At a Glance
Why Get Tested?
When to Get Tested?
When a patient has hepatitis that the doctor suspects may be due to an autoimmune-related process
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
This test measures the amount of smooth muscle antibodies (SMA) in the blood. SMA are proteins produced by the body’s immune system that are directed against its own cytoskeletal proteins of the smooth muscle. Cytoskeletal proteins form the framework within a cell that serve to support or reinforce the cell structure. The production of SMA is strongly associated with chronic active autoimmune hepatitis but may also be seen in other forms of liver disease and with other autoimmune disorders such as primary biliary cirrhosis, but usually at lower titers. Autoimmune hepatitis presents as an acute or chronic inflammation of the liver that is not a result of another discernable cause – such as a viral infection, drug, toxin, hereditary disorder, or alcohol abuse. It can lead to liver cirrhosis and, in some cases, to liver failure.
Autoimmune hepatitis can be found in anyone at any age, but about 80% of those affected are women. In the United States, more than 70% of patients with this disorder will have SMA, either alone or along with ANA (antinuclear antibodies). F-actin is a specific cytoskeletal protein whereby autoantibodies directed against it may be increased. Some recent studies suggest that it is a more specific test than SMA in diagnosing autoimmune liver disease, with about 52% to 85% of those affected having the F-actin autoantibody.
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?
No test preparation is needed.
Ask a Laboratory Scientist
This form enables you to ask specific questions about your tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. If your questions are not related to your lab tests, please submit them via our Contact Us form. Thank you.
* indicates a required field
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
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 96-97.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 272.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition: Saunders Elsevier, St. Louis, MO. Pp 990-991.
Lee, S. (Updated 2007 May 27). Anti-smooth muscle antibody. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003531.htm. Accessed 1/29/09.
(2008 April). Autoimmune Hepatitis. NDDIC [On-line information]. Available online at http://digestive.niddk.nih.gov/ddiseases/pubs/autoimmunehep/ through http://digestive.niddk.nig.gov. Accessed 1/29/09.
Dugdale, D. (Updated 2008 November 2). Autoimmune liver disease panel. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003328.htm. Accessed 1/29/09.
Hill, H. et. al (Updated 2008 September). Hepatitis, Autoimmune – AIH. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/GastrointestinalDz/AIH.html# through http://www.arupconsult.com. Accessed 1/29/09.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 92-93.
Beuers, U. and Rust, C. (2005 October 27). Overlap Syndromes. Medscape, from Semin Liver Dis. 2005; 25(3): 311-320. [On-line information]. Available online at http://www.medscape.com/viewarticle/512463 through http://www.medscape.com.
Stone, C. (2004 November 10, Updated). Autoimmune liver disease panel. Medline Plus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003328.htm.
Peng, S. (2005 April 20). Anti-smooth muscle antibody. Medline Plus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003531.htm.
(© 2005). Smooth Muscle Antibody, IgG with Reflex to Titer. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.arup-lab.com/guides/clt/tests/clt_203b.jsp#3219875 through http://www.arup-lab.com.
Strassburg, C. and Manns, M. (2003 January 9). Autoantibodies and Autoantigens in Autoimmune Hepatitis. Medscape from Semin Liver Dis 22(4): 339 -351, 2002 [On-line journal]. Available online at http://www.medscape.com/viewarticle/445619 through http://www.medscape.com.
Czaja, A. and Freese, D. et. al. (2002 August). Diagnosis and treatment of autoimmune hepatitis. National Guideline Clearinghouse [On-line information]. Available online through http://www.guideline.gov.
(© 2005). F-Actin (Smooth Muscle) IgG by Enzyme. ImmunoassayARUP's Guide to Clinical Laboratory Testing [[On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_a254.jsp#5444091 through http://www.aruplab.com.
(© 2003). Actin (Smooth Muscle) Antibody. LabCorp [On-line test information]. Available online at http://www.labcorp.com/datasets/labcorp/html/chapter/mono/se018700.htm through http://www.labcorp.com.