Comparative Measurement of Rheumatoid Factor in Serum and Synovial Fluid of Rheumatoid Arthritis Patients by ELISA and Latex-Agglutination

Rheumatoid factors (RF) are autoantibodies with specificity for the Fc portion of human IgG. Production of RF is a characteristic feature of rheumatoid arthritis (RA) and is detectable in high titer in about 90% of these patients. In this study, we measured total IgM, IgA, IgMRF and IgARF in serum and synovial fluid of 45 RA patients by ELISA and the results were compared with those obtained by latex agglutination test (LAT). The results show that from 45 RA patients, 93% (43:45) and 78% (35:45) were seropositive in ELISA and LAT, respectively. The sensitivity limit of LAT was approximately 10 µg/ml, whereas less than 10 ng/ml of RF was detectable by ELISA. There was a highly significant correlation between the concentration of IgMRF and latex agglutination titer in both serum (r = 0.78, p