Gamma Glutamyl Transpeptidase (GGT)
A biliary enzyme that is especially useful in the diagnosis of obstructive jaundice, intrahepatic cholestasis, and pancreatitis.1 GT is more responsive to biliary obstruction than are aspartate aminotransferase (AST) (SGOT) and alanine aminotransferase (ALT) (SGPT).
Increased in hepatoma and carcinoma of pancreas. Useful in diagnosis of metastatic carcinoma in the liver. Increasing levels in carcinoma patients relate to tumor progression, and diminishing levels to response to treatment.2 CEA, alkaline phosphatase, and GT used together are useful markers for hepatic metastasis from breast and colon primaries. GT is elevated in some instances of seminoma.
Useful in diagnosis of chronic alcoholic liver disease, but some heavy drinkers do not have GT increases. Serial determinations of serum GT, AST, and ALT levels can distinguish recovering alcoholics who resume drinking from those who remain abstinent.3,4 Increase in body mass is positively correlated with increased GT levels.5 With MCV of red cells, GT is useful as a test for alcoholism.GT is the test for cholestasis during or immediately following pregnancy. Commonly elevated in cirrhosis and hepatitis. The transaminases, AST and ALT rise higher in acute viral hepatitis; these tests with GT and other parameters are best used together in work-up of liver disease.Increased in systemic lupus erythematosus.2 Very high levels are common in primary biliary cirrhosis. High GT is found in infants with biliary atresia. It is increased with hyperthyroidism and decreased in those with hypothyroidism.6 GT is comparable in many ways to two other biliary tests, LAP and 5′ nucleotidase. In some cases, five tests (including alkaline phosphatase and bilirubin) are necessary to evaluate the biliary tract. GT usually is the most sensitive.In ascitic fluid, very high GT is said to suggest hepatoma as opposed to cirrhosis or liver metastases.
Serum (preferred) or plasma
Red-top tube, gel-barrier tube, green-top (heparin) tube, or lavender-top (EDTA) tube
The patient should fast for eight hours prior to collection of the specimen. Since there are false elevations in patients on phenytoin and phenobarbital, such patients would be better served with orders for one of the alternate tests − leucine aminopeptidase (LAP) or 5′ nucleotidase.
Separate serum or plasma from cells within 45 minutes of collection
Maintain specimen at room temperature.
Gross hemolysis; improper labeling; gross lipemia
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