Rheumatoid factor is the autoantibody most relevant in rheumatoid arthritis. Rheumatoid factor is characterized as an antibody against the fragment crystallizable portion of immunoglobulin G. When rheumatoid factor and immunoglobulin G join, immune complexes that contribute to the disease process are formed.
Patients suspected of having arthritis are evaluated for rheumatoid factor (RF). However, positive RF results may be attributed to other causes, such as tissue or organ rejection, and negative results do not rule out disease. RF is evaluated along with other signs and symptoms of arthritis and may be useful in diagnosis and outcome prediction.
RF is determined to be high or elevated when the level reaches more than 20 IU/mL, 1:40 or above the 95th percentile. However, different laboratories maintain different standards. High RF is part of the disease criteria of rheumatoid arthritis and may also be used in diagnosing Sjögren’s syndrome, Epstein-Barr virus or parvovirus infection.
RF may be linked to poorer disease outcomes, including persistently active synovitis, more joint damage and greater eventual disability.
Those with chronic hepatitis, primary biliary cirrhosis, any chronic viral infection, bacterial endocarditis, leukemia, dermatomyositis, infectious mononucleosis, systemic sclerosis and systemic lupus erythematosus may have elevated RF.
Any patient who may have arthritis can be measured for RF. Although seropositivity or seronegativity are not perfectly reliable predictors of rheumatoid disease, disease severity is often worse in those who are seropositive.
Results may be reported as titers or units. Although RF is not highly sensitive or specific as a screening tool for rheumatoid disease, it can be predictive in patients with symmetric polyarticular joint swelling.
Positive RF has significant associations with rheumatoid disease and Felty’s syndrome and insignificant associations with a host of conditions, ranging from systemic lupus erythematosus, mixed connective tissue disorder, syphilis, HIV, mononucleosis and a number of others.
Additional information about rheumatoid factor may be found at these websites: