Background: The purpose of this study was to examine whether levels of C-reactive protein (CRP), a sensitive marker of disease activity in rheumatoid arthritis (RA), are associated with increased risk of subsequent RA.
Methods: Eligible subjects were 39 876 healthy women from the Women's Health Study, a completed randomized trial of aspirin and vitamin E in cardiovascular disease and cancer prevention, begun in 1992. We included 27 939 women who provided blood samples at baseline that could be assayed for CRP.
Results: During 9.9 years of follow-up, 398 women reported a new diagnosis of RA. Of these, 90 cases were confirmed on medical chart review using American College of Rheumatology criteria. In age-adjusted analysis, the relative risks for developing confirmed, incident RA associated with increasing tertiles of CRP (first, second, and third) were 1.00 (reference value), 0.94 (0.54-1.61), and 1.29 (0.78-2.12) (P = .30 for trend). Further adjustment for randomized treatment, age, body mass index, and smoking demonstrated corresponding relative risks of 1.00 (reference value), 0.95 (0.55-1.65), and 1.33 (0.77-2.30) (P = .48 for trend). When we examined whether CRP levels predicted incident RA within 4 years, between 5 to 8 years, and 9 or more years after CRP measurement, we found no significant associations for any time period.
Conclusions: In this prospective study of healthy women, a single CRP level did not predict increased risk of RA. Furthermore, CRP measurement closer to the time of diagnosis was not predictive. The consistency of this effect throughout different time periods from diagnosis suggests that CRP does not have a large effect in predicting incident RA.