Gamma-Glutamyl Transferase (GGT)
GGT is a bile-duct enzyme — its rise alongside alkaline phosphatase confirms the elevated ALP comes from the liver, not bone.
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What it measures
GGT lives on the membranes of biliary epithelial cells. When bile flow is obstructed or bile-duct cells are stressed, GGT leaks into the bloodstream. The diagnostic usefulness of GGT is mostly comparative: alkaline phosphatase (ALP) can rise from bone, placenta or liver, and GGT is the tiebreaker — high ALP + high GGT = liver/biliary origin; high ALP + normal GGT = bone or placenta. GGT is also one of the most sensitive markers of alcohol-related liver injury.
What a high value can mean
- Cholestasis — bile-duct obstruction, primary biliary cholangitis, primary sclerosing cholangitis.
- Alcohol — chronic heavy use raises GGT, often before ALT/AST.
- Drug-induced liver injury — phenytoin, barbiturates, NSAIDs, statins (rarely).
- NAFLD — frequently elevated alongside ALT.
- Smoking, obesity — modestly raise GGT.
What a low value can mean
- Usually not clinically actionable.
- Vitamin B6 deficiency — same cofactor dependency as ALT/AST.
When to discuss with a doctor
An isolated GGT elevation (with normal ALP, ALT, AST) is often dismissable — alcohol, obesity or medication. Persistent elevation alongside ALP indicates a true biliary issue worth a primary-care visit, ultrasound and possibly MRCP. Mediora.AI shows GGT in context with the rest of the liver panel.