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 9 In (CRP + 1) + 0.96] and [0.70 9 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 j 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 j 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.

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