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Gamma-glutamyl transpeptidase

Definition

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

Alternative Names

Gamma-GT; GGTP; GGT

How the test is performed

A blood sample is taken from a vein. This is called a venipuncture.

How to prepare for the test

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

Drugs that can increase GGT levels include:

  • Alcohol
  • Phenytoin
  • Phenobarbital

Drugs that can decrease GGT levels include:

  • Birth control pills
  • Clofibrate 

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.

It may also be done to screen for or monitor alcohol abuse.

Normal Values

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.

What abnormal results mean

Greater-than-normal levels of GGT may be due to:

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

What the risks are

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)

References

Berk P, Korenblat K. Approach to the patient with jaundice or abnormal liver tests. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 149.

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.

Review Date: 1/21/2013
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.
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