At a Glance
Why Get Tested?
To screen for liver damage and/or to help diagnose liver disease
When to Get Tested?
When a health practitioner thinks that you have symptoms of a liver disorder
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Alanine aminotransferase (ALT) is an enzyme found mostly in the cells of the liver and kidney. Much smaller amounts of it are also found in the heart and muscles. In healthy individuals, ALT levels in the blood are low. When the liver is damaged, ALT is released into the bloodstream, usually before more obvious signs of liver damage occur, such as jaundice. This makes ALT a useful test for detecting liver damage.
The liver is a vital organ located in the upper right-hand side of the abdominal area. It is involved in many important functions in the body. The liver helps to process the body's nutrients, manufactures bile to help digest fats, produces many important proteins such as blood clotting factors, and breaks down potentially toxic substances into harmless ones that the body can use or excrete.
A number of conditions can cause damage to liver cells, resulting in an increase in ALT. The test is most useful in detecting damage due to hepatitis or as a result of drugs or other substances that are toxic to the liver.
ALT is commonly tested in conjunction with aspartate aminotransferase (AST), another liver enzyme, as part of a liver panel. Both ALT and AST levels usually rise whenever the liver is being damaged, although ALT is more specific for the liver and, in some cases, may be the only one of the two to be increased. An AST/ALT ratio may be calculated to aid in distinguishing between causes and severity of liver injury and to help distinguish liver injury from damage to heart or muscles.
How is the sample collected for testing?
A blood sample is drawn from 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?
No test preparation is needed.
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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
Alanine Aminotransferase (ALT) (GPT), Serum. Mayo Clinic. Available online at http://www.mayomedicallaboratories.com/test-info/hematology/catalog/Overview/8362 through http://www.mayomedicallaboratories.com. Accessed September 2013.
Orlewicz, M. S. (Update April 20, 2012.) Alanine Aminotransferase. Medscape. Available online at http://emedicine.medscape.com/article/2087247 through http://emedicine.medscape.com. Accessed September 2013.
Nyblom, H. et. al. (July 2004.) High AST/ALT Ratio May Indicated Advanced Alcoholic Liver Disease Rather Than Heavy Drinking. National Center for Biotechnology Information PubMed. Available online at http://www.ncbi.nlm.nih.gov/pubmed/15208167 through http://www.ncbi.nlm.nih.gov/pubmed. Accessed September 2013.
Sources Used in Previous Reviews
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby; 1998.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006, Pp 604-606.
Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005) Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 1811-1815.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 40-42.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC, Pp 270-271.
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 February 2010.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson RA and Pincus MR, eds. Philadelphia: 2007, Pp 268-269.
(2000) Dufour, DR et al. National Academy of Clinical Biochemistry Standards of Laboratory Practice: Laboratory Guidelines for Screening, Diagnosis and Monitoring of Hepatic Injury http://www.aacc.org/SiteCollectionDocuments/NACB/LMPG/hepatic/hepatic_combined.pdf#page=3 through http://www.aacc.org. Accessed February 2010.
(March 15, 2005) Giboney, P. Mildly Elevated Liver Transaminases in the Asymptomatic Patient. Am Fam Physician 2005; 71:1105–10. Available online at http://www.aafp.org/afp/2005/0315/p1105.html through http://www.aafp.org. Accessed February 2010.
(Feb 22, 2009) MedlinePlus Medical Encyclopedia: ALT. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003473.htm. Accessed February 2010.