IGM RHEUMATOID-FACTOR ESTIMATION BY ELISA IN SERONEGATIVE RHEUMATOID-ARTHRITIS BEFORE AND AFTER IGM FRACTIONATION - DOES SERONEGATIVE RA EXIST

We looked for the presence of IgM rheumatoid factor (RF) using an enzy me-linked immunosorbent assay (ELISA) in 25 patients with active seron egative rheumatoid arthritis. In unfractionated sera, 12 patients (48% ) were positive for IgM RF (classical), but after IgM fractionation of 23 samples (2 samples were not available) using high performance liqu id chromatography for fractionating IgM, 12 patients were positive for RF by ELISA indicating the presence of hidden RE Finally, three patie nts were labelled as truly seronegative for IgM RF. Classical IgM RF a s deteced by ELISA correlated significantly with erosive disease. Hidd en RF did not correlate with disease activity or severity in this cros s-sectional study, and though its presence was associated with shorter disease duration, this did not reach statistical significance.