The gamma-glutamyl transpeptidase (GGT) test measures the amount of the enzyme GGT in your blood. Enzymes are molecules that are necessary for chemical reactions in your body. GGT functions in the body as a transport molecule, helping to move other molecules around the body. It plays a significant role in helping the liver metabolize drugs and other toxins. GGT is concentrated in the liver, but is also present in the gallbladder, spleen, pancreas, and kidneys. GGT blood levels are usually high when the liver is damaged.
This test is often done in conjunction with other tests that measure liver enzymes.
The liver is crucial for producing proteins in the body and filtering out poisons. It also makes bile, a substance that helps the body process fats.
Your doctor may order the GGT if he or she suspects your liver is damaged. Often, this stems from heavy use of alcohol or other toxic substances, like drugs or poisons.
Symptoms of liver problems include:
- decreased appetite
- vomiting or nausea
- lack of energy
- abdominal pain
- jaundice (a yellowing of the skin)
- unusually dark urine or light-colored feces
- itchy skin
If you have finished an alcohol rehab program and are trying to abstain from alcohol, your doctor might order this test to check compliance with your treatment program. The test can also monitor levels for people who have been treated for alcoholic hepatitis.
Your doctor may instruct you to fast for eight hours before the test and to stop taking certain drugs. Phenobarbital, phenytoin, and alcohol can raise your GGT level. Birth control pills and clofibrate may decrease your GGT level. If you drink even a small amount of alcohol within 24 hours of the test, it can affect your results.
Your GGT level is measured through a regular blood test. Usually, blood is drawn from inside the elbow. The health worker will put an elastic band around your arm to make your veins more prominent. Then, they will draw blood through a syringe and collect it in a vial for analysis. You may feel a sting or a prick when the needle is inserted. Later, there could be throbbing and a small bruise.
Results for the GGT test should be available the following day. The normal range for GGT in your blood is 0 to 51 international units/liter.
The GGT test is somewhat equivocal, because while it can diagnose liver damage, it can’t determine the cause. If your GGT is elevated, you’ll probably have to undergo more tests.
Some of the conditions that result in increased GGT include:
- overuse of alcohol
- lack of blood flow to the liver
- liver tumors
- cirrhosis (scarred liver)
- overuse of drugs or other toxins
- heart failure
GGT is often measured relative to another enzyme, alkaline phosphatase (ALP). If both are elevated, doctors will suspect problems with the liver or the bile ducts. If GGT is normal and ALP is elevated, this could indicate bone disease. Therefore, the GGT test may be used to rule out certain problems when making a diagnosis.
GGT is sensitive to fluctuations. If your doctor thinks your temporary use of medications or alcohol is affecting the test, he or she might want you to be tested again. Smoking may also increase your GGT level.
If you have recently stopped drinking heavily, it can take more than a month for your GGT to fall to normal levels.
Getting your blood drawn is a low-risk procedure. The size of arteries and veins vary among patients, so some people have an easier time than others do.
Some people are sensitive to needles and may feel faint. There’s a chance of slight bleeding at the insertion site or of getting a hematoma, a blood bruise under the skin. Infection occurs in rare cases.