GGT
At a Glance
Why Get Tested?
To differentiate between liver and bone disease as a cause for elevated alkaline phosphatase (ALP); sometimes to help detect liver disease and/or alcohol abuse
When to Get Tested?
When you have symptoms of a liver disorder or as follow up when you have an increased ALP level
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
GGT levels fall after meals, so it is best to be tested when you have not eaten for at least 8 hours.
The Test Sample
What is being tested?
This test measures the level of gamma-glutamyl transferase (GGT) in the blood. GGT is an enzyme found in many organs, such as the kidney, liver, spleen and pancreas; however, the main source of GGT in the blood is the liver.
GGT is increased in most diseases that cause acute damage to the liver or bile ducts but is usually not helpful in distinguishing between different causes of liver damage. For this reason, use of GGT is controversial, and guidelines published by the National Academy of Clinical Biochemistry and the American Association for the Study of Liver Diseases do not recommend routine use of GGT. These guidelines suggest that it can be useful in determining the cause of a high alkaline phosphatase (ALP), another liver enzyme.
GGT levels in the blood are very sensitive to changes in liver function. 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 in 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 cancer and viral hepatitis as well as other non-hepatic conditions such as acute coronary syndrome.
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 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, so it is best to be tested when you have not eaten for at least 8 hours.
The Test
How is it used?
Gamma-glutamyl transferase (GGT) levels may be used to determine the cause of an 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. If the GGT level is normal in a person with a high ALP, 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 ALT, AST, ALP, and bilirubin. Increased levels of GGT levels may indicate in general that the liver is being damaged but does not specifically point to a condition that may be causing the injury. While elevated GGT levels may be caused by liver disease, they may also be caused by alcohol consumption and/or other conditions, such as congestive heart failure.
GGT can be used to screen for chronic alcohol abuse (it will be elevated in about 75% of chronic drinkers). Sometimes it may be used 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 order alone or as part of a routine liver panel to screen for liver damage even if no symptoms are present. If 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, then a GGT test may be ordered to help determine whether the source of the high ALP is a bone disorder or liver disease.
GGT may be ordered along with or as follow up to other liver function tests when a person has signs or symptoms that suggest liver disease. Some signs and symptoms of liver injury include:
- Weakness, fatigue
- Loss of appetitie
- Nausea and vomiting
- Abdominal swelling and/or pain
- Jaundice
- Dark urine, light colored stool
- Itching (pruritus)
GGT is increased in most diseases that cause acute damage to the liver or bile ducts but is usually not helpful in distinguishing between different causes of liver damage. For this reason, use of GGT is controversial, and guidelines published by the National Academy of Clinical Biochemistry and the American Association for the Study of Liver Diseases do not recommend routine use of GGT. These guidelines suggest that it can be useful in determining the cause of a high ALP.
GGT may be ordered when people with a history of alcohol abuse have completed alcohol treatment to monitor compliance with the treatment program.
What does the test result mean?
Elevated GGT levels may indicate that something is damaging the liver but not specifically what. In general, the higher the level the greater the "insult" to the liver. Elevated levels may be due to liver disease, but they may also be due to other conditions, such as congestive heart failure and alcohol consumption. A high GGT level would help rule out the cause of an increased ALP as a bone disorder.
If GGT is low or normal, then an increased ALP is more likely to be due to bone disease. A low or normal result would also indicate that it is unlikely that a person has liver disease or consumed any alcohol.
Is there anything else I should know?
Even small amounts of alcohol within 24 hours of your GGT test may cause a temporary increase in the GGT. If this occurs, your doctor may want to repeat the test.
GGT levels may be elevated in heart failure. 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 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.
Smoking can also increase GGT.
Levels of GGT increase with age in women, but not in men, and are always somewhat higher in men than in women.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006 Pg 613.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp. 259-260.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry. AACC Press, Washington, DC, Pg. 271.
Carey, W (January 1, 2009). Approach to the Patient with Liver Disease: A Guide to Commonly Used Liver Tests, Cleveland Clinic. Available online at http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/hepatology/guide-to-common-liver-tests/ through http://www.clevelandclinicmeded.com. Accessed September 2009.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson RA and Pincus MR, eds. Philadelphia: 2007, Pp 86, 275.
(2000) Dufour, DR et al. National Academy of Clinical Biochemistry Standards of Laboratory Practice: Laboratory Guidelines for Screening, Diagnosis and Monitoring of Hepatic Injury. Available online at http://www.aacc.org/SiteCollectionDocuments/NACB/LMPG/hepatic/hepatic_combined.pdf#page=3 through http://www.aacc.org.
National Digestive Diseases Information Clearinghouse, part of NIDDK, NIH. NSAIDS and Peptic Ulcers. Available online at http://digestive.niddk.nih.gov/ddiseases/pubs/nsaids/ through http://digestive.niddk.nih.gov. Accessed September 20, 2010.
MedlinePlus Medical Encyclopedia: Gamma-glutamyl transpeptidase. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003458.htm. Accessed September 20, 2010.
Sources Used in Previous Reviews
Mayo 2001 Test Catalog, Mayo Medical Laboratories, Rochester, MN, 2000 Mayo Press.
Worman, H (1998). Common Laboratory Tests in Liver Diseases. Columbia University Health Sciences. Available online at http://cpmcnet.columbia.edu/dept/gi/labtests.html through http://cpmcnet.columbia.edu.
Johnston, D (April 15, 1999). Special Considerations in Interpreting Liver Function Tests. American Family Physician: American Academy of Family Physicians. Available online at http://www.aafp.org/afp/990415ap/2223.html through http://www.aafp.org.
Riley, T (November 1, 2001). Preventive Strategies in Chronic Liver Disease: Part I. Alcohol, Vaccines, Toxic Medications and Supplements, Diet and Exercise. American Family Physician: American Academy of Family Physicians. Available online at http://www.aafp.org/afp/20011101/1555.html through http://www.aafp.org.
British Liver Trust Information Service (Last update September, 10 2001). Cirrhosis. British Liver Trust. Available online at http://www.britishlivertrust.org.uk/publications/cirrhosis.html through http://www.britishlivertrust.org.uk.
MEDLINEplus (October 3, 2001). Medical Encyclopedia: ESR. U.S. National Library of Medicine, Bethesda, MD. MEDLINEplus. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003638.htm.
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (1999). Mosby's Diagnostic and Laboratory Test Reference 4th Edition: Mosby, Inc., Saint Louis, MO.
Dufour DR, et al. Diagnosis and monitoring of hepatic injury - I. Characteristics of laboratory tests. Clin Chem 2000; 46:2027-2049.
