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CLINICAL ENZYMOLOGY

CLINICAL ENZYMOLOGY. Measurements of the activity of enzymes in plasma are of value in the diagnosis and management of a wide variety of diseases.

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CLINICAL ENZYMOLOGY

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  1. CLINICAL ENZYMOLOGY

  2. Measurements of the activity of enzymes in plasma are of value in the diagnosis and management of a wide variety of diseases.

  3. Small amounts of intracellular enzymes are present in the blood as a result of normal cell turnover. When damage to cells occurs, increased amounts of enzymes will be released and their concentrations in the blood will rise.

  4. However, such increases are not always due to tissue damage. • Other possible causes include: • increased cell turnover • cellular proliferation (e.g. neoplasia) • increased enzyme synthesis (enzyme induction) • obstruction to secretion

  5. Enzyme activity • Enzyme assays usually depend on the measurement the catalytic activity of the enzyme, rather than the concentration of the enzyme protein itself.

  6. One international unit is the amount of enzyme that will convert one micromole of substrate per minute per litre of sample and is abbreviated as U/L. • Katal (catalytic activity) is defined as the number of mole of substrate transformed per second per litre of sample.

  7. Disadvantages of enzyme assays • A major disadvantage in the use of enzymes for the diagnosis of tissue damage is their lack of specificity to a particular tissue or cell type. Many enzymes are common to more than one tissue.

  8. This problem may be obviated to some extent in two ways: • first, different tissues may contain (and thus release when they are damaged) two or more enzymes in different proportions

  9. Second, some enzymes exist in different forms (isoforms) • Individual isoforms are often characteristic of a particular tissue: although they may have similar catalytic activities

  10. Alkaline phosphatase (ALP) • Normal serum level of ALP is 40-125 U/L or 0.5-1.3 mmol/(hourL). • This enzyme present in high concentrations in the • liver • bone (osteoblasts) • placenta • intestinal epithelium.

  11. The causes of an increase in plasma ALP activity • Physiological increases are been in pregnancy, due to the placental isoenzyme, and in childhood (when bones are growing), due to the bone isoenzyme.

  12. Pathological: often >5 x ULN • Paget's disease or bone osteomalacia • rickets • cholestasis (intra- and extrahepatic) • cirrhosis • usually <5 x ULN • bone tumours (primary and secondary), • primary hyperparathyroidism with bone involvement, healing fractures, • Osteomyelitis • hepatic space-occupying lesions (tumour, abscess)

  13. ACID PHOSPHATASE (ACP) • It hydrolyses phosphoric acid ester at pH between 4 and 6. • ACP is secreted by prostate cells, RBC, platelets and WBC. • Normal serum value for ACP is 2.5-12 U/L or 0.025-0.12 mmol/(hourL).

  14. ACP total value is increased in prostate cancer and highly elevated in bone metastasis of prostate cancer. • ACP is therefore an important tumour marker. • ACP is present in high concentration in semen, a finding which is used in forensic medicine in investigation of rape.

  15. Aminotransferases • Two aminotransferases are used in diagnosis and management: aspartate aminotransferase (AST) • and alanine aminotransferase (ALT).

  16. ASPARTATE AMINO TRANSFERASE (AST) • It is also called as serum glutamate-oxaloacetate transaminase (SGOT). • Normal serum level of AST is 8- 40 U/Lor (0.1-0.45 mmol/(hourL)) • It is significantly elevated in myocardial infarction. It if moderately elevated in liver diseases.

  17. Measurement of cardiac enzyme levels • Measure cardiac enzyme levels at regular intervals, starting on admission and continuing until the peak is reached or until 3 sets of results are negative. Biochemical biomarkers are useful for both diagnosis and prognostication

  18. Laboratory Diagnosis of Myocardial Infarction

  19. ALANINE AMINO TRANSFERASE (ALT) • It is also called as serum glutamate-pyruvate transaminase (SGPT). • Normal serum level of ALT is 5-30 U/L or (0.1-0.68 mmol/(hourL))

  20. Very high values (100 to 1000 U/L) are seen in acute hepatitis, either toxic or viral in origin. • Both ALT and AST are increased in liver diseases, but ALT >AST. • Moderate increase (25 to 100 U/L) may be seen in chronic liver disease such as cirrhosis, and malignancy in liver.

  21. Ritis coefficient (AST/ALT) in normal conditions is • 1.33±0,42.

  22. LACTATE DEHYDROGENASE (LDH) (LD) • Normal value of LDH in serum is 100-200 U/L. • Values the upper range are generally seen in children. Strenuous exercise will slightly increase the value. LDH level is 100 times more inside the RBC than in plasma, and therefore minor amount of hemolysis will result in a false-positive test.

  23. This enzyme exists in body tissues as a tetramer. Two monomers, H and M, can combine in various proportions with the result that five isoenymes of LD are known. • So five combinations of H and M chains are possible; H4, H3M, H2M2, M3H and M4

  24. The iso-enzymes are usually separated by cellulose acetate electrophoresis at pH 8.6. • Lactate dehydrogenase isoenzymes (as percentage of total): • LDH1 14-26 % • LDH2 29-39 % • LDH3 20-26 % • LDH4 8-16% • LDH5 6-16 %

  25. Increase in total LDH level is seen in • hemolytic anemias, • hepatocellular damage, • muscular dystrophy, • carcinomas, • leukemias, • and any condition which causes necrosis of body cells.

