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

Gamma-GT; GGTP; GGT

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

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.

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.

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.

The normal range is 0 to 51 international units per liter (IU/L).

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

Greater-than-normal levels of GGT may indicate:

• Alcohol abuse
• Flow from the liver is blocked (cholestasis)
• Heart failure
• Hepatitis
• Liver ischemia (lack of blood flow)
• Liver necrosis
• Liver tumor
• Scarring of the liver (cirrhosis)
• Use of drugs that are toxic to the liver

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient 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 light-headed
• Hematoma (blood collecting under the skin)
• Infection (rare)

Berk PD, Korenblat KM. Approach to the patient with jaundice or abnormal liver test results. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 150.

Pratt DS. Liver chemistry and function tests. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier;2010:chap 73.