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Rheumatoid Factor

- Discussion:
    - RF is term used to describe group of autoantibodies w/ anti-IgG activity;
    - about 80-90% of RA pts have antibodies to the Fc region of IgG;
    - this antibody, called rheumatoid factor (anti-IgG), will also occur in bacterial endocarditis, schistosomiasis, leprosy, osteomyelitis, and other chronic infections;
           - it is also found in some patients with other connective tissue diseases;
    - although the presence of this antibody in the serum does not cause disease, there is evidence indicates that RF, locally produced w/ in joint, can form immune complexes & effect an inflammatory response;
           - can be considered amplifier of rheumatoid inflammation;
    - RF is a useful diagnostic test for rheumatoid arthritis, and the titers in RA are usually much higher than those in other inflammatory illnesses;
           - 80% of RA patients have rheumatoid factor in their blood;
    - high titers usually are diagnostic, but titers of 1:20 to 1:80 are in grey zone;
    - note that a negative RA titer with a positive clinical picture may indicated a seronegative arthritis;
    - diff dx:
           - in 5-10% of healthy persons older than 60 years, RF may be detected in a significant titer;
           - lupus;
           - mixed cryoglobulinemia (from hepatitis C or other infectious process);
                   - in this situation, steroids may worsen the viremia