Rheumatoid factors are antibodies that attach to other antibodies. This may be associated with inflammation. It is a test used to help in the diagnosis of rheumatoid arthritis. However, there are many other conditions associated with a positive rheumatoid factor. These conditions include Sjogren's syndrome, viral illnesses (including hepatitis), tuberculosis, endocarditis, malignancy, and other inflammatory illnesses.
It is not uncommon for rheumatoid factor to be detected in healthy individuals. Approximately 1% to 2% of healthy people have detectable serum rheumatoid factor. And 10 to 20 % of rheumatoid arthritis patients are NOT rheumatoid factor positive. Those rheumatoid arthritis patients who are rheumatoid factor positive are at greater risk for more aggressive disease, including inflammation outside the joints---such as rheumatoid lung or inflammation of the eye. Patients with a positive rheumatoid factor are also more prone to have rheumatoid nodules---those "lumps" most often seen near the elbow.
Rheumatoid factor should not be used as a screening test (as, for example, the mammogram is used for screening for breast cancer) in healthy people because there are no therapies to prevent the development of rheumatoid arthritis. More importantly, the presence of rheumatoid factor in a healthy person does not mean that person will ever develop rheumatoid arthritis.
Another antibody, the anti-cyclic citrullinated peptide (CCP) antibody is another marker that might help physicians diagnose rheumatoid arthritis. A recent review of studies of the anti-CCP antibody showed that 3 of 4 studies found that the risk for bony destruction as seen on x-ray was greater in those patients with the CCP antibody compared to those patients who were only positive for rheumatoid factor. The study concluded that anti-CCP antibodies are more specific than rheumatoid factor for diagnosing rheumatoid arthritis and may better predict joint destruction.
It should not be forgotten that rheumatoid arthritis is a clinical diagnosis. A positive rheumatoid factor or anti-CCP antibody does not guarantee a diagnosis of rheumatoid arthritis (the CCP antibody has been found to be positive in other illnesses, including psoriatic arthritis, systemic lupus erythematosus and Sjogren's syndrome).
The American College of Rheumatology has established criteria for the classification of rheumatoid arthritis. These include the following:
- Morning stiffness lasting at least one hour.
- Arthritis of three or more joint areas.
- Arthritis of hand joints.
- Symmetric arthritis.
- Rheumatoid nodules.
- Serum rheumatoid factor.
- Radiographic changes.
For classification purposes, a patient shall be said to have rheumatoid arthritis if he/she has satisfied at least four of these seven criteria. Criteria 1 through 4 must be present for at leas 6 weeks.
As one can see, the rheumatoid factor is only one small part of the approach toward classifying a patient as having rheumatoid arthritis.