Also known as:Gamma-Glutamyl Transpeptidase; GGTP; Gamma-GT; GTP
Formal name:Gamma-Glutamyl Transferase
Related tests:AST; ALT; ALP; Bilirubin; Liver Panel ; Ethanol
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Why Get Tested?
To evaluate for a possible liver disease or bile duct disease or to differentiate between liver and bone disease as a cause of elevated alkaline phosphatase (ALP); sometimes to screen for or monitor alcohol abuse
When to Get Tested?
When you have symptoms of a liver or bile duct disorder or as follow up when you have an increased ALP level
A blood sample drawn from a vein in your arm
Test Preparation Needed?
GGT levels fall after meals; you may be instructed to fast (nothing to eat or drink except water) for at least 8 hours prior to the test. You may also be asked to stop drinking alcohol or taking certain prescription medications.
How is it used?
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. (Read also about the Liver Panel.) 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.
When is it ordered?
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. A GGT test may be ordered when 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.
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:
- Weakness, fatigue
- Loss of appetite
- Nausea and vomiting
- Abdominal swelling and/or pain
- Dark urine, light-colored stool
- Itching (pruritus)
GGT may also be ordered when someone with a history of alcohol abuse has completed alcohol treatment in order to monitor compliance with the treatment program.
What does the test result mean?
An elevated GGT level suggests that a condition or disease is damaging the liver but does not indicate specifically what. In general, the higher the level, the greater the 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.
Is there anything else I should know?
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.
What is being tested?
Gamma-glutamyl transferase (GGT) is an enzyme that is found in many organs throughout the body, with the highest concentrations found in the liver. GGT is elevated in the blood in most diseases that cause damage to the liver or bile ducts. This test measures the level of GGT in a blood sample.
Normally, GGT is present in low levels, but when the liver is injured, the GGT level can rise. GGT is usually the first liver enzyme to rise in the blood when any of the bile ducts that carry bile from the liver to the intestines become obstructed, for example, by tumors or stones. This makes it the most sensitive liver enzyme test for detecting bile duct problems.
However, the GGT test is not very specific and is not useful in differentiating between various causes of liver damage because it can be elevated with many types of liver diseases, such as liver cancer and viral hepatitis, as well as other non-hepatic conditions, such as acute coronary syndrome. For this reason, the GGT test is not recommended for routine use by itself. However, it can be useful in conjunction with other tests and in determining the cause of a high alkaline phosphatase (ALP) level, another enzyme found in the liver.
Both GGT and ALP are increased in liver diseases, but only ALP will be increased with diseases affecting bone tissue. Therefore, GGT can be used as a follow up to an elevated ALP to help determine if the high ALP result is due to liver or bone disease.
GGT levels are sometimes increased with consumption of even small amounts of alcohol. Higher levels are found more commonly in chronic heavy drinkers than in people who consume less than 2 to 3 drinks per day or who only drink heavily on occasion (binge drinkers). The GGT test may be used in evaluating someone for acute or chronic alcohol abuse.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
GGT levels fall after meals. You may be instructed to fast (have nothing to eat or drink except water) for at least 8 hours prior to the test. Alcohol and certain prescription medications can affect GGT levels, so you may be asked to abstain from them prior to the test as well.
- Can my GGT level be elevated if I don't have any symptoms?
Yes, GGT is very sensitive and can be increased when you don't have symptoms. This elevation may be temporary, perhaps due to medications that you are taking or alcohol ingested within 24 hours of the test. If other liver enzymes are normal, your healthcare practitioner may just wait and then repeat the GGT test. If the GGT is very high and/or your other liver enzymes are elevated, it may be necessary to have more extensive testing to identify the cause.
- I am an alcoholic, but I have quit drinking. Will my GGT ever go back to normal?
Over time, your GGT level will fall from whatever level it was at when you stopped drinking alcohol to within the normal range. This can take several weeks to more than a month. Abstaining from alcohol will decrease your chances of further damaging your liver and should allow your liver function to improve.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.