Doctors use the gamma-glutamyl transferase (GGT) test to diagnose liver problems. They measure GGT if they suspect damage to the liver, bile ducts, chronic alcohol use, or certain bone diseases.

In the GGT test, a healthcare professional measures the levels of GGT in a sample of blood. High levels of GGT can indicate damage to the liver or bile ducts. When GGT falls within the typical range, it suggests that there is no liver damage.

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.

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

  • 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

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

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The test should take less than 5 minutes. During the test, the healthcare professional ties a band around the upper arm, cleans the inner elbow thoroughly with an alcohol pad, and inserts a small needle into the skin. They then collect a small tube of blood.

After the test is complete, 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.

Typically, a person does not need any special preparations for a GGT test.

In some cases, the doctor may ask the person to fast for at least 8 hours before.

GGT is very sensitive and may temporarily elevate if the person takes certain medications or drinks alcohol. The doctor may ask the person to avoid these 24 hours before testing the GGT levels.

A typical range for GGT levels in adults and children is between 0 and 30 international units per liter (IU/L). Newborn infants have significantly higher levels of GGT right after birth.

Typical GGT levels are not concerning to a doctor. 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.

Symptoms of liver damage

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

  • jaundice, which causes yellow skin, eyes, or mucous membranes
  • dark urine
  • nausea
  • vomiting
  • abdominal pain
  • light-colored stool

Causes of liver damage

Some conditions that can cause liver damage include:

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

Liver or 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.

It is a very sensitive liver enzyme test. The GGT test is also part of a series of tests known as a liver panel or liver blood tests, which check the levels of other liver enzymes.

Other liver enzyme levels that doctors check are alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP). This panel of blood tests can also check the levels of proteins, and bilirubin, a waste product of the liver.

Someone with an elevated ALP level may need a GGT test to narrow down the cause.

Bone disease and liver or bile duct disease can lead to elevated ALP levels. A GGT test can help distinguish between these disease types: a typical GGT level likely indicates a bone issue, while a high GGT level may signal a problem with the liver or bile ducts.

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.

Having a blood test is a very safe procedure.

Some people may experience bruising at the needle insertion site after the test. It is also normal to feel a little sore for a short time after the test.

Occasionally, a person may feel faint or anxious during the test, causing them to blackout or pass out. Though this can be frightening, it does not indicate a serious reaction.

Overall, a person’s outlook can depend on the causes of elevated GGT levels.

Doctors can treat the underlying cause of liver disease and prevent further damage to the liver with medication. They might also recommend that people avoid alcohol and certain drugs (both illegal and prescription). If the doctor suspects liver failure, they can consider a transplant.

Learn more about liver disease, including treatment options and prognosis here.

Gamma-glutamyl transferase test (GGT) is a blood test that a doctor may order to assess damage to the liver or bile ducts. However, because this test cannot diagnose the underlying cause, GGT normally form part of a series of tests to help with diagnosing certain diseases.

A typical range for GGT is 0–30 IU/L, although newborn babies may have significantly higher levels.

Individuals may have raised GGT because of:

  • liver damage
  • alcohol use disorder
  • diabetes
  • liver problems
  • congestive heart failure
  • side effects of some medications.

If a person has high GGT results, their doctor typically orders additional testing.