Anti–Smooth Muscle Antibodies (ASM)

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Subject: Anti–Smooth Muscle Antibodies (ASM)

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Definition

  • Smooth muscle antibodies are directed toward actin, myosin, and occasionally against other contractile proteins in muscle cells. Smooth muscle antibodies can present in a variety of liver disease states. Smooth muscle antibodies can be useful in differentiating liver disease when used in conjunction with other laboratory results and the patient's clinical symptoms.

  • Normal range:

    • IFA: negative; if positive, results are tittered, ELISA: <1:40 titer.

    • ASM titers >1:40 are significant.

Use

  • Aids in the diagnosis of chronic active hepatitis

  • Differential diagnosis of liver disease

  • Rule out SLE (test usually negative in SLE)

Interpretation

Increased In

  • Chronic active hepatitis

  • Autoimmune hepatitis type 1

  • Hepatitis B

  • Hepatitis C

  • Primary biliary cirrhosis

  • Primary sclerosing cholangitis

  • Overlap syndromes

Decreased In

  • NA

Limitations

  • A positive test is not diagnostic for any one disease state.

  • Low titers are seen in acute viral hepatitis, PBC, infection mononucleosis, malignant myeloma, and ovarian carcinoma.

 
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