  26. Creatine kinase (CK) • Normal serum value for CK is 15-100 U/L for males and 10-80 U/L for females. • CK is a dimer; each subunit has a molecular weight of 40,000. The subunits are called B for brain and M for muscle.Three isoenzymes, BB, MM and MB, occur. • Normally CK2 (MB) iso-enzyme is only 5% of the total activity.

  27. Causes of an increased plasma creatine kinase activity. • often >10x ULN • polymyositis • rhabdomyolysis (e.g. trauma, malignant hyperpyrexia) • Duchenne muscular dystrophy • myocardial infarction • 5-10 x ULN • following surgery • skeletal muscle trauma • severe exercise • myositis • carriers of Duchenne muscular dystrophy • usually <5 x ULN • physiological (Afro-Caribbeans) • hypothyroidism • drug (statin) treatment

  28. NUCLEOTIDE PHOSPHATASE (NTP) • It is a marker enzyme for plasma membranes and is seen as an ecto-enzyme (enzyme present on the cell membrane). • Normal NTP level in serum is 2-10 U/L. It is moderately increased in hepatitis and highly elevated in biliary obstruction.

  29. GAMMA GLUTAMYL TRANSFERASE (GGT) • It is seen in liver, kidney, pancreas, intestinal cells and prostate gland. • In the body it is used in the synthesis of glutathione. • Normal serum value of GGT is 6-45 U/L in male and 5-30 U/L in female.

  30. This value is moderately increased in infective hepatitis and prostate cancers. The GGT level is highly elevated in alcoholism, obstructive jaundice and neoplasm's of liver.

  31. PROSTATE SPECIFIC ANTIGEN (PSA) • It is produced from the secretory epithelium of prostal gland. It is normally secreted into seminal fluid • Normal value is 1 -5 µg/L. It is very specific for prostate activity. Values between 4-10 µg/L is seen in benign prostate enlargement; but values above 10 µg/L is indicative of prostate cancer.

  32. CHOLINESTERASE (ChE) • This enzyme is secreted by the liver into the blood- stream and low plasma activities occur in chronic hepatic dysfunction. Low activities occur physiologically during pregnancy.

  33. Interest in this enzyme derives largely from the fact that it hydrolyzes a muscle-relaxant drug, widely used in anaesthesia, called succinylcholine (scoline). Occasionally, patients are found in whom the effect of this drug, which paralyzes respiration, persists for several hours after it has been administered (scoline apnoea). Many of these patients have an abnormal cholinesterase activity.

  34. CHOLINESTERASE (ChE) • Acetyl cholinesterase or true ChE or Type 1 ChE can act mainly on acetyl choline. Normal serum range is 2-12 U/ml • It is present in nerve endings and in RBCs. • Plasma cholinesterase activity also falls in organophosphate poisoning. • Organophosphorus insecticides (Parathione) irreversibly inhibit ChE in RBCs. Measurement of ChE level in RBCs is useful to determine the amount of exposure in persons working with these insecticides.

  35. Pseudocholinesterase or type II ChE is non-specific and can hydrolyse acyl esters. It is produced mainly by liver cells. Normal serum level is 8-18 U/ml.

  36. GLUCOSE-6-PHOSPHATE DEHYDROGENASE • This is an important enzyme in the hexose monophosphate shunt pathway of glucose. • Normal value of GPD in RBC is 125-250 U/1012 cells. • It is mainly used for production of NADPH. It has a special role in the RBC metabolism.

  37. AMYLASE • This splits starch to maltose. It is activated by calcium, chloride and fluoride ions. • It is produced by pancreas and salivary glands • Normal serum value is 50-120 U/L, (12-32 g/(hour× L)).

  38. The value is increased about 1000 times in acute pancreatitis which is a life-threatening condition. The peak values are seen between 5-12 hours after the onset of disease and returns to normal levels within 2-4 days after the acute phase has subsided.

  39. Moderate increase in serum levels are seen in chronic pancreatitis, mumps (parotitis), obstruction of pancreatic duct and in renal disease. • Normal urine value is 20-160 g/(hour× L) or (less than 375 U/L). • It is increased in acute pancreatitis. It is increased on the 1 st day and remains to be elevated for 7-10 days.

  40. LIPASE • It will hydrolyse triglyceride to β-monoglyceride and fatty acid. • The enzyme is present in pancreatic secretion. • Normal serum range is 0.2-1.5 U/L.

  41. It is highly elevated in acute pancreatitis and this persists for 7-14 days. Thus, lipase remains elevated longer than amylase. • Moreover, lipase is not increased in mumps.

  42. Aldolase (ALD) • It is a tetrameric enzyme with A and B subunits; so there are 5 iso-enzymes. It is a glycolytic enzyme. • Normal range of serum is 1.5-7 U/L. • It is drastically elevated in muscle damages such as progressive muscular dystrophy, poliomyelitis, myasthenia gravis and multiple sclerosis.

  43. Enolase • It is a glycolytic enzyme. Neuron-specific enolase (NSE) is an iso-enzyme seen in neural tissues and Apudomas. NSE is a tumour marker for cancers associated with neuro-endocrine origin, small cell lung cancer,neuroblastoma,pheochromocytom, medullary carcinoma of thyroid, etc. • Upper limit of NSE is 12 μg/ml.

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