The gamma-glutamyl transpeptidase (GGT) test measures the amount of the enzyme in your blood. It is often measured relative to alkaline phosphatase (ALP) to determine if you may have problems with your liver, bile ducts, or bones.
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 it’s 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 with other tests that measure liver enzymes if there’s a possibility of liver damage. Read more about other liver function tests.
Your liver is crucial for producing proteins in your body and filtering out poisons. It also makes bile, a substance that helps your body process fats.
Your doctor may order the GGT test if they suspect your liver is damaged or if you have a liver disease, particularly if it’s related to alcohol use. The GGT test is currently the most sensitive enzymatic indicator of liver damage and disease. This damage is often caused by heavy use of alcohol or other toxic substances, like drugs or poisons.
The symptoms of liver problems include:
- decreased appetite
- nausea or vomiting
- lack of energy
- abdominal pain
- jaundice, which is a yellowing of the skin
- unusually dark urine
- light-colored feces
- itchy skin
If you’ve finished an alcohol rehabilitation program and you’re trying to abstain from alcohol, your doctor might order this test to check that you’re following the treatment program. The test can also monitor GGT 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 medications. If you drink even a small amount of alcohol within 24 hours of the test, it can affect your results.
A regular blood test can measure your GGT level. Usually, blood is drawn from your arm at the crease of your elbow. The healthcare provider 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. You might feel throbbing and have a small bruise later.
Your results from the GGT test should be available the following day. Your doctor will help you interpret them and assess if they’re in the normal range or not. According to the Mayo Clinic, the normal range for GGT levels is 9–48 units per liter (U/L). Normal values can vary due to age and sex.
The GGT test can diagnose liver damage, but it can’t determine the cause. If your GGT level is elevated, you’ll probably have to undergo more tests. Generally, the higher the GGT level the greater the damage to the liver.
Some of the conditions that result in increased GGT include:
- overuse of alcohol
- chronic viral hepatitis
- lack of blood flow to the liver
- liver tumor
- cirrhosis, or scarred liver
- overuse of certain drugs or other toxins
- heart failure
- fatty liver disease
GGT is often measured relative to another enzyme, alkaline phosphatase (ALP). If GGT and ALP are both elevated, doctors will suspect that you have problems with your liver or the bile ducts. If GGT is normal and ALP is elevated, this could indicate bone disease. Your doctor may use the GGT test in this way to rule out certain problems.
GGT is sensitive to fluctuations. If your doctor thinks your temporary use of medications or alcohol is affecting the test, they might want you to be tested again. Barbiturates, phenobarbital, and some nonprescription drugs can increase the levels of GGT in your body. Levels of GGT increase with age in women, but not in men.
If you have recently stopped drinking heavily, it can take up to a month for your GGT to fall to normal levels. Smoking can also increase your GGT level.
Getting your blood drawn is a relatively low-risk procedure. There’s a chance of slight bleeding at the insertion site or of getting a hematoma — a blood bruise under the skin. Infection only occurs in very rare cases.
Liver damage is serious and can often lead to other health problems. Depending on the extent of the damage, it can also be irreversible. The GGT test, used in conjunction with other testing methods, can help your doctor see if you have liver damage.
Be sure to consult your doctor if you have any symptoms related to liver damage so they can test you, uncover the cause, and get you started on a treatment regimen.
Some studies indicate that high coffee intake may lower GGT level in heavy drinkers, but it may take more than five cups per day. Beware, excessive coffee intake creates its own problems, including high blood pressure and sleep difficulties.
Ultimately, quitting smoking, quitting alcohol, and losing weight are important first steps toward lowering GGT levels and allowing the liver to heal while adopting a more healthful lifestyle.