A new method for the detection of hidden IgM rheumatoid factor in patients with juvenile rheumatoid arthritis.

The sera of 56 children with active seronegative juvenile rheumatoid arthritis were examined for the presence of hidden IgM rheumatoid factors (RF) by use of a rapid new method consisting of ion exchange chromatography and an ELISA assay. Elevated hidden IgM-RF levels were detected in 57% of all patients (median value 0.6 IU/ml, p less than 0.01), in 67% of patients with polyarticular disease (1.1 IU/ml, p less than 0.005), in 62% of the group with monoarticular disease (0.6 IU/ml, p less than 0.02), and in 60% of the group with systemic disease (0.6 IU/ml, NS). Whereas hidden IgM-RF plays no role in HLA-B27 positive disease, we found raised titers in 86% of B27 negative patients (0.8 IU/ml, p less than 0.001).