The gamma-glutamyl transferase (GGT) blood test measures the level of the enzyme GGT in the blood.
How the Test is Performed
A blood sample is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
How to Prepare for the Test
The health care provider may tell you to stop taking medicines that can affect the test.
Drugs that can increase GGT level include:
Drugs that can decrease GGT level include:
- Birth control pills
The normal range for adults is 0 to 30 U/L (0 to 0.5 µkat/L).
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your provider about the meaning of your specific test results.
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Bleeding from where the needle was inserted
- Fainting or feeling lightheaded
- Hematoma (blood collecting under the skin)
- Infection (rare)
What Abnormal Results Mean
An increased GGT level may be due to any of the following:
Why the Test is Performed
GGT is an enzyme found in high level in the liver, kidney, pancreas, heart, and brain. It is also found in lesser amount in other tissues. An enzyme is a protein that causes a specific chemical change in the body.
This test is used to detect diseases of the liver or bile ducts. It is also done with other tests (such as the ALT, AST, ALP, and bilirubin tests) to tell the difference between liver or bile duct disorders and bone disease.
It may also be done to screen for, or monitor, alcohol use.
Chernecky CC, Berger BJ. Gamma-glutamyltranspeptidase (GGTP, gamma-glutamyltransferase) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:559-560.
Pratt DS. Liver chemistry and function tests. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 73.