Gamma-glutamyl transferase (GGT) is an enzyme found primarily in the liver and biliary system that plays a role in amino acid transport and glutathione metabolism. This test measures GGT levels in the blood and is particularly useful for evaluating liver and bile duct function. GGT is highly sensitive to biliary obstruction and is often elevated in conditions affecting the bile ducts, such as gallstones, tumors, or inflammation. Elevated GGT levels can also indicate liver damage from alcohol, medications, or various liver diseases including hepatitis, cirrhosis, and fatty liver disease. GGT is often used in combination with other liver function tests to provide a comprehensive picture of liver health. This test is commonly ordered when evaluating patients with suspected liver disease, unexplained liver enzyme elevations, or when monitoring the progression of known liver conditions.