Diagnostic Enzymology PDF

Diagnostic Enzymology Dr.Abrar Albadr M.B.Ch.B FIBMS (Chem.Pathology) Clinical Scenario 21-year-old male presented complaining of fever, vomiting and abdominal tenderness in the right upper quadrant. On examination , the doctor found that he was pyrexial and jaundiced. The liver w...

Diagnostic Enzymology Dr.Abrar Albadr M.B.Ch.B FIBMS (Chem.Pathology) Clinical Scenario 21-year-old male presented complaining of fever, vomiting and abdominal tenderness in the right upper quadrant. On examination , the doctor found that he was pyrexial and jaundiced. The liver was enlarged and tender. Investigations revealed: Serum Result Reference range ALP activity 190 40–125 U/L ALT activity 560 10–50 U/L GGT activity 60 5–35 U/L Comment on these results. What is the most likely diagnosis?  Enzymology Enzymology can be defined as the assay of an enzyme(s) in body fluids, usually blood, that can be used diagnostically or to monitor a clinical condition. It has limitations, as generally plasma enzyme activity lacks specificity. Isoenzyme(molecular variants of enzymes) determination or measuring a number of enzymes may increase diagnostic accuracy.  Enzymes Functional plasma Non-functional enzymes plasma enzymes Present at all times in the No specific function in circulation and perform a the plasma but function physiological function in the within the cell blood Released from cells during normal cell turnover e.g lipoprotein lipase , pseudocholinestrase Very low level in the serum Levels rise in serum during tissue injury Help to diagnose the site and extent of tissue injury e.g LDH Normally, plasma enzyme activity represents Steady state The rate of enzyme entry into plasma = The rate of enzyme removal from plasma Enzyme activity in plasma may be : Higher than normal Lower than normal 1 Due to the proliferation of cells, 2 Due to reduced synthesis, an increase in the rate of cell congenital deficiency or the turnover or damage or in presence of inherited enzyme synthesis (induction), variants of relatively low or to reduced clearance from biological activity. plasma. Sometimes macroenzymes are found, it is a high-molecular- weight form of a native enzyme. Often these are enzymes complexed with immunoglobulins and are more common in individuals with autoimmune disease.  Clinically important plasma enzymes Aminotransferases 1- Aspartate aminotransferase (AST) Also called ( glutamate oxaloacetate aminotransferase, GOT) AST Aspartate + α-ketoglutarate oxaloacetate +glutamate AST is present in high concentrations in : Cardiac muscle Erythrocytes Skeletal muscle liver Kidneys Causes of raised plasma AST activity  Artefactual: due to in vitro release from RBC if there is hemolysis  Marked increase (may be greater than 5–10 times the upper reference limit or URL): – Circulatory failure with ‘shock’ and hypoxia – Myocardial infarction – Acute viral or toxic hepatitis  Moderate to slight increase (usually less than five times URL): -Cirrhosis -Liver tumors -skeletal muscle disease  Liver 2-Alanine aminotransferase(ALT) Skeletal m. ALT α-ketoglutarate + L-alanine L-glutamate + pyruvate It is also called (Glutamate pyruvate aminotransferase GPT ) Kidneys Cardiac m.  Causes of raised plasma ALT activity :  Marked increase (may be greater than 5–10 times URL): – Circulatory failure with ‘shock’ and hypoxia, – Acute viral or toxic hepatitis.  Moderate to slight increase (usually less than five times URL): – Liver cirrhosis – Liver tumors Lactate dehydrogenase (LDH) LDH Lactate + NAD+ pyruvate + NADH + H Skeletal muscle Kidneys Brain Cardiac Liver RBCS muscle  Causes of raised plasma total LDH activity  Artefactual: due to in vitro hemolysis  Marked increase (may be greater than 5–10 times URL): – Circulatory failure with ‘shock’ and hypoxia – Myocardial infarction – Some hematological disorders: in blood diseases such as megaloblastic anaemia, acute leukemia and lymphomas  Moderate to slight increase (usually less than five times URL): – Viral hepatitis – Malignancy of any tissue  Isoenzymes of LDH Five main isoenzymes can be detected by electrophoresis and are referred to as LDH1 to LDH5 The five isoenzymes of LDH consist of 2 different kinds of polypeptide chains designed as H and M. Isoenzyme Composition Tissue Elevated in name distribution LDH1 H4 Heart MI LDH2 H3M1 Heart , kidney, MI , hemolytic anemia RBCS LDH3 H2M2 Widely distributed Malignancy of many tissues LDH4 H1M3 Widely distributed Little significance LDH5 M4 Liver, skeletal Skeletal muscle and liver muscle diseases  Creatine kinase Isoenzymes of creatine kinase There are three principal CK isoenzymes, each comprising two polypeptide chains, either B or M; these give the dimers BB, MB and MM.  Isoenzymes of creatine kinase BB (CK-1) MB (CK-2) MM (CK-3) Predominate Predominate in Predominate in in the brain cardiac muscle skeletal muscle  Other forms of CK Mitochondrial CK Seen in hepatic disease, certain tumors and critically ill patients. Type 1 macroenzyme Associated with autoimmune disease such as rheumatoid arthritis and is thought to be CK complexed with IgG Type 2 macroenzyme It is an oligomer of mitochondrial CK.  Causes of raised plasma creatine kinase activities Marked increase (may be greater than 5–10 times URL): – Dermatomyositis and polymyositis – ‘Shock’ and circulatory failure – Myocardial infarction Moderate to slight increase (usually less than five times URL): – Muscle injury – Physical exertion – After an intramuscular injection – Hypothyroidism – Certain drugs, for example statins, ciclosporin , cocaine Amylase Breaks down starch and glycogen Amylase in serum arises mainly from the pancreas (P- isoamylase) and the salivary glands (S-isoamylase). It may be extracted from other tissues, such as the gonads, Fallopian tubes, skeletal muscle and adipose tissue. It is excreted in the urine, due to its relatively low molecular weight. Causes of raised plasma amylase activity  Marked increase (may be greater than 5–10 times URL): -Acute pancreatitis -Severe glomerular impairment -Diabetic ketoacidosis -Perforated peptic ulcer  Moderate to slight increase (usually less than five times URL) Other acute abdominal disorders: - Acute cholecystitis - Intestinal obstruction Salivary gland disorders: mumps, salivary calculi It is decreased in : Chronic pancreatic disease  Macroamylasaemia In some patients, high plasma amylase activity is due to low renal excretion of a macroenzyme form, despite normal glomerular function. The condition is symptomless and it is thought that the enzyme is bound to IgA, giving a complex of molecular weight about 270kDa.  Lipase It is also derived from the pancreas but is more specific for pancreatic pathology. lipase has a longer half-life than amylase and therefore may be more useful in the diagnosis of late-presenting acute pancreatitis. Thank you