OVERVIEW

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.