What is a gamma-glutamyl transferase (GGT) test?
A gamma-glutamyl transferase (GGT) test measures the amount of GGT in the blood. GGT is an enzyme found throughout the body, but it is mostly found in the liver. When the liver is damaged, GGT may leak into the bloodstream. High levels of GGT in the blood may be a sign of liver disease or damage to the bile ducts. Bile ducts are tubes that carry bile in and out of the liver. Bile is a fluid made by the liver. It is important for digestion.
A GGT test can’t diagnose the specific cause of liver disease. So it is usually done along with or after other liver function tests, most often an alkaline phosphatase (ALP) test. ALP is another type of liver enzyme. It’s often used to help diagnose bone disorders as well as liver disease.
Other names: gamma-glutamyl transpeptidase, GGTP, Gamma-GT, GTP
What is it used for?
A GGT test is most often used to:
- Help diagnose liver disease
- Figure out if liver damage is due to liver disease or a bone disorder
- Check for blockages in the bile ducts
- Screen for or monitor alcohol use disorder
Why do I need a GGT test?
You may need a GGT test if you have symptoms of liver disease. Symptoms include:
- Jaundice, a condition that causes your skin and eyes to turn yellow
- Loss of appetite
- Abdominal pain or swelling
- Nausea and vomiting
You may also need this test if you had abnormal results on an ALP test and/or other liver function tests.
What happens during a GGT test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don’t need any special preparations for a GGT test.
Are there any risks to a GGT test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
If your results show higher than normal levels of GGT, it may be a sign of liver damage. The damage may be due to one of the following conditions:
- Alcohol use disorder
- Congestive heart failure
- Side effect of a drug. Certain medicines can cause liver damage in some people.
The results can’t show which condition you have, but it can help show how much liver damage you have. Usually, the higher the level of GGT, the greater the level of damage to the liver.
If your results show you have low or normal levels of GGT, it means you probably don’t have liver disease.
Your results may also be compared with the results of an ALP test. ALP tests help diagnose bone disorders. Together your results may show one of the following:
- High levels of ALP and high levels of GGT means your symptoms are likely due to liver disorder and not a bone disorder.
- High levels of ALP and low or normal GGT means it’s more likely you have a bone disorder.
If you have questions about your results, talk to your health care provider.
Is there anything else I need to know about a GGT test?
In addition to an ALP test, your provider may order liver function tests along with or after the GGT test. These include:
- Alanine aminotransferase, or ALT
- Aspartate aminotransferase, or AST
- Lactic dehydrogenase, or LDH