).Cross infection : When a patient already suffering from a disease a new infection is set up from another host or another external source.Reinfections : Subsequent infections by the same parasite in the host.Nosocomial infections : Cross infection occurring in hospitals .

Latent infection : Some parasites, following infection, may remain in the tissues in a latent or hidden form, multiply and producing clinical disease whenthe host resistance is lowered.Sources of infection : Many pathogens are able to infect, which may be from1. Human beings to human beings, or from animals to human beings(Zoonotic disease eg – Plague).2. From insects to human beings (arthropod borne disease eg Malaria).3. From soil, water and contaminated food. This may enter the host by either, direct contact (contagious disease) or indirect (like clothing).It may also occur byi) Inhalation of pathogen (Influenza)ii) Ingestion of food or drinks contaminated by pathogensiii) Inoculation directly into the tissues of the host (Tetanus spores).iv) Congenitally some pathogens (eg) rubella virus) are able to cross the placental barrier and infect the fetus in utero (Vertical transmission).Infectious disease may be localized ( superficial or deep-seated) or generalized (spreading through tissue spaces and circulation). However,it can be Endemic (when a small number of cases occur constantly among the population of a community eg: Typhoid), Epidemic (The disease flares up and large number of cases develop with in a community with in a shorttime. eg: Influenza) or Pandemic ( when an epidemic becomes very widespread areas in the world involving large number of people with in a short period).BacteriaBacteria are unicellular prokaryotic organisms.Based on the structure and shape three major group of bacteria namely, Bacillus (cylindrical forms), Coccus (spherical forms) and Spiral. Humans and animals have abundant normal flora (microbes) that usually do not producedisease under normal healthy condition. The pathogenesis of bacterial infection includes initiation of the infectious process and mechanisms that lead to the development of signs and symptoms of disease. Many bacterial infections are considered pathogenic, though they are unapparent or asymptomatic.Viral infectionsVirus are acellular obligate intracellular parasites. It contain only one type of nucleic acid, it may be either single or double stranded DNA or RNA. The extracellular infectious virus particle is called the virion. The virion consists of nucleic acid surrounded by a protein coat called capsid which protects the nucleic acid from deleterious environment and tointroduce viral genome into the host cells by adsorbing readily to the cell surface.Pathogenesis of viral infectionViral diseases range from minor ailments such as the common cold to terrifying diseases such as Rabies and Acquired Immune Deficiency Syndrome (AIDS). They may be sporadic like Mumps, endemic like Infectious hepatitis, epidemic like Dengue fever or pandemic like Influenza.Depending on the clinical outcome, viral infections can be classified as unapparent (sub clinical) or apparent (Clinical or overt) infections.FungiFungi are eukaryotic protista, recognized as causative agents of human disease earlier than bacteria. Fungi possess rigid cell wall containing chitin, mannose and other polysaccharides. They divide asexually, sexually or by both processes. They may be unicellular or multicellular.

Depending on the cell morphology fungi can be divided into four classesi)Yeasts : Unicellular fungi which occur as spherical and reproduce by simple buddingii) Yeast like fungi : Grow partly as yeast and partly as elongated cells resembling hyphae form a pseudo myceliumiii) Moulds : True mycelia and they are reproduced by the formation of different types of spores.iv) Dimorphic fungi : Occur as filaments (soil) or as yeasts (host tissues) depending on the conditions of growth.Human fungal infections are usually of two types superficial and deep seated. Fungi causing superficial mycoses are specialized saprophytes, with the capacity to digest keratin. Superficial mycoses are of two types - surface infections (only on dead layers of skin) and

cutaneous infections (cornified layer).

