Gamma-Glutamyl Transferase (GGT) Test

What is gamma-glutamyl transferase (GGT)?

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.

What is a gamma-glutamyl transferase (GGT) blood test?

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.

Your GGT levels can also rise from administration of foreign substances such as medications (like phenobarbital, phenytoin or warfarin) or alcohol.

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:

• Gamma-glutamyl transpeptidase.
• GGTP.
• Gamma-GT.
• GTP.

Why do I need a GGT blood test?

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 have an elevated alkaline phosphatase (ALP) level in your blood.
• If you have signs and symptoms of liver disease or bile duct obstructions.
• To screen for alcohol use disorder or to monitor your compliance to treatment for alcohol abuse (usually sobriety, or abstaining from alcohol).

Elevated ALP levels

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.

Liver disease

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:

• Nausea and/or vomiting.
• Belly (abdominal) pain.
• Itchy skin.
• Jaundice (a yellowing of your skin and the whites of your eyes).
• Tiredness (fatigue).
• Appetite loss.

Alcohol use disorder

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.

Who performs a GGT blood test?

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.

Do I need to do anything to prepare for a GGT blood test?

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.

What should I expect during my GGT blood test?

You can expect to experience the following during a blood test, or blood draw, which includes a GGT test:

• You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
• Once they’ve located a vein, they’ll clean and disinfect the area.
• They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
• After they insert the needle, a small amount of blood will collect in a test tube.
• Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
• They’ll place a bandage over the site, and you’ll be finished.

The entire procedure usually takes less than five minutes.

What should I expect after my GGT blood test?

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.

What are the risks of a GGT blood test?

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.

When can I expect the results of my GGT blood test?

In most cases, you should have your test results within one to two business days, though it could take longer.

What do the results of a GGT blood test mean?

Blood test reports, including gamma-glutamyl transferase (GGT) test reports, usually provide the following information:

• The name of the blood test or what was measured in your blood.
• The number or measurement of your blood test result.
• The normal measurement range for that test.
• Information that indicates if your result is normal or abnormal or high or low.

What is a normal range for a GGT blood test?

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.

What does it mean if my GGT is high?

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:

• Hepatitis (liver inflammation), especially viral hepatitis and alcoholic hepatitis.
• Cirrhosis (scarring of the liver).
• Cholestasis (blocked liver bile duct).
• Alcohol liver disease.
• Non-alcoholic fatty liver disease.
• Liver ischemia (not enough blood flow to your liver, which leads to death of liver tissue).
• Liver tumor or liver cancer.

Other conditions that can cause elevated GGT levels include:

• Alcohol use disorder.
• Pancreatitis or pancreatic cancer.
• Diabetes.
• Congestive heart failure.
• Certain medications that can cause liver damage.

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.

Should I be worried if my GGT is high?

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:

• Consuming alcohol: Even small amounts of alcohol consumed within 24 hours of a GGT test can increase your GGT levels. However, people who frequently drink significant amounts of alcohol commonly have higher levels of GGT than people who consume less than two to three drinks per day or drink heavily on occasion.
• Smoking: Cigarette smoking is significantly associated with increased levels of GGT and ALP.
• Certain medications: Medications that can increase your GGT levels include acetaminophen, carbamazepine, phenytoin, phenobarbital and more.

In addition to the above factors, your healthcare provider will consider many aspects of your health and situation when analyzing your GGT result, including:

• Your medical history.
• How high your GGT results are.
• The results of other tests that are usually taken alongside GGT.
• If you’re experiencing symptoms.

When should I call my doctor?

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.