Autoantibodies

Why are autoantibody tests done?

Autoantibody tests are used to help diagnose autoimmune disorders. In a few cases, they are used to help evaluate the severity of the condition, monitor remissions, flares and relapses of the disorder and to monitor the effectiveness of treatments.

Autoantibody tests may be ordered when a patient presents with chronic, progressive arthritic symptoms, fever, fatigue, muscle weakness, and/or a rash that can not readily be explained. One test initially ordered is the Antinuclear antibody (ANA) test, a marker of the autoimmune process that is positive with a variety of autoimmune diseases. It may be positive in systemic lupus erythematosus, Sjögren’s syndrome, rheumatoid arthritis, autoimmune hepatitis, primary biliary cirrhosis, alcohol-related liver disease, and hepatitis B. It is frequently followed up with other specific autoantibody tests, such as anti-Double Strand DNA (anti-dsDNA), anti-Sjögren’s Syndrome A (anti-SS-A) (Ro), anti-Sjögren’s Syndrome B (anti-SS-B) (La) and Anti-Ribonucleic Protein (anti-RNP). In addition, other tests associated with arthritis and inflammation, such as an rheumatoid factor (RF), an erythrocyte sedimentation rate (ESR), a C-Reactive Protein (CRP), and/or complement levels (C3, C4), may also be performed.

A single autoantibody test is not diagnostic, but it adds weight to the doctor’s determination as to whether a particular autoimmune disorder is likely or unlikely to be present. Each autoantibody result should be considered individually and as part of the group. Some systemic disorders, such as Systemic Lupus Erythematosus (SLE) may be more likely if several autoantibodies are present, while others, such as Mixed Connective Tissue Disease (MCTD) may be more likely if a single autoantibody (anti-RNP - ribonucleic protein) is the only one present. Those who have more than one autoimmune disorder may have several detectable autoantibodies.

Whether a particular autoantibody will be present is both very individual and a matter of statistics. Each will be present in a certain percentage of people who have a particular autoimmune disorder. For instance, up to 80% of those with SLE will have a positive anti-double strand DNA (anti-dsDNA) test, but only about 25-30% will have a positive anti-RNP. Some individuals who do have an autoimmune disorder will have negative autoantibody test results, but at a later date – as the disorder progresses - the 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 more commonly found in older people.