GammaGT

Gamma-glutamyl transferase (GGT) is an enzyme that catalyzes transfer of gamma-glutamyl functional groups in the gamma-glutamyl cycle, playing a role in glutathione metabolism and the transport of amino acids into cells. It is concentrated in high amounts in the liver, particularly in the bile ducts, and is also present in other tissues such as the kidney, pancreas, and intestine. GGT can be detected in the plasma and is often measured in serum as part of liver function testing.

Clinical use and interpretation

Serum GGT is a sensitive biomarker for hepatobiliary disease, especially conditions affecting bile flow. Elevated GGT levels are commonly seen with cholestasis, alcoholic liver disease, and fatty liver disease, and can also occur with pancreatic disorders or congestive heart failure. However, GGT is not specific to liver disease and can be increased by various medications (such as anticonvulsants and certain lipid-lowering drugs), alcohol consumption, and other factors. Because of its limited specificity, GGT is typically interpreted alongside other laboratory tests, particularly alkaline phosphatase and transaminases (ALT and AST), to help distinguish hepatic from bone sources and to assess the pattern of liver injury.

Measurement and interpretation

GGT is measured from a serum sample using a biochemical assay and reported in units per liter. Reference ranges vary by laboratory and age, and levels may be influenced by age, pregnancy, and concurrent medications. In clinical practice, a normal GGT with elevated alkaline phosphatase points away from hepatobiliary disease, while a simultaneous rise in GGT and ALP supports a liver-related cholestatic process.