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.
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.