Gamma-glutamyl Transferase (GGT) Test

Why this test may be ordered

• To help diagnose liver disease.
• To determine if liver damage is due to liver disease or a bone disorder.
• To check for blockages in the bile ducts.
• To screen for or monitor alcohol use disorder (AUD).

Preparation and collection

Talk to your provider about specific instructions. Some medicines, supplements, alcohol, or smoking may affect results. GGT levels drop after meals, so your provider may ask you to fast for a certain amount of time before testing.

A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Understanding results

Your GGT test measures the amount of this enzyme in your blood. High levels may indicate liver damage, but the test cannot determine the specific cause. Low or normal levels mean you probably don't have liver disease.

• High GGT: Higher-than-normal GGT levels may indicate liver damage or bile duct problems. Limitation: Cannot diagnose the specific cause of liver disease; only indicates damage. Results may be affected by medicines, alcohol, smoking, or recent meals. Next step: Your provider will evaluate your symptoms, medical history, and other tests (e.g., ALP, ALT, AST) to identify the cause. If your ALP is also high, it suggests a liver disorder rather than a bone disorder.
• Low or Normal GGT: Low or normal GGT levels mean you probably don't have liver disease. Limitation: Does not rule out all liver conditions, but makes significant liver disease unlikely. Results may be affected by factors like recent meals. Next step: If your ALP is high, your provider will likely investigate a bone disorder. If ALP is normal, no further liver workup may be needed based on this test alone.

• Cannot diagnose the specific cause of liver disease; only indicates liver damage.
• Results may be affected by certain medicines, supplements, alcohol, smoking, or recent meals.
• Provides no information about bone disorders without comparison with an ALP test.

What to do next

Your healthcare provider will interpret your GGT results along with your symptoms, medical history, and other liver function tests (e.g., ALP, ALT, AST, LDH) to understand your condition.

• What do my GGT results mean in combination with my ALP and other liver tests?
• Do I have any signs of liver damage that need further investigation?
• Should I avoid any medications or alcohol before a repeat test?
• How often should I have this test if I am being monitored for alcohol use disorder?

Evidence source

U.S. National Library of Medicine: Gamma-glutamyl Transferase (GGT) Test