Gamma-Glutamyl Transferase (GGT)

What is Gamma-Glutamyl Transferase (GGT)?

An enzyme concentrated in the liver and bile ducts; GGT is often used to confirm that a raised alkaline phosphatase is coming from the liver rather than bone.

Gamma-glutamyl transferase (GGT) is an enzyme found throughout the body but concentrated in the liver and bile ducts, and its main clinical use is to help interpret an elevated alkaline phosphatase. When both GGT and ALP are raised, the picture points toward a liver or biliary source; when ALP is high but GGT is normal, a bone origin becomes more likely. GGT is sensitive but not specific, meaning many influences can raise it, including alcohol intake and certain medicines, so it cannot by itself name a cause. It is often ordered with or after other liver function tests when bile-flow problems or alcohol-related liver effects are being considered. Because GGT can respond to many factors, clinicians read it as a supporting clue rather than a standalone diagnosis.

Tests often checked alongside this

• ALP (alkaline phosphatase) — GGT is used to confirm whether a raised ALP is liver or bone in origin
• ALT and AST — describe accompanying liver-cell injury
• Total bilirubin — helps characterize a bile-flow (cholestatic) pattern
• Direct bilirubin — supports assessment of impaired bile excretion

How this can show up in how you look and feel

• GGT is a blood measurement and does not cause symptoms on its own
• A high GGT can be associated with liver or bile-duct conditions sometimes seen with fatigue or jaundice
• Elevated GGT is sometimes seen with heavier alcohol use, though on its own it does not diagnose this
• Many people with a raised GGT have no noticeable symptoms

What can affect this marker

• Alcohol intake
• Certain prescription and over-the-counter medicines
• Liver or bile-duct conditions
• Body weight and liver fat, and in some cases smoking

What to track over time

• Your GGT trend over repeated tests
• Whether GGT moves together with ALP
• Alcohol intake and new medications before testing
• Related liver markers such as ALT, AST, and bilirubin

What to ask your doctor

• Does my GGT confirm a liver or biliary source for my other results?
• Could alcohol or a medication be influencing my GGT?
• Should GGT be rechecked after any lifestyle changes?
• What further tests, if any, does my overall pattern suggest?

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