Performances of Clinical Disease Activity Index (CDAI) and Simplified Disease Activity Index (SDAI) appear to be better than the gold standard Disease Assessment Score (DAS-28-CRP) to assess rheumatoid arthritis patients

Background/Purpose To compare the performance of Disease Assessment Score of 28 joints - C-reactive protein (DAS-28-CRP), Clinical Disease Activity Index (CDAI) and Simplified Disease Activity Index (SDAI) composite measures to assess status of patients with rheumatoid arthritis (RA) on methotrexate, versus DAS-28 CRP as the gold standard. Methods One hundred and thirty-five patients with RA as per the 2010 American College of Rheumatology/European League Against Rheumatism criteria were included in the prospective study. The disease activity was assessed at baseline and at every 6 weeks for 24 weeks, by DAS-28-CRP, CDAI and SDAI. Patients were divided into groups of remission, low, moderate and high activity on the basis of predefined cut-offs for DAS-28-CRP, CDAI and SDAI. A Spearman correlation between composite measures and inter-group comparison of the measures was performed. Results There was an excellent positive correlation between DAS-28-CRP and CDAI (linear weighted kappa baseline - 0.545), DAS-28 CRP and SDAI (linear weighted kappa - 0.689) at baseline. There was moderate agreement between DAS-28-CRP and CDAI (linear weighted kappa final visit - 0.458) at final visit. There was moderate correlation between SDAI and DAS-28-CRP at final visit (linear weighted kappa - 0.470). However, correlation between CDAI versus SDAI remained excellent at baseline and final visit. Patients in remission as per DAS-28-CRP had significantly more residual disease activity compared to SDAI and CDAI remission criteria. Conclusion The study shows an excellent strong positive correlation between DAS-28-CRP, CDAI and SDAI at initial evaluation but not at final visit. SDAI- and CDAI-based remission criteria seem to be better than DAS-28-CRP-based remission criteria.