Comparison of Activity Score DAS28-ESR and DAS28-CRP in Moroccan Patients with Rheumatoid Arthritis

Background: Disease Activity Score-28 joints (DAS-28) is nowadays the gold standard for measuring the disease activity in patients with RA. The original DAS-28 was based on erythrocyte sedimentation (ESR), but an alternative formula incorporating C-reative protein (CRP) [DAS-28(CRP)] has been developed. Objectives: To compare the disease activity score DAS28-ESR versus DAS28–CRP, and to determine the factors that might influence their difference. To estimate the disease activity score DAS28-CRP threshold values that correspond to DAS28ESR values in Moroccan patients with rheumatoid arthritis. Patients and methods: Patients with RA were included in a cross-sectional study. We have collected the demographic characteristics and the characteristics of the RA: duration of evolution, global disease activity on a 100 mm visual analogue scale assessed both by the patient (GDAP), morning stiffness in minutes, functional impact of the disease assessed by the HAQ (Health Assessment Questionnaire), and current corticosteroid dose. The disease activity was assessed by the DAS28-ESR and DAS28-CRP. A concordance correlation between DAS28-ESR and DAS28 -CRP was performed. We defined a new variable DIFDAS=DAS28-ESR – DAS28-CRP (differences between the two indexes). Factors influencing this difference were tested by univariate then multivariate logistic regression. Using DAS28-ESR as gold standard, the passing Bablok and BlandAltman methods were used to assess the agreement between DAS28-ESR and DAS28-CRP. Results: 103 patients were included with a female predominance (87.4 %). Mean age was 49.7 ± 11.4 years. Median disease duration was 8 years [3-14]. There was a strong positive concordance between the two indexes of 0.93 with CI 95% [0.91-0.95], although the DAS28-ESR value obtained was higher than that of DAS28-CRP at approximately 90% of the visits (n= 93). Significantly, the difference between both indexes was higher than 0.6 in 42.7% of the visits studied (n=44). In multivariate analysis, factors significantly associated with this difference were high dose of steroids and significant functional impairment (p< 0.05). There was a difference between DAS28-ESR and DAS28-CRP values (p< 0.05). Using bland and Altman method, we found that DAS28CRP under-estimate threshold values of DAS28-ESR by 0.49 with CI 95% [-1.96, +1.96]. Conclusion: Our study showed a positive concordance between the DAS28-ESR and DAS28 -CRP. But DAS28-ESR would be higher than DAS28-CRP in patients with high dose of corticosteroids and significant functional impairment.