The use of The use of

LABORATORY LABORATORY ANALYSIS clinical ANALYSIS clinical

practicepractice

Clinical Laboratory diagnostics(laboratory medicine) is

the medical discipline devoted to obtain, explore and employ knowledge about using various techniques for the analysis of body fluids composition and properties of cells and tissues, and interpretation of the results in relation to health and disease.

The results of laboratory tests may The results of laboratory tests may be of use in:be of use in:

diagnosis and in the monitoring of diagnosis and in the monitoring of treatment. treatment.

screening for disease screening for disease in assesing the prognosis in assesing the prognosis reseach into the biochemical basis of reseach into the biochemical basis of

disease disease clinical trials of new drugsclinical trials of new drugs

Biochemical tests can be broadly Biochemical tests can be broadly divided into two groups: divided into two groups:

In In 1. 1. discretionary or selective discretionary or selective requestingrequesting,, the tests are carried out the tests are carried out on the basis of an individual patient's on the basis of an individual patient's clinical situation. clinical situation.

In contrast, In contrast, 2. 2. screening testsscreening tests are are used to search for disease without used to search for disease without there being any necessary clinical there being any necessary clinical indication that disease is present.indication that disease is present.

Test selection for the purposes Test selection for the purposes of discretionary testingof discretionary testing

To confirm a diagnosis - To confirm a diagnosis - Plasma (free Plasma (free T4) and (thyroid-stimulating T4) and (thyroid-stimulating hormone, TSH) in suspected hormone, TSH) in suspected hyperthyroidismhyperthyroidism

To aid differential diagnosis - To aid differential diagnosis - To To distinguish between different forms distinguish between different forms of jaundiceof jaundice

To monitor progress - To monitor progress - Plasma Plasma (glucose) to follow of patients with (glucose) to follow of patients with diabetes mellitusdiabetes mellitus

ScreeningScreening may take two forms: may take two forms:

1.1. Well-population screeningWell-population screening in in which typically a spectrum of tests is which typically a spectrum of tests is carried out on individuals from an carried out on individuals from an apparently healthy population in an apparently healthy population in an attempt to detect presymptomatic or attempt to detect presymptomatic or early disease. early disease.

2. Case-finding screening2. Case-finding screening programmes perform programmes perform appropriate tests on a population appropriate tests on a population sample known to be at high risk sample known to be at high risk of a particular disease.of a particular disease.

NeonatesNeonates:: PKAPKA (phenylketonuria) (phenylketonuria) - Serum - Serum

[phenylalanine][phenylalanine] HypothyroidismHypothyroidism - - Serum [TSH] and/or Serum [TSH] and/or

[thyroxine][thyroxine]

PregnancyPregnancy:: Diabetes mellitus in the motherDiabetes mellitus in the mother - -

Plasma and urine [glucose] Plasma and urine [glucose] Open neural tube defect (NTD) in the Open neural tube defect (NTD) in the

foetusfoetus - Maternal serum [a-fetoprotein] - Maternal serum [a-fetoprotein]

Core biochemistry:Core biochemistry:

Most biochemistry laboratories Most biochemistry laboratories provide the "core analyses", provide the "core analyses", commonly requested tests which commonly requested tests which are of value in many patients, on are of value in many patients, on a frequent basis.a frequent basis.

Core biochemical tests:Core biochemical tests: 1. Sodium, potassium, chloride and 1. Sodium, potassium, chloride and

bicarbonatebicarbonate 2. Urea and creatinine2. Urea and creatinine 3. Calcium and phosphate3. Calcium and phosphate 4. Total protein and albumin4. Total protein and albumin 5. Bilirubin and alkaline phosphatase5. Bilirubin and alkaline phosphatase 6. Alanine aminotransferase (ALT) and 6. Alanine aminotransferase (ALT) and

Aspartate aminotransferase (AST)Aspartate aminotransferase (AST) 7. Glucose7. Glucose 8. Amylase8. Amylase

Specialized tests:Specialized tests: Not every laboratory is equiped to Not every laboratory is equiped to

carry out all possible biochemistry carry out all possible biochemistry requests.requests.

1. Hormones1. Hormones 2. Specific proteins2. Specific proteins 3. Trace elements3. Trace elements 4. Vitamins4. Vitamins 5. Drugs5. Drugs 6. Lipids and lipoproteins6. Lipids and lipoproteins 7. DNA analyses7. DNA analyses

The emergency tests:The emergency tests: All clinical biochemistry laboratories All clinical biochemistry laboratories

provide facilities for urgent tests. An provide facilities for urgent tests. An urgent test is designated as one on which urgent test is designated as one on which the clinician is likely to take immediate the clinician is likely to take immediate action. action.

1. Urea and electrolytes1. Urea and electrolytes 2. Blood gases2. Blood gases 3. Amylase3. Amylase 4. Glucose4. Glucose 5. Salicylate5. Salicylate 6. Paracetamol6. Paracetamol 7. Calcium7. Calcium

TheThe biological fluidsbiological fluids employed employed in the clinical biochemistry in the clinical biochemistry laboratory includelaboratory include

blood, urine, saliva,blood, urine, saliva, sputum, sputum, faeces, tissue and cells,faeces, tissue and cells, cerebrospinal fluidcerebrospinal fluid, , peritoneal fluid,peritoneal fluid, synovial synovial fluid, pleural fluid,fluid, pleural fluid, stones.stones.

COLLECTION OF BLOOD:COLLECTION OF BLOOD: VenousVenous bloodblood is most commonly is most commonly

used for a majority of biochemical used for a majority of biochemical investigations. It can be drawn from investigations. It can be drawn from any prominent vein (usually from a any prominent vein (usually from a vein on the front of the elbow).vein on the front of the elbow).

