Also known as: Gamma-glutamyl transpeptidase, GGTP
Name: Gamma-glutamyl transpeptidase
Related tests: ALP, ALT, AST, Bilirubin, Liver panel
Why is the test done?
To detect liver disease and/or alcohol abuse; when ALP is high, to distinguish between liver and bone disease.
When is it done?
When your doctor suspects liver disease.
What samples are required?
A blood sample from a vein in the arm.
What is being analysed?
GGT is an enzyme found mainly in the liver; it is a very sensitive marker of impaired liver function. Normally it is present in the blood in small amounts. GGT levels rise if the liver is damaged or the bile ducts are blocked. It is the most sensitive liver enzyme for detecting bile duct abnormalities. In some cases, however, GGT may rise in the blood with no identifiable liver cause.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
GGT is useful for detecting functional abnormalities of the liver and bile ducts. While some doctors use it in all patients in whom they suspect liver disease, others request it only after other tests are found to be abnormal or when alcohol abuse is suspected. For example, both ALP and GGT rise in diseases affecting the bile ducts, while in bone diseases ALP rises
on its own. In other words, if a person has high ALP and normal GGT, it is probably due to a disease affecting the bones. GGT is also used to detect chronic alcohol abuse (it is raised in 75% of chronic alcoholics).
When is it requested?
GGT is usually requested together with other tests in patients with signs or symptoms of liver disease, including jaundice, nausea, vomiting, abdominal swelling, abdominal pain, itching and tiredness.
GGT rises in most cases of acute damage to the liver or bile ducts,
but it does not help to show what caused it.
For this reason the use of GGT is debated, and the guidelines published by the National Academy of Clinical Biochemistry and the American Association for the Study of Liver Diseases do not recommend its routine use. These guidelines suggest using GGT to find the cause of a raised ALP. In people with a history of chronic alcoholism who have been treated to detoxify, GGT is a useful marker for monitoring the patient’s adherence to the treatment programme.
What does the test result mean?
Doctors are rarely asked about low or normal GGT values; in these cases liver disease is considered unlikely.
High GGT levels indicate that the liver is involved, but do not suggest what type of problem it is.
In general, the higher the GGT levels, the greater the damage to the liver. High levels can occur with liver disease, but also with congestive heart failure, alcohol abuse and certain prescription or over-the-counter medicines, including non-steroidal anti-inflammatory drugs (NSAIDs), cholesterol-lowering medicines, antibiotics, histamine receptor blockers (antacids used to treat excess stomach acid), antifungals, weight-control medicines, antidepressants and hormones such as testosterone. Oral contraceptives (birth control pills) and clofibrate can lower GGT levels.
Is there anything else I should know?
Even small amounts of alcohol taken in the 24 hours before the blood test can cause temporary rises in GGT. In these cases the doctor may ask for the test to be repeated to check that it has returned to the normal range.
GGT falls after meals, so you should not eat for at least eight hours before the blood test.
Smoking can also raise GGT.
GGT levels rise with age in women but not in men, while at the same age they are higher in men.
In people of African descent, GGT is higher, about twice that of Europeans
1. Can high GGT levels be found without any symptoms?
2. I used to be an alcoholic but I have now stopped drinking. Will my GGT values return to normal?
1. Can high GGT levels be found without any symptoms?
Yes. GGT is a very sensitive marker that rises before symptoms appear. Increases can be temporary, for example due to taking certain medicines or alcohol in the 24 hours before the blood test. If the other liver enzymes are normal, the doctor will probably wait a few days and ask for the test to be repeated. If, however, GGT levels are very high and/or other liver enzymes are raised, the doctor will probably request further tests to find the cause.
2. I used to be an alcoholic but I have now stopped drinking. Will my GGT values return to normal?
Yes. Over time, whatever level they reached, GGT values will return to roughly normal once you stop drinking. It takes at least a month after stopping drinking for GGT levels to return to normal. Abstaining from alcohol will allow you to reduce the damage alcohol has done to your liver and improve its function.