Gamma-glutamyl transferase

The GGT test helps to detect liver disease and bile duct injury. Doctors can also use the test to help find out the reason for a raised level of alkaline phosphatase (ALP). Both ALP and GGT are elevated in disease of the bile ducts and in some liver diseases, but only ALP will be elevated in bone disease. If the GGT level is normal in a person with a high ALP, the cause is most likely to be bone disease. GGT can also be used to screen for alcohol abuse (it will be elevated in about 75% of long-term heavy drinkers).

A doctor usually requests GGT along with other tests to evaluate a person who has signs or symptoms that suggest liver disease. Some of the symptoms of liver injury include jaundice, nausea, vomiting, abdominal (around the stomach area) swelling, abdominal pain, pruritus (severe itching), and tiredness.

GGT is increased in most diseases that cause damage to the liver or bile ducts, but is usually not helpful in distinguishing between different causes of liver damage. GGT is also useful in determining the cause of a high ALP. In people with a history of alcohol abuse who are undergoing treatment, GGT may be used to check that the person is following the treatment program properly.

Your doctor is not usually concerned with low or normal levels, but they do tell him/her that it is unlikely that you have liver disease.

Raised GGT levels indicate that something is going on with your liver but not specifically what. In general, the higher the level the greater the damage to your liver. Elevated levels may be due to liver disease, but they may also be due to congestive heart failure, drinking alcohol, and use of many prescription and non-prescription drugs including nonsteroidal anti-inflammatory drugs (NSAIDs), lipid-lowering drugs, antibiotics, histamine blockers (used to treat excess stomach acid production), antifungal agents, anticonvulsants (seizure control medications), antidepressants, and hormones such as testosterone. Oral contraceptives (birth control pills) and clofibrate can decrease GGT levels.

Even small amounts of alcohol within 24 hours of your GGT test may cause a temporary increase in the GGT. If this occurs, your doctor may want to repeat the test to verify that it is normal.

GGT levels fall after meals, so it is best to be tested when you have not eaten for at least 8 hours.

GGT is higher in persons of African ancestry than those of European ancestry.

Several drugs increase (induce) the concentration of GGT in the blood. The increases do not indicate damage to the liver and can be considered an interference.