Gamma‑glutamyl transferase (GGT) is a membrane enzyme that recycles glutathione, the body’s primary antioxidant, and is concentrated in the liver and bile ducts. Because it sits at the crossroads of bile flow, detoxification, and oxidative stress handling, GGT is a sensitive readout of hepatobiliary strain and whole‑body redox burden. Most adult reference ranges span the low to mid double digits; health risk tends to be lowest when values sit in the lower half of normal. Men often run slightly higher than women; newborns are transiently higher, then values settle in childhood.When GGT is low or low‑normal, it generally reflects minimal enzyme induction and a lighter oxidative stress load. People usually feel well and have no symptoms. Pregnancy often shows lower GGT, and many children have low‑normal values for age. Exceptionally rare inherited disorders of this enzyme present in infancy and are diagnosed clinically.When GGT is elevated, it signals either impaired bile flow or increased enzyme induction in the liver. Common drivers include alcohol exposure, certain medications, fatty liver related to weight or insulin resistance, viral or autoimmune hepatitis, and bile duct obstruction. Symptoms, when present, can include fatigue, itching, right‑upper‑abdominal discomfort, dark urine, pale stools, and jaundice. A high GGT alongside a high alkaline phosphatase supports a liver/bile‑duct source. Even high‑normal GGT tracks with metabolic syndrome, type 2 diabetes, and cardiovascular risk; in pregnancy, a rise is less typical and may suggest non‑pregnancy‑specific liver disease.Big picture: GGT links liver function with antioxidant recycling and metabolic health. Interpreted with ALT, AST, alkaline phosphatase, bilirubin, and imaging, it helps gauge fatty liver burden, cholestasis, and long‑term risks such as fibrosis, diabetes, and heart disease.
