The gamma-glutamyl transferase (GGT) test measures the level of GGT enzyme found in the liver and bile ducts, in the blood. This test is commonly used to evaluate liver function and detect liver disease, bile duct obstruction, or alcohol abuse. Elevated GGT levels may indicate liver damage, cholestasis, or certain types of liver disease, and it can also be used to monitor the effectiveness of treatment for liver disorders. A blood sample is analyzed to assess GGT levels, providing valuable information about hepatic health.