Gamma-glutamyl transferase, also known as GGT, is an enzyme mainly found in the liver. It helps transport amino acids and peptides into cells and catalyses glutathione, the body's main antioxidant. Since GGT is mainly found in liver cells, its levels are typically measured when there could is danger of damage or disease to the liver. Abnormal GGT levels are typically exhibited in individuals suffering from alcoholism, diabetes, brain tumours, obesity, gallbladder disease and bile-duct obstruction.
GGT and Fatty Liver
Since GGT has high sensitivity in the liver, it is one of the best markers of chronic alcohol consumption and fatty liver. Alcoholism and obesity, among others, are major contributors toward fatty liver. Alcoholic fatty liver, as well as non-alcoholic fatty liver, can progress to more advanced liver disease including inflammation, cirrhosis and liver cancer. Besides fatty liver, increased activity of GGT enzyme can also be observed under medical treatment and in acute pancreatitis, myocardial infraction, anorexia, hyperthyroidism, muscle diseases and neurological disorders. Serum GGT activity is not only influenced by the amount of alcohol consumed but also BMI (body mass index) and gender.
GGT and Heart Disease
In a 2005 report published in "Circulation: Journal of the American Heart Association," researchers cited the GGT test as one of the simplest ways to determine whether or not individuals are at risk of death from cardiovascular disease. Researchers analysed data from a long-term study of 160,000 Austrian adults and found that the higher a person's blood level of GGT, the greater the risk of cardiovascular death.
GGT and Liver Function Tests
According to Dr. David E. Johnson, Associate Professor of Medicine in the Division of Gastroenterology at the University of New Mexico, a number of pitfalls can be encountered in the interpretation of common blood liver tests such as that of GGT levels. Johnson asserts that asymptomatic patients with isolated and mild elevations of GGT levels usually do not have liver disease. As such, they would generally not require extensive tests.
GGT Test and Levels
Measurement of the GGT enzyme is easy and inexpensive. It requires no preparation and involves a blood sample taken from the vein in the forearm. According to the "Circulation: Journal of American Heart Association" report, the normal low level for females is less than 9 U/L, while that of men is less than 14 U/L. The moderate level for females is 18 U/L, while that of males is 28 U/L. High level is more than 36 U/L for females and more than 56 U/L for males. Obesity increases the chances of elevated GGT levels.
Tips and Warnings
Certain medicines used to control seizures such as carbamazepine (Tegretol), phenobarbital, and phenytoin (Dilantin) may cause abnormal GGT levels.
GGT levels are normally elevated in persons who consume three or more alcoholic drinks per week (45g of ethanol or more).
A mildly elevated GGT level is a typical finding in patients who take anticonvulsants (medications for epilepsy).