These autoantibody tests may be ordered along with other testing when a doctor is investigating liver disease and wants to distinguish between different causes of liver injury, including viral infections, drugs, alcohol abuse, toxins, genetic conditions, metabolic conditions, and autoimmune disorders.
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.
Titers of SMA may be lower in children and in those with compromised immune systems. The levels may vary over the course of the disease and are not closely related to the severity of autoimmune symptoms or to a person's prognosis.
The presence of SMA, F-actin antibodies, and ANA are highly suggestive of autoimmune hepatitis but not diagnostic. When significant concentrations of both are present and the doctor suspects autoimmune hepatitis, then a liver biopsy may be performed to look for characteristic signs of damage and scarring in the liver tissue.
This article was last reviewed on July 15, 2013. | This article was last modified on September 26, 2013.
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