Gamma-glutamyl transferase (GGT) is an enzyme that's mainly found in your liver. Healthcare providers use GGT blood tests to help diagnose liver conditions or to rule out certain medical conditions based on abnormal results from other liver enzyme tests.
Gamma-glutamyl transferase (GGT), also known as gamma-glutamyl transpeptidase, is an enzyme that’s found throughout your body, though it mainly exists in your liver. An enzyme is a type of protein in a cell that acts as a catalyst and allows certain bodily processes to happen. There are thousands of enzymes throughout your body that have important functions.
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A gamma-glutamyl transferase (GGT) blood test measures the activity of GGT in your blood. GGT may leak into your bloodstream if your liver or bile duct is damaged, so having high levels of GGT in your blood may indicate liver disease or damage to your liver’s bile ducts. Bile ducts are tubes that carry bile (a fluid that’s important for digestion) in and out of your liver.
GGT is typically the first liver enzyme to increase in your blood when any of your liver bile ducts become blocked or constricted. Because of this, it’s the most sensitive liver enzyme test for finding bile duct issues.
Since many types of liver issues can cause elevated levels of GGT in your blood, healthcare providers don’t use the test alone to diagnose conditions. Because of this, providers usually order GGT blood test alongside other liver function tests. It’s most often tested alongside an alkaline phosphatase (ALP) blood test, which measures another type of enzyme that’s found in your liver and bones.
Other names for a gamma-glutamyl transferase (GGT) blood test include:
Healthcare providers most often use GGT blood tests to help diagnose liver disease and/or liver bile duct issues. Your provider may have you get a GGT blood test for several reasons, including:
If you’ve had an alkaline phosphatase (ALP) blood test and your results revealed elevated levels, your healthcare provider may use a GGT blood test to determine the cause of the elevated levels. Both ALP and GGT levels become elevated when you have issues with your bile ducts or have certain liver diseases, but only ALP will be elevated if you have bone disease. Because of this, if you have normal GGT levels but a high ALP, the cause of the elevated ALP is most likely a bone condition, not a liver condition.
Your healthcare provider may use a GGT test for diagnostic purposes when you’re experiencing signs and symptoms of possible liver problems. While providers can’t diagnose a condition based solely on GGT levels, it can be an important part of the diagnostic process. Providers often order a GGT blood test alongside other tests, such as the ALT, AST, ALP and bilirubin tests, to help distinguish the difference between liver or bile duct disorders and bone disease.
Signs and symptoms of liver disease include:
Approximately 75% of people who have alcohol use disorder have elevated levels of GGT in their blood, so healthcare providers can use the test to screen for this condition.
If you’re receiving treatment for alcohol use disorder or alcoholic hepatitis, your provider can use a GGT blood test to monitor for alcohol use.
A healthcare provider called a phlebotomist usually performs blood draws, including those for a GGT blood test, but any healthcare provider who is trained in drawing blood can perform this task. The provider then sends the sample to the lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.
Many different types of medications and supplements can affect your GGT levels, so it’s important to tell your healthcare provider about any drugs or dietary supplements you’re taking before you get the test. In some cases, your provider may have you stop taking a medication before the test. Only stop taking medication if your provider tells you to do so.
Even small amounts of alcohol can increase your GGT levels, so your provider may recommend that you not consume any alcohol for at least 24 hours before the test.
You can expect to experience the following during a blood test, or blood draw, which includes a GGT test:
The entire procedure usually takes less than five minutes.
After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.
Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.
In most cases, you should have your test results within one to two business days, though it could take longer.
Blood test reports, including gamma-glutamyl transferase (GGT) test reports, usually provide the following information:
The normal range for gamma-glutamyl transferase (GGT) varies from laboratory to laboratory. One common reference range for adults is 5 to 40 U/L (units per liter). Since ranges can vary depending on the laboratory, it’s important to check your test result report to see what your specific lab’s reference range is.
It’s important to note that GGT levels are, on average, somewhat higher in men and people assigned male at birth than women and people assigned female at birth. In addition, levels of GGT increase with age in women and people assigned female at birth, but not in men and people assigned male at birth.
If you have a low or normal GGT test result, it’s unlikely that you have liver disease or have consumed any alcohol.
Having a higher-than-normal GGT level in your blood may indicate that a condition or disease is damaging your liver. However, the GGT test alone cannot identify the specific cause of the damage. In general, the higher the GGT level, the greater the damage to your liver.
Liver conditions that can cause elevated GGT levels include:
Other conditions that can cause elevated GGT levels include:
It’s important to know that having a high GGT test result does not necessarily mean you have a medical condition. Other factors can affect your GGT levels. Your healthcare provider will take into consideration several factors, including other blood test results and your medical history, when analyzing your results.
If your GGT test result is high, it doesn't necessarily mean that you have a medical condition that needs treatment. Other factors can affect your levels, including:
In addition to the above factors, your healthcare provider will consider many aspects of your health and situation when analyzing your GGT result, including:
If you’re experiencing symptoms of liver damage, such as jaundice or belly pain, call your healthcare provider.
If you’ve been diagnosed with a liver condition and are experiencing concerning symptoms, contact your provider.
If you think you might have a problem with alcohol, talk to your healthcare provider or call the Substance Abuse and Mental Health Services Administration (SAMHSA) hotline at 1-800-662-HELP (4357). They can help you cope, make a treatment plan and refer you to support programs.
A note from Cleveland Clinic
Seeing an abnormal test result can be stressful. Know that having a high level of gamma-glutamyl transferase (GGT) doesn’t necessarily mean you have a medical condition and need treatment. Approximately one in 20 healthy people will have an abnormal test result. Your healthcare provider will consider many factors when interpreting your results and will let you know if you need to undergo further tests to determine the cause of the abnormal level. Don’t be afraid to ask your provider questions. They’re there to help you.
Last reviewed by a Cleveland Clinic medical professional on 11/09/2021.
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