Comparison of the DAS28-CRP and DAS28-ESR in patients with rheumatoid arthritis

Aim To compare the Disease Activity Score with 28 joint (DAS28) using erythrocyte sedimentation rate (ESR) (DAS28‐ESR) and DAS28 using C‐reactive protein (CRP) (DAS28‐CRP) with thresholds validated for DAS28‐ESR in Turkish patients with rheumatoid arthritis. Method The DAS28 data of 112 patients with rheumatoid arthritis followed in a local outpatient clinic were used. First, the correlation between DAS28‐CRP and DAS28‐ESR and the correlation between their unique components ([0.36 × In (CRP + 1) + 0.96] and [0.70 × In (ESR)]) were analyzed. Second, a Bland–Altman plot was constructed for the evaluation of the level of agreement between DAS28‐CRP and DAS28‐ESR. Lastly, the agreement between these two methods was analyzed by κ coefficient. Results Although there was a strong correlation between DAS28‐CRP and DAS28‐ESR, the correlation between their unique components was fair. Although more than 95% of the point data fall between the upper and lower bounds of the limit of agreement, the percentage error (46%) was higher than the acceptable proportion of 30%. The κ coefficient of agreement between DAS28‐ ESR and DAS28‐CRP with validated thresholds for DAS28‐ESR was 0.42, which was close to the lower boundary for moderate agreement. Conclusion The results of this study demonstrated that there is discordance between DAS28‐ESR and DAS28‐CRP with the validated thresholds for DAS28‐ESR. Using the DAS28‐CRP with threshold values validated for DAS28‐ESR may lead to errors in the determination of disease activity and therefore may lead to errors in the management of patients with rheumatoid arthritis.