The GGT test helps to detect liver and bile duct injury. While some doctors use it in all people they suspect of having liver disease, others use it only to help explain the cause of other changes or if they suspect alcohol abuse. For example, 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 bone disease. GGT can also be used to screen for chronic alcohol abuse (it will be elevated in about 75% of chronic drinkers).

A doctor usually orders 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 swelling, abdominal pain, pruritus (severe itching), and fatigue.

GGT is increased in most diseases that cause acute damage to the liver or bile ducts, but is usually not helpful in distinguishing between different causes of liver damage. For this reason, use of GGT is controversial, and guidelines published by the National Academy of Clinical Biochemistry and the American Association for the Study of Liver Diseases do not recommend routine use of GGT. These guidelines suggest that it can be useful in determining the cause of a high ALP. In persons with a history of alcohol abuse who have completed alcohol treatment, GGT may be used to monitor compliance with the treatment program.

Doctors are not usually concerned with low or normal levels, but they do indicate that it is unlikely that a patient has liver disease.

Elevated GGT levels indicate that something is going on with your liver but not specifically what. In general, the higher the level the greater the “insult” to your liver. Elevated levels may be due to liver disease, but they may also be due to congestive heart failure, alcohol consumption, 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, 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.

Smoking can also increase GGT.

Levels of GGT increase with age in women, but not in men, and are always somewhat higher in men than in women.

GGT is about twice as high in persons of African ancestry as in those of European ancestry.