GGT

Gamma-glutamyl transferase (GGT), also known as gamma-glutamyl transpeptidase, is a membrane-bound enzyme that participates in the gamma-glutamyl cycle and glutathione metabolism. It is expressed on the surface of many cell types, with particularly high activity in the liver, bile duct epithelium, kidney, and pancreas.

GGT catalyzes the transfer of the gamma-glutamyl group from glutathione to an amino acid or peptide, a reaction that helps in glutathione homeostasis and the transport of amino acids into cells. Through its role in glutathione metabolism, GGT contributes to cellular detoxification processes and antioxidant defense.

In clinical practice, serum GGT is used as a biomarker of hepatobiliary disease and alcohol exposure. Levels rise in cholestasis and biliary obstruction, as well as in various liver conditions including alcoholic liver disease, non-alcoholic fatty liver disease, hepatitis, and cirrhosis. GGT can also be elevated in pancreatic disease and certain drug-induced liver injury. However, it is relatively non-specific and may be increased in non-hepatic states such as heart failure or metabolic disorders. Therefore GGT is often interpreted together with alkaline phosphatase (ALP) and other clinical information.

Measurement is typically performed on serum using enzymatic assays. Reference ranges vary by laboratory but commonly fall roughly in the 9 to 48 U/L range for adults, with adjustments for age, sex, and methodological differences. No special fasting is usually required, though individual lab requirements may apply.