Capillary bloodCapillary blood (<0.2 ml) obtained (<0.2 ml) obtained from a finger or thumb, is less from a finger or thumb, is less frequently employed.frequently employed.

Arterial bloodArterial blood ( (usually drawn under usually drawn under local anesthesia) is used for blood local anesthesia) is used for blood gas determinations.gas determinations.

Biochemical investigations Biochemical investigations can be performedcan be performed on 4 on 4 types of blood specimenstypes of blood specimens ––

whole blood, plasma, serum whole blood, plasma, serum and red blood cells.and red blood cells.

11. . Whole bloodWhole blood (usually (usually mixed with an anticoagulant) mixed with an anticoagulant) is used for the estimation ofis used for the estimation of

hemoglobin, hemoglobin, carboxyhemoglobin, pH, carboxyhemoglobin, pH, glucose, urea, non-protein glucose, urea, non-protein nitrogen, pyruvate, lactate, nitrogen, pyruvate, lactate, ammonia etc. ammonia etc.

2. Plasma2. Plasma,, obtained by obtained by centrifuging the whole blood centrifuging the whole blood collected with an collected with an anticoagulant, is employed anticoagulant, is employed for the parameters —for the parameters —

fibrinogen, glucose, fibrinogen, glucose, bicarbonate, chloride, bicarbonate, chloride, ascorbic acid etc.ascorbic acid etc.

3. Serum3. Serum is the supernatant fluid is the supernatant fluid that can be collected after that can be collected after centrifuging the clotted blood. centrifuging the clotted blood.

The parameters estimated in The parameters estimated in serum include proteins serum include proteins (albumin/globulins), creatinine, (albumin/globulins), creatinine, bilirubin, cholesterol, uric acid, bilirubin, cholesterol, uric acid, electroylets (Na+, K+, Cl-), electroylets (Na+, K+, Cl-), enzymes (ALT, AST, LDH, CK, ALP, enzymes (ALT, AST, LDH, CK, ALP, ACP, amylase, lipase) and vitamins.ACP, amylase, lipase) and vitamins.

4. Red blood cells4. Red blood cells are are employed for the employed for the determination of abnormal determination of abnormal hemoglobins, glucose 6-hemoglobins, glucose 6-phosphate dehydrogenase, phosphate dehydrogenase, pyruvate kinase etc.pyruvate kinase etc.

ANTICOAGULANTSANTICOAGULANTS

1. Heparin1. Heparin (inhibits the (inhibits the convension prothrmobin to convension prothrmobin to

thrombin) is the most widely thrombin) is the most widely used anticoagulant for clinical used anticoagulant for clinical

chemical analysis. Heparin is an chemical analysis. Heparin is an ideal anticoagulant, since it does ideal anticoagulant, since it does

not cause any change in blood not cause any change in blood composition. composition.

Ethylene diamine tetra acetic Ethylene diamine tetra acetic acid (EDTA)acid (EDTA) is a chelating is a chelating agent, and is particularly useful agent, and is particularly useful for hematological examination for hematological examination because it preserves cellular because it preserves cellular components of the BLOOD. components of the BLOOD.

3. Sodium3. Sodium fluoridefluoride is usually is usually used as a preservative for blood used as a preservative for blood glucose by inhibiting the enzyme glucose by inhibiting the enzyme systems involved in the systems involved in the glycolysis. glycolysis.

It should not be used for enzyme It should not be used for enzyme assays, as well as when the test assays, as well as when the test involves enzymatic analysis.involves enzymatic analysis.

COLLECTION OF URINE:COLLECTION OF URINE: For biochemical investigations, urine For biochemical investigations, urine

can be collected as a single can be collected as a single specimen or for 24 hours. Single specimen or for 24 hours. Single specimens of urine, normally specimens of urine, normally collected in the morning, are useful collected in the morning, are useful for qualitative tests e.g., sugar, for qualitative tests e.g., sugar, proteins. proteins.

Urine specimens tend to deteriorate.Urine specimens tend to deteriorate.

The changes include:The changes include: 1. destruction of glucose by bacteria;1. destruction of glucose by bacteria; 2. conversion of urea to ammonia, by 2. conversion of urea to ammonia, by

bacte ria, with fall in [H+] and bacte ria, with fall in [H+] and precipitation of phosphates;precipitation of phosphates;

3. oxidation of urobilinogen to 3. oxidation of urobilinogen to urobilin and porphobilinogen to urobilin and porphobilinogen to porphyrins.porphyrins.

Preservatives for urine :Preservatives for urine : The The preservatives are used (1) to reduce preservatives are used (1) to reduce bacterial action; (2) to minimise bacterial action; (2) to minimise chemical decomposition, and (3) to chemical decomposition, and (3) to decrease atmospheric oxidation of decrease atmospheric oxidation of unstable compounds. unstable compounds.

Formalin, thymol, chloroform, Formalin, thymol, chloroform, toluene, concentrated HCI and glacial toluene, concentrated HCI and glacial acetic acid are the commonly used acetic acid are the commonly used urine preservatives.urine preservatives.

Biological factors affecting Biological factors affecting the interpretation of the interpretation of

results:results: Sex of the patient. Sex of the patient. Age of the patient. Age of the patient. Effect of dietEffect of diet Time when sample was taken.Time when sample was taken. Stress and anxiety. Stress and anxiety. Posture of the patient. Posture of the patient. Effects of exercise. Effects of exercise. Medical history. Medical history. Pregnancy. Pregnancy. Menstrual cycle. Menstrual cycle. Drug history. Drug history.