This test looks for smooth muscle antibodies (SMAs) in the blood. A smooth muscle antibody (SMA) is a type of antibody known as an autoantibody. Normally, the immune system makes antibodies to attack foreign substances like viruses and bacteria. An autoantibody attacks the bodys own cells and tissues by mistake. SMAs attack smooth muscle tissues in the liver and other parts of the body. An SMA test is primarily used to diagnose autoimmune hepatitis. It is also used to find out if the disorder is type 1 or type 2. SMA tests are also often used along with other tests to help confirm or rule out a diagnosis of autoimmune hepatitis.