At a Glance
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.
The Test Sample
What is being tested?
Gamma-glutamyl transferase (GGT) is an enzyme that is found in many organs, such as the kidney, liver, gallbladder, spleen, and pancreas. Among these, the liver is the main source of GGT in the blood. This test measures the level of GGT in a blood sample.
GGT is increased in most diseases that cause damage to the liver or bile ducts. 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 cancer and viral hepatitis as well as other non-hepatic conditions such as acute coronary syndrome.
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 do suggest, however, that it can be useful 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.
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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
Gamma-glutamyl transpeptidase. (Updated Jan. 21, 2013.) MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003458.htm. Accessed September 2013.
Kim, KM et al. (Dec. 2012) Serum gamma-glutamyltransferase as a risk factor for general cardiovascular disease prediction in Koreans. National Center for Biotechnology Information PubMed database. Available online at http://www.ncbi.nlm.nih.gov/pubmed/23138005 through http://www.ncbi.nlm.nih.gov/pubmed. Accessed September 2013.
Gamma-glutamyltransferase level and risk of hypertension: a systematic review and meta-analysis. PLOS. Available online through http://www.plosone.org at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0048878 through http://www.plosone.org. Accessed September 2013.
Ghadban, R. et. al. (Updated Aug. 2, 2012). Gamma-Glutamyltransferase. Medscape. Available online at http://emedicine.medscape.com/article/2087891-overview#aw2aab6b3 through http://emedicine.medscape.com. Accessed September 2013.
KidsHealth. Blood Test: Gamma-Glutamyl Transpeptidase (GGT). Available online at http://kidshealth.org/parent/system/medical/test_ggt.html through http://kidshealth.org. Accessed September 2013.
George, Hank. GGT - Gammaglutamyl Transferase. December, 2000. Available online at http://www.stat.unc.edu/visitors/temp/Health/Thyroid/ggt2.htm through http://www.stat.unc.edu. Accessed September 2013.
General Practice Notebook. GGT and alcohol intake. Available online at http://www.gpnotebook.co.uk/simplepage.cfm?ID=x20080405181818225450 through http://www.gpnotebook.co.uk. Accessed September 2013.
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.
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.