The Anti-Smooth Muscle Antibody (ASMA) test is a blood test detecting autoantibodies that mistakenly attack smooth muscle cells, mainly in the liver, helping diagnose autoimmune hepatitis (AIH) and other autoimmune liver diseases like primary biliary cirrhosis, by showing the immune system’s attack on the body’s own tissues. Doctors use it with other tests (LFTs, biopsies) to confirm AIH, differentiate it from other liver issues (viral/alcohol-related), and monitor treatment, often requiring overnight fasting and avoiding alcohol before the blood draw