What is gamma-glutamyl transpeptidase?

Gamma-glutamyl transpeptidase (GGT), is an enzyme that transfers gamma-glutamyl functional groups. Gamma-glutamyl transpeptidase catalyzes the transfer of the gamma-glutamyl moiety of glutathione to an acceptor that may be an amino acid, a peptide or water hence forming glutamate. GGT plays a key role in the gamma-glutamyl cycle, a pathway for the synthesis and degradation of glutathione and drug and xenobiotic detoxification.

Gamma-glutamyl transpeptidase is present in the cell membranes of many tissues including the kidney, bile ducts, pancreas, gallbladder, spleen, heart, brain, seminal vesicles and in small amounts in the blood. It is involved in the transfer of amino acids across the cellular membrane, as well as the leukotriene metabolism.


Why measure the level of gamma-glutamyl transpeptidase?

Gamma-glutamyl transpeptidase is predominantly used as a diagnostic marker for liver disease or bile ducts (tubes that carry bile from the liver to the gallbladder and intestine), this test along with others can be useful to check a patients liver function. The test is also used to check for liver damage related to ingestion of toxic substances or alcohol abuse.

Elevated serum GGT activity can be found in diseases of the liver, biliary system, and pancreas. In this respect, it is similar to alkaline phosphatase (ALP) in detecting disease of the biliary tract. Indeed, the two markers correlate well, though there is conflicting data about whether GGT has better sensitivity. In general, ALP is still the first test for biliary disease. The main value of GGT over ALP is in verifying that ALP elevations are, in fact, due to biliary disease; ALP can also be increased in certain bone diseases, but GGT is not.

Gamma-glutamyl transpeptidase is elevate by large quantities of alcohol ingestion, however high levels of GGT are not always associated with alcohol intoxication, and the measurement of selected serums forms of the enzyme offer more specific information.

Normal values range from 0 to 51 IU/L, however this depends on the laboratory and the test used. Abnormal results may indicate congestive heart failure, cholestasis (congestion of the bile ducts), cirrhosis, hepatitis, liver ischemia (blood flow deficiency), liver necrosis, liver tumor, use of hepatotoxic drugs, death of liver tissues, heart failure, and diabetes


Standard of preparation

Sampling is usually done in the morning in the hospital. There are no special preparations needed for this test. The doctor will advise and recommend if you need to be fasting prior to the blood examination. You should inform your doctor of any medication you are taking prior to the exam, as some medical treatments may interfere with the blood results. There are certain drugs that increase GGT levels, such as that of alcohol consumption, phenytoin, and phenobarbital. However there are also drugs that can reduce GGT levels such as birth control pills and clofibrate.


Is the examination painful or dangerous?

The examination is neither painful nor dangerous. The patient may feel a tingling sensation with the entrance of the needle in the arm when blood is being extracted for examination.


How is the exam performed?

The exam consists of a simple blood sample test.