Gamma-glutamyl transferase (GGT) is an enzyme (protein) found in the liver and bile ducts.
A high GGT level in the blood indicates a liver impairment, but it does not specify which type (hepatitis, cirrhosis, bile duct disease, etc.). Generally speaking, the more severe the liver impairment, the higher the GGT levels. Other conditions can also cause high GGT levels, such as congestive heart failure, diabetes, pancreatitis, alcoholism, as well as the ingestion of a number of drugs.
A low or normal GGT level indicates that liver impairment is very unlikely or that the person has not consumed any alcohol recently. Drinking even small amounts of alcohol can raise GGT levels, which is why this test is often used to monitor alcoholism.
If combined with a high alkaline phosphatase level, a high GGT level indicates liver impairment, while a normal GGT level generally indicates that the high alkaline phosphatase level is more likely due to bone disease.
Medications that can raise GGT levels include DilantinTM, carbamazepine and phenobarbital, nonsteroidal anti-inflammatory drugs (NSAIDs), cholesterol medications, and so on.