Gamma-Glutamyl Transferase (GGT)

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.

• Men: about 10-70 U/L.
• Women: about 6-42 U/L - typically a little lower.
• Sensitive to alcohol and fatty liver, so mild elevations are common and often reversible.
• Read together with ALT, AST and ALP to place a liver picture.

Your lab's printed range is what counts.

• 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.

• Usually not clinically actionable.
• Vitamin B6 deficiency — same cofactor dependency as ALT/AST.

• GGT usually causes no symptoms on its own - a mild rise is often found incidentally.
• When it reflects significant liver strain, non-specific signs like fatigue or abdominal discomfort can appear; jaundice suggests more advanced disease.
• Its main value is as a sensitive early flag, read alongside the other liver tests.