Smooth muscle antibodies (ASMA)

The smooth muscle (SMA) or actin antibody test is primarily ordered along with antinuclear antibodies (ANA) and liver kidney microsomal type 1 (LKM-1) antibodies to help diagnose autoimmune hepatitis and to differentiate between the two major types of autoimmune hepatitis, type 1 and type 2.

A large increase in the blood titer of SMA or actin antibody is usually due to autoimmune hepatitis. A small increase in SMA or actin antibody may be present in up to 50% of patients with primary biliary cirrhosis (PBC). The SMA autoantibody may also be found in other conditions, such as infectious mononucleosis, hepatitis C, and some cancers.

If the SMA or actin antibody test is negative, then symptoms may be due to causes other than autoimmune hepatitis. However, most patients with autoimmune hepatitis who are negative for SMA or actin antibodies will be positive for ANA, LKM1, or other less frequently measured autoantibodies.

  • Sample of blood serum
  • We perform the test in 48 hours from sampling