At a Glance
Why Get Tested?
To detect 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?
Aspartate aminotransferase (AST) is an enzyme found in cells throughout the body but mostly in the heart and liver and, to a lesser extent, in the kidneys and muscles. In healthy individuals, levels of AST in the blood are low. When liver or muscle cells are injured, they release AST into the blood. This makes AST 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 injury to liver cells and may cause increases in AST. The test is most useful in detecting liver damage due to hepatitis, drugs toxic to the liver, cirrhosis, or alcoholism. AST, however, is not specific for the liver and may be increased in conditions affecting other parts of the body.
An AST test is often performed along with an alanine aminotransferase (ALT) test. Both are enzymes found in the liver that become elevated in the blood when the liver is damaged. A calculated AST/ALT ratio is useful for differentiating causes of liver injury and in recognizing when the increased levels may be coming from another source, such as heart or muscle injury.
How is the sample collected for testing?
A blood sample is drawn by needle 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
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.
AST. (Updated Jan. 21, 2013.) MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003472.htm. 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 126-129.
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. Available online at 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 23 2009) MedlinePlus Medical Encyclopedia: AST. Available online at ttp://www.nlm.nih.gov/medlineplus/ency/article/003472.htm. Accessed February 2010.