The association between C-reactive protein and the likelihood of progression to joint replacement in people with rheumatoid arthritis: a retrospective observational study.

Background: This study sought to evaluate the association between systemic inflammation as measured by C-reactive protein and total joint replacement and the association between change in CRP status (low, < or = 10 mg/L and high, >10 mg/L) measured over one year and total joint replacement in patients diagnosed with rheumatoid arthritis.

Methods: A cohort of patients was selected from The Health Improvement Network (THIN) dataset of anonymised patient-level data from UK general practice with a confirmed chronic rheumatic diagnosis. Surgery-free survival was evaluated using Cox proportional hazards regression models (CPHM).

Results: 2,421 cases had at least one CRP measurement of which 125 cases (5.2%) had at least one major joint replacement. In CPHM, each additional unit increase in log mean CRP (range 1 to 6) was associated with a hazard ratio (HR) for major orthopaedic surgery of 1.36 (95% CI 1.10 to 1.67; p = 0.004), after controlling for age at first rheumatoid presentation and average body mass index over the same observation period. Repeated CRP observations around one year apart were recorded in 1,314 subjects. After controlling for confounding factors, in cases whose CRP remained high (>10 mg/L), the HR for joint replacement increased more than two-fold (p = 0.040) relative to cases whose CRP remained low. In patients whose CRP increased from low to high, the HR was 1.86 compared to those who remained in a low state (p = 0.217). By comparison, among those subjects whose CRP was reduced from a high to low state, the hazard ratio was more than halved (1.46) from to those who remained high (p = 0.441). Although underpowered, the trend evident from CRP change corroborates the association of TJR progression with mean CRP.

Conclusion: CRP level predicts progression to major joint replacement after standardisation for relevant risk factors as did change in CRP status between low and high states observed over one year.