Enzymes of diagnostic value

ENZYMES OF DIAGNOSTIC VALUE

Transaminases

  • These are enzymes involved in the trasfer of amino from an amino acid to a keto acid.
  • Two aminotransferases are in use in diagnostic enzymology. They are
    • Aspartate Amino Transaminase (AST) and
    • Alanine Amino Transaminase (ALT).
  • Aspartate Transaminase: (Also known as Serum Glutamate Oxaloacetate Transaminase)(SGOT/GOT)
    • Both the enzymes are widely distributed in the body tissues such as heart, liver, skeletal muscle, kidney and erythrocytes.
    • Damage to any of these tissues may increase plasma AST level.
    • Causes of rise in plasma AST
      • In vitro hemolysis.
      • Circulatory failure with shock and hypoxia· 
      • Myocardial infarction·
      • Acute viral or toxic hepatitis·
      • Cirrhosis·
      • Cholestatic jaundice·
      • Skeletal muscle disease·
      • Severe hemolytic anemia·
      •  After surgery.
    • ALT is increased in hepatocellular injury in dog and cat. It is not useful in evaluating chronic liver disease.
    • ALT may also be elevated in corticosteriod treatment. This enzyme is not useful in evaluating hepatic disease in horse, cow, sheep, goat and pig.
    • Elevation of AST is more specific than that of ALT in evaluating hepatic disorders in large animals.
  • Alanine Transaminase  Also know as Alanine transaminase (ALT) or  Serum Glutamate Pyruvate Transaminase
  • (SGPT/GPT)
    • In most conditions where AST is elevated there is a concurrent smaller raise in ALT.
    • In hepatitis plasma levels of ALT may exceed those of AST. 

Alkaline Phosphatase

  • Alkaline Phosphatase are group of enzymes which hydrolyze phosphates at high pH.
  • This enzyme is present in high concentrations in liver, bone (osteoblast) placenta and intestinal epithelium.
  • Each of these tissues contain specific isoenzymes of ALP.
  • In general serum alkaline phosphatase activity is increased in bone and liver diseases.
    • Bone Diseases
      • Osteomalacia and Rickets.
      • Paget’s disease of bone.
      • Carcinoma in bone.
    • Liver Diseases
      • Intra and extra hepatic cholestasis.
      • In lesions and tumour.

Acid Phosphatase (ACP)

  • This enzyme is present in high concentrations in the prostate gland, liver, rbc, platelets and bone.
  • And it is elevated in the plasma of some patients with prostatic cancer.

Lactate Dehydrogenase (LDH)

  • This enzyme catalises the reversible interconversion of lactate and pyruvate.
  • This enzyme is present in all cells of the body.
  • Serum LDH is increased in liver, heart, skeletal muscle and kidney diseases and also in hepatopoietic and neoplastic disease.
  • A better evaluation of the cause of an elevation of LDH can be ascertained by evaluating the isoenzymes separately.
  • All LDH isoenzymes are found in varying concentrations in all the tissues.
    • There are five well defined LDH isoenzymes.
    • This enzyme exists in the body as a Tetramer.
    • Two  monomers H and M can combine in various proportions.
    • Predominant elevation of LD1 and LD2 occurs after myocardial infarction.
    • Predominant elevation of LD2 and LD3 occurs in acute leukemia.
    • Elevation of LD5 occurs after damage to the liver or skeletal muscle.
    • The means of identification of these isoenzymes is usually by serum electrophoresis.

Creatine Kinase

  • Creatine kinase consists of two protein sub units (dimer) M and B, which combine to form three isoenzymes(BB, MM and MB).
  • BB is confined to the brain.
  • Most of the CK normally present in the plasma is the MM, which comes from skeletal muscle.
  • An increase is seen with the skeletal muscle damage. Cardiac muscle contains MB type isoenzyme.
  • A raised CK-MB is a characteristic of myocardial infarction.

Gama Glutamyl Transferase (GGT)

  • This enzyme is present in high concentration in the liver, kidney and pancreas.
  • Very high plasma activity is due to:
    • Alcoholic hepatitis.
    • Induction by anticonvulsant drugs.
    • Cholestative liver dissorders.
  • GGT is sensitive than ALP for the deduction of cholestatic disease in horse, cattle, sheep and pig.
  • GGT appears in serum as a result of increased synthesisi rather than as a result of leakage from the cells.
  • In acute hepatic injury ALT  and AST are generally elevated and ALP may be normal.
  • In chronic disease with cholestasis, ALP and GGT are elevated and ALT AST may be normal or slightly increased.

Amylase

  • Amylase breaks down starch and glycogen to maltose.
  • It is present at high concentrations in pancreatic juice and in saliva.
  • The plasma activity of this enzyme is very high in acute pancreatitis.

Lipase

  • It is found in the pancreas.
  • Increased amounts of this enzyme indicates disease and inflammation of the pancreas.
  • Lipase is not present in saliva so this test is more useful in the identification of pancreatic disorders. 
Last modified: Monday, 4 June 2012, 7:22 AM