Anti-smooth muscle antibody

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Definition

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.

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 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
  • Antiactin antibodies
  • Anti-soluble liver antigen/liver pancreas (anti-SLA/LP) antibodies
  • Others

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:

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)

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Blood testTypes of muscle tissue

References

Chernecky CC, Berger BJ. Anti-smooth muscle antibody - serum. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:155.

Czaja AJ. Autoimmune hepatitis. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 90.

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