Clinical correlations with serum C1q levels in patients with rheumatoid arthritis.

Previous studies have suggested that serum C1q levels measured during the first 5 years of rheumatoid arthritis (RA) may be predictive of the extent of subsequent joint damage. To further evaluate the clinical significance of this marker in RA, levels of C1q were measured by radial immunodiffusion in serum samples from 107 well-characterized patients with RA. Mean levels of C1q were higher in patients with a disease duration less than or equal to 5 years (173 micrograms/ml) than in patients with a disease duration greater than 5 years (148 micrograms/ml) (P = 0.032). Serum C1q levels were correlated with total joint counts and activities of daily living scores, but no correlation was observed with erythrocyte sedimentation rates or with radiographic scores. The results suggest that C1q may be a useful early marker of disease activity in patients with RA.