Definition of Gamma-glutamyl transpeptidase:

Gamma-glutamyl transpeptidase (GGT) is a test to measure the amount of the enzyme GGT in the blood.

How the test is performed:

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test:

The health care provider may advise you to stop taking any drugs that can affect the test.

• Drugs that can increase GGT levels include alcohol, phenytoin, and phenobarbital.
• Drugs that can decrease GGT levels include clofibrate and birth control pills.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

This test is used to detect diseases of the liver or bile ducts. It is also done with other tests (such as the ALT, ALP, and bilirubin tests) to tell the difference between liver or bile duct disorders and bone disease.