Prevalence and concentration of IgM rheumatoid factor in polyarticular onset disease as compared to systemic or pauciarticular onset disease in active juvenile rheumatoid arthritis as measured by ELISA.

The prevalence and concentration of IgM rheumatoid factor (RF) in children with juvenile rheumatoid arthritis (JRA) and its major disease onset groups remains uncertain. In our study enzyme linked immunoabsorbent assay (ELISA) of 68 children with active JRA showed IgM RF in the area of 67% (16/24) of those with polyarticular onset disease, 26% (7/27) of those with systemic onset disease, and 6% (1/17) of those with pauciarticular onset disease. The median IgM RF concentration was 50-fold higher in polyarticular disease compared to systemic disease. The prevalence of IgM RF in polyarticular disease was greater in those with severe disease (functional classes and 3 and 4), with 90% (9/10) seropositive. By agglutination assay, the prevalence of IgM RF in JRA was significantly less than by ELISA, with 33% of the polyarticular group positive for IgM RF, and none of the systemic group positive, Relatively low concentration IgM RF similar to that seen in systemic JRA was also found in high prevalence in the area of children with non-JRA, systemic rheumatic disease (n = 8). In summary, our study shows by ELISA that high concentrations of IgM RF are found essentially only in the sera of children with polyarticular onset JRA and especially in those with severe disease.