The Anti-Nuclear Antibody (ANA) test measures the presence of antibodies that target the nuclei of cells. These antibodies are often found in individuals with autoimmune diseases, especially systemic lupus erythematosus (SLE), rheumatoid arthritis, and other connective tissue disorders. A positive ANA test can indicate an autoimmune condition, but it is not specific to one disease. The test is commonly used to help diagnose autoimmune disorders, assess disease activity, and monitor treatment responses. A blood sample is required for this test.