The Gamma-Glutamyl Transferase (GGT) test is a common blood test that measures the amount of the enzyme GGT in your bloodstream. GGT is found in many tissues, but it is especially concentrated in the liver and the system that carries bile (the bile ducts). Because of this, the GGT test is often used as part of a liver function evaluation and to help identify problems affecting the liver or bile duct system.

What GGT levels can mean: When liver cells are irritated or damaged, or when bile flow is blocked, more GGT can leak into the blood, causing elevated enzyme levels. A high GGT result does not point to one single diagnosis on its own, but it can be an important clue that guides further testing. Mild to moderate increases may be seen with many liver-related conditions or certain medications, while higher elevations can occur with more significant liver or bile duct problems.

GGT is frequently interpreted alongside other liver enzymes—such as alkaline phosphatase (ALP), ALT, and AST. For example, if ALP is high and GGT is also high, this pattern often suggests a liver or bile duct source for the abnormality (rather than a bone-related cause of high ALP). If GGT is normal while ALP is elevated, your clinician may consider non-liver causes and may order additional tests.

Your clinician may order a GGT test when there are signs, symptoms, or other test results that suggest a possible liver or bile duct issue, or to help clarify abnormal findings on a routine panel. It may also be used to monitor known liver disease or assess whether something (such as alcohol use or a medication) could be affecting the liver.

Common reasons a GGT test is ordered include:

Symptoms that may suggest liver disease or bile duct obstruction such as:

• Yellowing of the skin or eyes (jaundice)

• Dark urine or pale/clay-colored stools

• Itching (sometimes linked to bile flow problems)

• Pain or fullness in the upper right abdomen

• Nausea, vomiting, poor appetite, or unexplained weight loss

• Unusual fatigue or weakness

Abnormal blood work such as:

• Elevated alkaline phosphatase (ALP) (GGT helps determine if the ALP elevation is likely from the liver/bile ducts)

• Abnormal ALT/AST or bilirubin on a liver panel

Risk factors or clinical situations where liver testing is commonly needed:

• Regular or heavy alcohol use, or concern for alcohol-related liver injury

• Use of medications that can affect the liver (your clinician will interpret results in context)

• Viral hepatitis exposure risks or known hepatitis

• Metabolic risk factors associated with fatty liver (e.g., obesity, insulin resistance, type 2 diabetes, high triglycerides)

• Follow-up and monitoring of known liver disease or suspected bile duct problems

Because many conditions can raise GGT, your healthcare provider typically evaluates the result together with your symptoms, medical history, alcohol intake, medications/supplements, and other labs and imaging to reach the most accurate diagnosis.

• Alcohol-related liver disease

• Nonalcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH)

• Viral hepatitis (e.g., hepatitis B or C)

• Cirrhosis

• Bile duct obstruction (cholestasis), including gallstones blocking the bile duct

• Cholangitis (infection/inflammation of the bile ducts)

• Primary biliary cholangitis (PBC)

• Primary sclerosing cholangitis (PSC)

• Drug-induced liver injury (medication- or supplement-related)

• Liver tumors or metastatic cancer affecting the liver/bile ducts

• Pancreatic disease that compresses or obstructs the bile duct (in some cases)

• Monitoring liver function as part of routine wellness screening or follow-up care

• Clarifying elevated alkaline phosphatase results to determine if the source is likely liver/bile duct related

• Tracking and managing liver disease over time (e.g., hepatitis, fatty liver, cirrhosis)

• Assessing possible bile duct blockage or impaired bile flow when symptoms suggest cholestasis

• Evaluating potential liver effects of alcohol use as part of risk reduction and treatment planning

• Supporting medication safety monitoring when taking drugs that may affect the liver (as directed by a clinician)

• Guiding next-step diagnostic testing (additional blood tests and/or imaging) when liver enzyme levels are abnormal