ImmunityDisease spreads from one person to another is called as infectious disease. Infectious diseases are caused by foreign substances like fungi, bacteria, virus or parasite, when they enter in to the human body. Though the disease by such pathogen affects the body for a shorter duration, the person may survive after loosing functions of some of the organ (eg. Poliomyelitis). Some times, when the infection or disease is severe the person has to die. Yet many of the human beings are able to lead a normal life because of the immune system. The immune system provides such freedom enjoyed by an individual, in order to keep them free from diseases.The immune system has the following the functions, 1. Recognition and defense against foreign substances (antigen) irrespective of the route of entry.2. Depending upon the nature of the pathogen, appropriate immune reaction is mounted.3. The antigen induced Antibody combine specifically to that antigen (Specificity)4. Immune system keep memory about the pathogens and when the same pathogen reenters a better immune response is produced. This forms the basis of vaccination.5. Recognition and destruction of the mutant cells that can become cancerous and this is know as Immunosurveillance.6. Normally, Immune system does not produce antibodies against its own body tissues (self antigens), called as Immune tolerance or Self recognization.Depending on the nature of response towards the pathogen, Immune system is broadly classified into Natural and Acquired immunity.

Immune system is classified as follows.

Natural ImmunityThe non specific immunity present from birth is known as innate immunity or natural immunity. It protects the body against any foreign invaders and does not show any specificity. It is also functionally matured in a new born. It does not become more efficient after subsequent exposures to same organism.InflammationA localized protective reaction produced in tissue response to any irritation, injury or infection is called as inflammation. This is characterized by pain, redness, swelling, and sometimes loss of function.

Usually, the name of the tissue, organ and the region which develops inflammation is suffixed with ‘itis’ for example conjunctivitis, gastritis and pharyngitis respectively. The inflammatory response helps to mobilize the nonspecific defense forces to the tissue space where pathogen is present.The damaged cells release chemical mediators such as histamine from the mast cells, which dilate the near by blood vessels. The complement system gets activated and attracts phagocytes. The plasma leaking from the dilated blood vessel contains clotting system of proteins. They get activated due to the tissue damage and this process leads to “walling off” the area and this helps to prevent spreading of the infectious material.

Antibiotic Resistance DetectionThe resistance of widespread Gram-positive and Gram-negative bacteria against antibiotics is a severe and growing issue in healthcare. Infections caused by resistant microorganisms often fail to respond to conventional treatment, resulting in prolonged illness, greater risk of death, and higher costs. A high percentage of hospital-acquired infections are caused by highly resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) or multidrug-resistant Gram-negative bacteria. In the European Union, about 25 000 patients die eachyear from infections caused by selectedmultidrug-resistant bacteria and the associatedcosts are estimated at about 1.5 billion Euros per year. In the United States of America, infections with pathogens resistant to antimicrobials cost the healthcare system in excess of US$ 20 billion annually and generate more than 8 million additional hospital days.The annual societal costs exceed US$ 35 billion . In order to tackle these challenges, a large number of DNA microarray tests have been developed in recent years . A few microarrays weredeveloped that cover both Gram-positive and Gram-negative organisms. A broad, high-density microarray, which enabled the identification of 775 genes encoding resistance to aminoglycosides, beta-lactams, chloramphenicols, glycopeptides, heavy metals, lincosamides, macrolides, metronidazoles, polyketides, quaternary ammonium compounds, streptogramins, sulfonamides, tetracyclines, and trimethoprims as well as resistance transfer genes of Gram-negative and Gram-positive bacteria, was developed by Frye et al. [43]. This microarray covered virtually all antibiotic resistance genes found in the National Centrefor Biotechnology Information (NCBI) database, thus reducing the subsequent assays necessary to identify specific resistance gene alleles. This microarray was intended to be used as a screening technique in studies of prevalence, epidemiology, and spread of resistance genes. It was built on an earlier version of a microarray with long 70-mer probes in order to cover all allelic variations of the corresponding resistance gene. This initial version, which was developed by the same group in 2006, covered 94 resistance genes.

URINALYSISThe urinalysis is another common test routinely taken in almost all acute hospitals as an admission lab screening test. It can easily reveal renal and systemic pathologies. Everyone should be reminded of the importance of this test. It has become such a routine patient test, that often, care is not taken when collecting and handling specimens. This improper handling can affect the results of the test, since contamination can occur at any point in the handling.Even the routine urinalysis should be a midstream specimen after cleansing the meatus. This does not require any special equipment or expense to the patient.

Some hospitals will require that even the routine urinalysis be collected under sterile conditions just as a culture specimen would be collected. The container for this routine specimen should be clean; again, in some cases, the hospital requires a sterile container for all specimens. Remember that it will always save time in the long run to take care not to contaminate any type urine specimen.