Clinical relevance of IgA rheumatoid factor (RF) in children with juvenile rheumatoid arthritis.

This study proposed to investigate the prevalence and clinical relevance of serum immunoglobulin A (IgA) rheumatoid factor (RF) in juvenile rheumatoid arthritis (JRA) as published reports vary in their conclusion. Sera of 82 children with JRA and 25-age and sex-matched healthy children were measured for IgA RF by an enzyme linked immunoassay using human IgG as the antigen. Forty-three percent of the disease population were positive and the prevalence in pauciarticular, polyarticular and systemic onset was 9/18 (50%), 21/47 (44.7%) and 5/17 (27.7%) respectively when mean + 2SD of normal was taken as the cut-off value. By defining the upper limit of normal as mean + 6SD, 16/47 (34%) were positive in the polyarticular as compared to 2/18 (11.1%) in pauciarticular and 1/17 (5.8%) of systemic onset disease groups. The prevalence in the polyarticular subset with the upper cut-off limit was significantly higher than the pauciarticular and the systemic onset group (P < 0.05). Furthermore, the mean level of IgA RF was significantly higher in the polyarticular group compared to the mean level in the systemic onset group (P < 0.05). The mean level of IgA RF was also significantly higher (P < 0.05) in 61 children with active diseases.