γ-Glutamyl Transferase (GGT)

Gamma‑glutamyl transferase (GGT), also known as gamma‑glutamyl transpeptidase or Gamma GT, is used to assess hepatobiliary disease, especially obstructive jaundice and intrahepatic cholestasis, where GGT often responds more than AST or ALT. When alkaline phosphatase is increased, concurrent GGT helps determine whether the source is hepatic versus bone. The assay supports evaluation of primary biliary cholangitis, primary sclerosing cholangitis, pancreatitis, and malignancy affecting the liver or pancreas. GGT is used to monitor alcohol‑related liver disease and to follow patients over time to distinguish abstinence from relapse. Markedly increased activities may occur in biliary atresia and in primary biliary cholangitis. GGT may be increased with hyperthyroidism and decreased with hypothyroidism.

Bile produced by hepatocytes flows through canaliculi into the biliary tree and onward to the intestine. Gamma‑glutamyl transferase, a membrane enzyme of hepatocytes and the biliary epithelium, appears in serum when cholestatic injury disrupts these structures and increases canalicular enzyme release. GGT is highly sensitive for cholestasis and can precede alkaline phosphatase increases, but it lacks specificity because activities rise in a wide range of hepatic and pancreatic disorders and the enzyme is also present in kidney, spleen, pancreas, brain, and prostate. A pattern of elevated alkaline phosphatase with normal GGT does not reliably exclude liver disease, and GGT has limited utility as a stand‑alone tumor marker in malignancy evaluations.