About the Test
Purpose of the test
The GGT test may be used to determine the cause of elevated ALP. Both ALP and GGT are elevated in diseases of the bile ducts and in some liver diseases, but only ALP will be elevated in bone disease. Therefore, if the GGT level is within the reference range if you have a high ALP result, the cause 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 alanine aminotransferase (ALT), aspartate aminotransferase (AST), ALP, and bilirubin. In general, an increased GGT level indicates that the 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 if you are receiving treatment for alcoholism or alcoholic hepatitis.
What does the test measure?
GGT is an enzyme that is found in many organs throughout the body, with the highest concentrations found in the liver. It 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 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 intestine become obstructed, for example, by tumors or stones. This makes it the most sensitive liver enzyme test for detecting bile duct problems.
But the GGT test is not very specific or useful in differentiating between various causes of liver damage. 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. But 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 result is due to liver or bone disease.
GGT levels are sometimes increased with the consumption of even small amounts of alcohol. Higher levels are found more commonly in chronic heavy drinkers than in people who consume less than two to three 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.
When should I get this test?
A GGT test may be ordered when you have 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. The 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 you have signs or symptoms that suggest liver disease, such as:
- Weakness, fatigue
- Loss of appetite
- Nausea and vomiting
- Abdominal swelling and/or pain
- Jaundice, which is yellowing of the skin and whites of the eyes
- Dark urine, light-colored stool
- Itching (pruritus)
GGT may also be ordered when someone with a history of alcohol abuse has completed alcohol treatment and it is necessary to monitor in compliance with the treatment program.
Finding a Gamma-Glutamyl Transferase (GGT) Test
How can I get a Gamma-Glutamyl Transferase (GGT) Test?
Your doctor may order a GGT test if you have elevated ALP levels, or as part of a routine liver panel to screen for liver damage. GGT testing uses a sample of blood to test for elevated GGT levels in the blood. When prescribed by a doctor, a blood sample may be collected in a hospital or other medical setting and sent to a laboratory for analysis. Blood is usually drawn from a vein in your arm.
Can I take the test at home?
You can find at-home liver tests that screen for GGT, among other proteins, using a finger prick blood test taken before breakfast. Next, you send your sample to a lab using a prepaid envelope for testing. These tests are convenient but may not be as extensive or reliable as a liver panel ordered by your doctor. If your at-home test comes back with an abnormal result, consult with your doctor for confirmatory testing and the next steps.
How much does the test cost?
The cost of GGT testing varies based on many factors. When ordered by a doctor, your health insurance may cover GGT testing. Health plans vary, so if you have health insurance, it’s important to talk to an administrator about the cost of testing, including any copays or deductibles that may be required.
If you don’t have health insurance coverage that covers GGT testing, it may be helpful to discuss the cost of testing with a doctor. The total cost can include the office visit, the blood draw, and technician fees in addition to the price of laboratory testing.
Taking a Gamma-Glutamyl Transferase Test
A GGT test is performed on a blood sample taken from a vein in your arm, which will be collected in a laboratory or medical facility.
Before the test
GGT levels fall after meals, so you may be instructed to fast (nothing to eat or drink except water) for at least eight hours prior to the test. You may also be asked to stop drinking alcohol or taking certain prescription medications beforehand.
During the test
During a blood draw, a health care provider takes a sample of blood from a vein in your arm. After locating an appropriate vein and cleaning the collection site, a small needle is inserted into the vein, and blood is collected in an attached vial. A blood draw usually takes less than five minutes.
After the test
After a blood sample is collected, a bandage or piece of gauze may be applied to reduce additional bleeding. Risks of blood collection are minimal, although you may have light bruising and tenderness where the needle was inserted. There are no restrictions on normal activities after a blood sample is collected.
Gamma-Glutamyl Transferase Test Results
Receiving test results
GGT test results may be available within a few business days after the laboratory receives your blood sample. Results may be available online or through your doctor. You may need to schedule a follow-up appointment with your doctor to get them in person. Some providers also give test results by phone or postal mail.
Interpreting test results
Results of the GGT are interpreted along with ALP and other test results that may have been performed at the same time, such as a liver panel.
An elevated ALP with a high GGT level helps rule out bone disease as the cause of the increased ALP level. If you have an elevated ALP with a low or normal GGT it means the increased ALP is more likely due to bone disease.
An elevated GGT level suggests that a condition or disease is damaging the liver but does not indicate specifically the cause of the damage. In general, the higher the level, the greater the damage.
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, metabolic syndrome, diabetes, or pancreatitis, which is inflammation of the pancreas. They may also be caused by alcohol abuse, alcoholic liver disease, or the use of drugs that are toxic to the liver.
A low or normal GGT test result indicates that it is unlikely that you have liver disease or have consumed any alcohol.
GGT is very sensitive and can be increased when you don’t have symptoms. This may be temporary, perhaps due to medications you are taking or if you drink alcohol within 24 hours of the test. If other liver enzymes are normal, your health care practitioner may repeat the GGT test at a later date. If the GGT is very high and/or your other liver enzymes are elevated, you may need additional testing to identify the cause.
Even small amounts of alcohol within 24 hours of a GGT test may cause a temporary increase in the GGT. However, genetic variability between individuals can cause differences in this response of GGT to alcohol use. Smoking can also increase GGT.
Elevated GGT levels may be an indicator of cardiovascular disease and/or hypertension. Some studies have shown that if you have increased GGT levels you have an elevated risk of dying from heart disease, but the reason for this association is not yet known.
Low levels of GGT are observed in certain genetic diseases where the flow of bile from the liver is interrupted or suppressed.
Drugs that may cause an elevated GGT level include:
- Phenytoin, carbamazepine, and barbiturates such as phenobarbital
- 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, oral contraceptives and hormones such as testosterone
- Certain anticoagulants (e.g., heparin) and immunosuppressive medications (e.g., methotrexate) also increase GGT levels in serum
Levels of GGT increase with age in women, but not in men, and are always somewhat higher in men than in women.
You may want to ask your doctor some follow-up questions, such as:
- Were any of the measurements on my test abnormal? If so, which ones?
- What might explain any abnormal results?
- Based on my GGT results, are there any other tests that you recommend?
- Should I have the GGT test again? If so, when should it be done?
- MedlinePlus: Liver Diseases
- American Liver Foundation: Resources
- MayoClinic.org: Alcohol Use Disorder
- National Institute on Alcohol Abuse and Alcoholism: Rethinking Drinking
- National Institute of Diabetes and Digestive and Kidney Diseases: Liver Disease
- KidsHealth.org: Pancreatitis
- MedlinePlus: Pancreatitis
- National Institute of Diabetes and Digestive and Kidney Diseases: Pancreatitis