High prevalence of iga rheumatoid factor in severe polyarticular‐onset juvenile rheumatoid arthritis, but not in systemic‐onset or pauciarticular‐onset disease

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Abstract
The presence of IgA rheumatoid factor (IgA‐RF) has been correlated with severe joint disease in adult rheumatoid arthritis (RA), but IgA‐RF has not been reported in juvenile rheumatoid arthritis (JRA). In the present study, IgA‐RF was assayed by an enzyme‐linked immunosorbent assay and was found in the sera of 14 of 24 children (58%) with active polyarticular JRA. The presence of IgA‐RF correlated with the degree of functional disability. In contrast, IgA‐RF was not found in the sera of systemic‐onset disease patients, regardless of the degree of dysfunction. IgA‐RF was detected in only 1 patient with pauciarticular disease, despite the fact that several patients in this group had severe disease. The presence of IgA‐RF in polyarticular JRA did not correlate with serum IgA levels, but did correlate with the presence and the level of serum IgM‐RF. Thus, the presence of IgA‐RF appears to be specific for polyarticular JRA, and shows a correlation with severe disease in this group.