Doctors use the gamma-glutamyl transferase (GGT) blood test to diagnose liver problems. High levels of GGT can indicate damage to the liver or bile ducts, or other conditions.

A typical range for GGT levels in adults and children is between 0 and 50 international units per liter (IU/L).

With the GGT test, a healthcare professional measures the levels of GGT in a sample of blood. When GGT falls within the typical range, it suggests that there is no liver damage.

Read on to learn more about the GGT test, including its purpose, what it involves, and what abnormal GGT ranges can mean.

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The GTT test should take about 5 minutes. During the test, the healthcare professional:

  1. ties a band around the upper arm
  2. cleans the inner elbow thoroughly with an alcohol pad
  3. inserts a small needle into the skin
  4. collect a small tube of blood

After collecting the sample, the healthcare professional will remove the needle and the band. They will also apply pressure to the site to make sure any bleeding stops.

As with any other blood test, the blood draw may cause minor discomfort. This pain should pass quickly.

The healthcare professional labels the sample and sends it to a lab for testing. The lab should produce the results within a day or two, though it may take a little longer for the doctor to receive and interpret the results.

A doctor may order a GGT test for the following reasons:

  • as part of regular blood testing or physical examination
  • if a person is taking a medication that has potentially toxic effects on the liver
  • if a person has symptoms of liver disease
  • monitoring the treatment of people with alcohol use disorder

A GGT test cannot diagnose the cause of any liver problems, so doctors usually also request other liver blood tests, such as an alkaline phosphatase (ALP) test. ALP is another liver enzyme that doctors use to help diagnose bone disorders in addition to liver disease.

Symptoms of liver damage

The symptoms of liver damage can range in severity. Some symptoms can include:

A person does not usually need any special preparations for a GGT test.

However, a person should check with their doctor in case they need to fast before the test, or if they need to avoid anything specific, such as alcohol.

The doctor can also confirm if a person can continue taking any medications as usual.

A typical range for GGT levels is between 6 and 50 international units per liter (IU/L). However, reference ranges can be different for each laboratory. For example, the United Kingdom’s National Health Service (NHS) suggests that a typical range is between 15 and 40 UI/L.

Newborn infants have significantly higher levels of GGT right after birth.

A person with a GGT level within the expected range probably does not have liver disease.

The liver contains the highest levels of GGT, while the blood and some other organs contain minimal quantities.

High levels of GGT in the blood could indicate that the enzyme is leaking out of the liver cells and into the blood. This may suggest that there is damage to the liver or bile ducts. GGT levels rise according to the amount of liver damage a person has.

High GGT levels could indicate liver damage, though it does not diagnose the specific cause. A person often needs follow-up tests to determine the reasons for the elevated GGT levels.

GGT levels may increase for many reasons. A doctor may request other tests in conjunction with a GGT test to diagnose liver disease or determine the underlying cause.

Liver damage

Liver damage can cause high GGT levels.

Some conditions that can cause liver damage include:

Exposure to toxins and taking some medications may also cause liver damage.

Bile duct damage

GGT is a useful marker for detecting bile duct injury. GGT levels usually rise when a person has a bile duct obstruction.

Alcohol use disorder

GGT levels tend to be higher in people who regularly drink alcohol, compared with people who drink in moderation or only on occasion. Because of this, a doctor may measure GGT levels to test for alcohol use disorder.

Doctors may use the test to monitor alcohol use in someone receiving treatment for alcohol use disorder or hepatitis due to chronic alcohol use.

A blood test is a safe procedure.

Some people may experience bruising at the needle insertion site after the test. A person may also feel a little sore for a short time after the test.

Occasionally, a person may feel dizzy or anxious during the test, causing them to faint. It is important to let the person performing the blood test know if a person feels particularly nervous or lightheaded.

What is an alarming level of GGT?

A high level of GGT can depend on the laboratory performing the test, but anything over 50 IU/L can indicate liver damage. For some laboratories, this number might be lower. For example, the United Kingdom’s NHS suggests that a high level of GGT is over 40 IU/L.

Does GGT mean fatty liver?

Nonalcoholic fatty liver disease may cause high GGT levels. However, there are numerous other possible causes of liver damage and high GGT levels. A doctor will need to order other tests to determine the underlying condition.

A gamma-glutamyl transferase (GGT) test is a blood test that a doctor may order to assess damage to the liver or bile ducts.

The GGT test typically forms part of a series of tests to help with diagnosing certain conditions, such as causes of liver damage or bile duct obstruction. It can also help with monitoring alcohol use disorder.

A typical range for GGT is 6 to 50 IU/L, though this can vary. Newborn babies may have significantly higher levels. A person’s doctor can provide more information about their GGT levels, and whether further tests are necessary.