BOSTON, Massachusetts—C-reactive protein (CRP), a sensitive marker of systemic inflammation, is elevated in patients with rheumatoid arthritis (RA), but high CRP levels in otherwise healthy women do not predict subsequent development of RA, according to researchers from the Women's Health Study.

"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." —Nancy A. Shadick, MD.
Lead author Nancy A. Shadick, MD, reports in the Archives of Internal Medicine that CRP levels did not predict RA risk either using baseline CRP measured at study entry or using CRP measurements closer to the time of diagnosis.1 "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," she writes. Dr. Shadick is in the division of rheumatology, immunology, and allergy at Brigham and Women's Hospital, Harvard Medical School, in Boston, Massachusetts.

30,000 Women, Nearly 10 Years of Follow-Up

The Women's Health Study, a recently completed, prospective, randomized trial of aspirin and vitamins for the primary prevention of cardiovascular disease (CVD) and cancer, enrolled 39,876 women health professionals throughout the US who were 45 years or older and had no previous history of CVD, cerebrovascular disease, or cancer. Various other medical conditions (including RA) were documented in the baseline questionnaire, every 6 months during the first year of study, and yearly thereafter. Follow-up was 9.9 years.

This analysis included data for 27,213 women, of whom 398 reported a diagnosis of new onset RA during the follow-up period. Of these 398 self-reported cases, 97 were confirmed using the Connective Tissue Disease Screening Questionnaire (CSQ), with 90 of that group classified as "confirmed RA" based on medical record reviews.

The relative risks for developing confirmed, incident RA were 1.00 for the lowest tertile of CRP (0.03–1.11 mg/dL), 0.94 for the second tertile (1.12–3.27 mg/dL), and 1.29 for the highest tertile (3.28–174.9 mg/dL, P = .30 for trend). Adjusting for possible confounders such as randomized treatment, age, body mass index, and smoking did not change this relationship.

"We found...that a single measurement of CRP in individuals did not significantly predict subsequent risk of RA in women. C-reactive protein, instead, may be more of a marker of symptomatic disease rather than reflect a genetically or environmentally susceptible group," the authors conclude.

Reference

1. Shadick NA, Cook NR, Karlson EW, et al. C-reactive protein in the prediction of rheumatoid arthritis in women. Arch Intern Med. 2006;166:2490–2494.