A rather non-specific test. Anti-smooth muscle antibodies are present in up to 70% patients with autoimmune chronic active hepatitis and in 25-40% of patients with primary biliary cirrhosis (often together with anti-mitochondrial antibodies).
Sera from patients with Type 1 chronic active hepatitis contain antibodies to smooth muscle antigens that are detectable by indirect immunofluorescence on the smooth muscle of several organs. The antibodies belong mainly to the IgG class, but can be IgM.
Low titres of anti-smooth muscle antibodies are also associated with infectious diseases giving hypogammaglobulinaemia. Lower levels (usually) are also found in connective tissue diseases and chronic infections. The antigen recognised by anti-smooth muscle antibodies in sera of patients with Type 1 chronic active hepatitis is often reported to be actin.
A rather non-specific test for autoimmune liver disease particularly autoimmne hepatitis but also positive in connective tissue diseases and in chronic infections.
Smooth muscle antibodies are detected in:
- 40-70% of patients with Type 1 chronic active hepatitis
- 50% of patients with active hepatitis/primary biliary cirrhosis overlap.
- 28% of patients with cryptogenic cirrhosis
Type 1 chronic active hepatitis is often associated with hypergammaglobulinaemia and with anti-nuclear antibodies.
Anti-smooth muscle antibodies are also found in patients with acute viral hepatitis, infectious mononucleosis, asthma, yellow fever and malignant tumours (carcinomas of the ovary, malignant melanoma). They have been found in less than 2% of the normal population.
Antibody titres are in the range of 160 to 320 in Type 1 chronic active hepatitis but are often lower, in the other conditions listed above. They can be found in patients with rheumatoid arthritis, multiple sclerosis but probably not SLE.
Indirect immunfluorescence mouse tissue (liver kidney stomach).
Assay range notes
Positive samples Titre range 1:40-1:640
5 – 7 days