Anti-smooth muscle antibody
Anti-smooth muscle antibody is a blood test that detects the presence of antibodies against smooth muscle. The antibody is useful in making a diagnosis of autoimmune hepatitis.
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.
The 3 types of muscle tissue are cardiac, smooth, and skeletal. Cardiac muscle cells are located in the walls of the heart, appear striated, and are under involuntary control. Smooth muscle fibers are located in walls of hollow visceral organs, except the heart, appear spindle-shaped, and are also under involuntary control. Skeletal muscle fibers occur in muscles which are attached to the skeleton. They are striated in appearance and are under voluntary control.
How the Test is Performed
A blood sample is needed. This may be taken through a vein. The procedure is called a venipuncture.
How to Prepare for the Test
No special steps are needed to prepare for this test.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others may feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
You may need this test if you have signs of certain liver diseases, such as hepatitis and cirrhosis. These conditions can trigger the body to form antibodies against smooth muscle.
Anti-smooth muscle antibodies are not often seen in diseases other than autoimmune hepatitis. Therefore, it is helpful to make the diagnosis. Autoimmune hepatitis is treated with immunosuppressive medicines. People with autoimmune hepatitis often have other autoantibodies. These include:
- Antinuclear antibodies.
- Anti-actin antibodies.
- Anti-soluble liver antigen/liver pancreas (anti-SLA/LP) antibodies.
- Other antibodies may be present, even when the anti-smooth muscle antibodies are absent.
The diagnosis and management of autoimmune hepatitis may require a liver biopsy.
Normal Results
Normally, there are no antibodies present.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
A positive test may be due to:
- Chronic active autoimmune hepatitis
- Cirrhosis
- Infectious mononucleosis
The test also helps distinguish autoimmune hepatitis from systemic lupus erythematosus.
Risks
Risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
References
Czaja AJ. Autoimmune hepatitis. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 90.
Ferri FF. Laboratory values and interpretation of results. In: Ferri FF, ed. Ferri's Best Test: A Practical Guide to Clinical Laboratory Medicine and Diagnostic Imaging. 5th ed. Philadelphia, PA: Elsevier; 2023:139-252.
Tanaka A. Autoimmune Hepatitis: 2019 Update. Gut Liver. 2020;14(4):430-438. doi: 10.5009/gnl19261. PMID: 32301319; PMCID: PMC7366136.
Williams MJ, Gordon-Walker TT. Hepatology. In: Penman ID, Ralston SH, Strachan MWJ, Hobson RP, eds. Davidson's Principles and Practice of Medicine. 24th ed. Philadelphia, PA: Elsevier; 2023:chap 24.
Version Info
Last reviewed on: 1/25/2023
Reviewed by: Neil J. Gonter, MD, Assistant Professor of Medicine, Columbia University, NY and private practice specializing in Rheumatology at Rheumatology Associates of North Jersey, Teaneck, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
