Smooth Muscle Antibodies (SMA)

Smooth muscle antibodies (SMA) are autoantibodies, proteins produced by the body’s immune system that recognize and attack its own actin, a protein found in smooth muscle and other tissues, especially the liver. This test detects and measures the amount (titer) of SMA (or antibody against actin) in the blood.

For normal person the SMA is negative and the titer is <1:20(indirect immunofluorescence).The SMA positive rate of elderly person is about 5%.

A significant increase in the blood titer of SMA or actin antibody and/or ANA is usually due to autoimmune hepatitis type 1 or primary biliary cholangitis (PBC) in some cases.
A negative SMA or actin antibody test and an increased titer of LKM1 may indicate autoimmune hepatitis type 2.
If the SMA or actin antibody test and other antibody tests are negative, then symptoms and liver injury may be due to causes other than autoimmune hepatitis.

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.