The gamma-glutamyl transferase (GGT) test may be used to determine the cause of elevated 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. Therefore, if the GGT level is normal in a person with a high ALP, the cause of the elevated ALP is most likely bone disease.
The GGT test is sometimes used to help detect liver disease and bile duct obstructions. It is usually ordered in conjunction with or as follow up to other liver tests such as ALT, AST, ALP, and bilirubin. In general, an increased GGT level indicates that a person's liver is being damaged but does not specifically point to a condition that may be causing the injury.
GGT can be used to screen for chronic alcohol abuse (it will be elevated in about 75% of chronic drinkers) and to monitor for alcohol use and/or abuse in people who are receiving treatment for alcoholism or alcoholic hepatitis.
A GGT test may be ordered when someone has an elevated ALP level. An ALP test may be ordered alone or as part of a routine liver panel to screen for liver damage even if no symptoms are present. If results of the ALP test are high but other tests that are part of the liver panel (such as AST and ALT) are not increased, then a GGT test may be ordered to help determine whether the source of the high ALP is a bone disorder rather than liver disease.
GGT may be ordered along with or as a follow up to other liver function tests when a person has signs or symptoms that suggest liver disease. Some signs and symptoms of liver damage include:
An elevated GGT level suggests that something is damaging the liver but does not indicate specifically what. In general, the higher the level, the greater the "insult" – or damage – to the liver. Elevated levels may be due to liver diseases, such as hepatitis or cirrhosis, but they may also be due to other conditions, such as congestive heart failure, diabetes, or pancreatitis. They may also be caused by alcohol abuse or use of drugs that are toxic to the liver.
A low or normal GGT test result indicates that it is unlikely that a person has liver disease or has consumed any alcohol.
A high GGT level can help rule out bone disease as the cause of an increased ALP level, but if GGT is low or normal, then an increased ALP is more likely due to bone disease.
Even small amounts of alcohol within 24 hours of a GGT test may cause a temporary increase in the GGT.
Smoking can also increase GGT.
Elevated GGT levels may be an indicator of cardiovascular disease and/or hypertension. Some studies have shown that people with increased GGT levels have an elevated risk of dying from heart disease, but the reason for this association is not yet known.
Drugs that may cause an elevated GGT level include phenytoin, carbamazepine, and barbiturates such as phenobarbital. Use of many other prescription and non-prescription drugs, including nonsteroidal anti-inflammatory drugs (NSAIDs), lipid-lowering drugs, antibiotics, histamine receptor blockers (used to treat excess stomach acid production), antifungal agents, antidepressants, and hormones such as testosterone, can increase GGT levels. Clofibrate and oral contraceptives can decrease GGT levels.
Levels of GGT increase with age in women, but not in men, and are always somewhat higher in men than in women.
This article was last reviewed on October 30, 2013. | This article was last modified on February 23, 2015.
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