Circulating immune complexes and rheumatoid arthritis: a comparison of different assay methods and their early predictive value for disease activity and outcome.

The performance of four different assays for circulating immune complexes-the C1q solid phase method, one using protein A and one using anti-IgG, C1q PEG, and the 2% PEG method-were compared in 61 patients with early rheumatoid arthritis followed up for two years. There were weak but statistically significant correlations between the results from some of the pairs of assays, but the changes over time from any single assay did not correlate with those from any of the other assays. None of the assays predicted either future disease activity, as measured by subsequent ESR, CRP, and articular index; or functional outcome, as measured by wrist extension, Steinbocker functional capacity, and the Stanford health assessment questionnaire. It is unlikely therefore that the measurement of immune complexes is of value in predicting early outcome in patients with rheumatoid arthritis.