Rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP)
RF is an autoantibody that reacts to the Fc portion of polyclonal IgG and other immunoglobulin classes (most assays detect the IgM rheumatoid factor). RF is helpful in evaluating patients who may have rheumatoid arthritis (RA), although it is absent in about 15% of patients with rheumatoid arthritis. RF-positive patients are more likely to have progressive, erosive arthritis with joint mobility loss and extraarticular manifestations, including rheumatoid nodules and vasculitis. On the other hand, RF can be present in other autoimmune disorders.
Another biomarker that is approximately 95% specific in diagnosing RA is the presence in serum of autoantibodies against cyclic citrullinated peptide (anti-CCP). Testing for both RF and anti-CCP may be beneficial when excluding the diagnosis of RA.
Antinuclear antibody (ANA)
Autoantibodies to nuclear antigens (ANAs) are a diverse group of antibodies that react against nuclear, nucleolar, or perinuclear antigens. These antigens represent cellular components such as nucleic acid, histone, chromatin, nuclear, and ribonuclear proteins. Testing for ANA is commonly performed to help diagnose many autoimmune connective tissue diseases.
The next section of this course will concentrate on the ANA test, including its methods, staining patterns, and interpretations.
