Gamma-glutamyl transferase (GGT)

What it measures

GGT sits on the surface of cells in the liver, bile ducts, kidneys, and pancreas. Blockage or irritation of the bile ducts raises it sharply. Regular alcohol use, fatty liver, obesity, diabetes, and smoking raise it more modestly. Some medicines, including certain seizure drugs such as phenytoin and carbamazepine, raise GGT without liver damage. Bone disease does not raise GGT, which makes it useful next to ALP.

Who should consider it

• People with a high ALP on a CMP or liver panel
• People who want to track how alcohol affects their liver tests
• Adults with fatty liver risk who want a fuller liver picture
• People on long-term medicines that affect liver enzymes

How to read your result

• Reference ranges differ by lab and often run higher in men. Use the range printed on your report.
• A high GGT with a high ALP points to the liver or bile ducts. A normal GGT with a high ALP points more toward bone.
• A high GGT alone does not prove alcohol use or liver disease. Medicines, weight, and fatty liver commonly raise it.
• After someone stops drinking heavily, GGT usually takes several weeks to fall, so a single result reflects recent weeks of habits.

Reference ranges differ between labs. Use the range printed on your own report.

What to do next

Read GGT together with ALT, AST, ALP, and bilirubin. If it stays high, a clinician can review alcohol use, medicines, and fatty liver risk, and may order an ultrasound or more liver tests.