gammaglutamyltransferase

Gammaglutamyltransferase (GGT) is a membrane-bound enzyme that participates in the gamma-glutamyl cycle, transferring gamma-glutamyl groups from glutathione to amino acids or peptides. It is widely distributed in tissues with the highest activity in the liver, particularly in the biliary epithelium, and is also found in kidney, pancreas, and intestine. Serum GGT activity is commonly measured as part of liver function tests to help detect biliary tract disorders and to characterize liver injury.

Clinical significance: GGT is a sensitive marker of hepatobiliary disease and cholestasis but is not specific for a single condition. Elevations occur with alcoholic liver disease, nonalcoholic fatty liver disease, viral hepatitis, cirrhosis, biliary obstruction, and drug-induced cholestasis. GGT can also be increased with excessive alcohol use and by certain medications such as anticonvulsants and rifampin. Because GGT can be influenced by multiple factors and is not organ-specific, its interpretation should be made in conjunction with other liver tests (ALT, AST, alkaline phosphatase) and clinical context.

Measurement and interpretation: Normal values vary by laboratory, age, sex, and assay. GGT is most informative when considered alongside a pattern of liver enzyme abnormalities rather than in isolation. A persistently elevated GGT may prompt further evaluation for biliary obstruction, alcoholic liver disease, fatty liver disease, or drug effects, often including imaging and additional laboratory assessments.