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Gamma-Glutamyl Transpeptidase

Does this test have other names?

GGTP, gamma-glutamyl transferase, GGT

What is this test?

This test looks for an enzyme, or protein, called gamma-glutamyl transpeptidase (GGT) in your blood.

GGT is found in liver cells. This test helps your doctor look for possible damage to your liver or its ducts. It can also help tell the difference between liver and bone disease if your results from a different blood test called alkaline phosphatase are abnormal.

Why do I need this test?

You may need this test if your doctor suspects that you have liver damage. One symptom of liver damage is jaundice, a yellowish tint to your skin and eyes. You may also need this test to see if you have liver or bone disease. This test is also used to look for chronic alcohol abuse.

What other tests might I have along with this test?

Your doctor may also order other liver enzyme tests, including:

  • Alanine aminotransferase, or ALT

  • Alkaline phosphatase, or ALP

  • Aspartate aminotransferase, or AST 

  • 5'-Nucleotidase

  • Creatine phosphokinase, or CPK

  • Lactic dehydrogenase, or LDH

  • Leucine aminopeptidase, or LAP 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in international units per liter (U/L). Normal findings are:

  • 8 to 38 U/L for women older than 45 and all men

  • 5 to 27 U/L for women younger than 45

Older adults may have slightly higher levels. Normal results for children are much like those for adults. A newborn's level is five times higher than an adult's.

Higher than normal test results could be a sign of liver damage from diseases such as hepatitis, cirrhosis, tumors, or pancreatic cancer. But a higher than normal GGT level does not tell you the specific cause of liver disease or damage.

GGT is often higher a week or two after you've had a heart attack, but it's unclear why this happens.

Higher GGT levels also may mean liver damage from heavy, chronic alcohol abuse. GGT levels that are higher than normal may also signal a viral infection, such as Epstein-Barr.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Your test results might be affected if you are near the end of your pregnancy. Phenobarbital and phenytoin can increase your GGT levels. Other medications, such as clofibrate and oral contraceptives, can lower your levels.

How do I get ready for this test?

You must not eat or drink anything but water for eight hours before having this test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.