Gamma-glutamyl transferase (GGT) is an enzyme found in many tissues of the body, with the highest concentrations in the liver. This blood test measures the amount of GGT in your blood. Levels can rise when the liver or bile ducts are affected, and GGT is often measured alongside other liver enzymes to help evaluate liver health. The test is used to help detect and evaluate liver or bile duct conditions. It is often ordered when other liver tests are abnormal, to help determine whether an elevated alkaline phosphatase level is coming from the liver or from bone. GGT is also sometimes used to help assess conditions related to alcohol use.