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 patients 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.