Autoantibody tests are performed, along with x-rays and other imaging scans and biopsies, to help diagnose an autoimmune disorder. In some cases, they can also be used to help evaluate the severity of the condition, monitor activity of the disease, and assess the effectiveness of treatments.
Autoantibody tests may be requested when a person presents with chronic, progressive arthritic symptoms, fever, fatigue, muscle weakness, and/or a rash that cannot readily be explained. One of the most commonly requested tests is the antinuclear antibody (ANA) test. ANA is positive in a variety of autoimmune diseases, including systemic lupus erythematosus (SLE), Sjögren syndrome, rheumatoid arthritis, and autoimmune hepatitis. In patients with a positive ANA, a follow on test investigating a panel of 6 or more more specific autoantibody tests called extractable nuclear antigens (ENA) is typically requested. The particular ENA autoantibodies detected can help the doctor to determine if a particular autoimmune disorder is likely to be present.
Specific autoantibodies are usually present in a percentage of people with a particular autoimmune disorder. For instance, up to 80% of those with SLE will have a positive anti-double stranded DNA (anti-dsDNA) test, but only about 25-30% with SLE will have a positive anti-ribonucleoprotein (anti-RNP). Some individuals with an autoimmune disorder will have negative autoantibody test results but, at a later date as the disorder progresses, autoantibodies may develop. A small percentage of the general population may have one or more autoantibodies present in their blood with no associated symptoms. Autoantibodies are also more commonly found in older people.