CRP and rheumatoid arthritis: However, CRP, ESR and calprotectin failed as a predictive factor in differentiating RA from OA patients (CRP: AUC = 0.565, 95%CI: 0.401–0.633; ESR: AUC = 0.543, 95%CI: 0.416–0.692; calprotectin: AUC = 0.570, 95%CI: 0.408–0.641) (Table 5).