Circulating immune complexes in patients with rheumatoid arthritis: correlation with disease activity.

Circulating immune complexes (CIC) have been detected in the majority of patients with rheumatoid arthritis (RA). Their usefulness in monitoring disease activity is still controversial. Thirty-five patients with RA have been studied for the presence of CIC by the C1q binding assay. Abnormally high levels of CIC were detected in 83% of the patients and in 76% of 46 serum samples. Mean C1q binding activity for all serum samples was 27.4 +/- 25 compared to 7.5 /+- 2% in a control group of healthy individuals. A highly significant correlation was observed between C1q binding activity and the following indices of disease activity: the erythrocyte sedimentation rate, the latex and Rose-Waaler tests and a systemic index. The level of CIC in RA patients seems to be a reliable index of disease activity.