Reliability and validity of CDAI and SDAI indices in comparison to DAS-28 index in Moroccan patients with rheumatoid arthritis

BACKGROUND Clinical disease activity index (CDAI) and simplified disease activity index (SDAI) are useful tools for the evaluation of disease activity in patients with rheumatoid arthritis (RA), but have not been comparatively validated in Moroccan population. Therefore, this study was designed to assess validity and reliability of CDAI and SDAI in comparison to disease activity score-28 joints (DAS-28) in Moroccan patients with RA. METHODS Patients with RA were included in a cross-sectional study. Patient characteristics and RA were collected. The disease activity was assessed by DAS-28, CDAI and SDAI. Patients were splitted into groups of remission, low, moderate and high activity on the basis of predefined cut-offs for DAS-28, CDAI, and SDAI. A Spearman correlation between composite indexes and inter-group comparison of the indexes were performed. Using DAS-28 as a gold standard, the Receiver operator characteristic (ROC) curve was used to assess the performance of a screening test at different levels. RESULTS The study was conducted with 103 patients of female predominance (87.4%). Mean age was 49.7 ± 11.4 years. Median disease duration was in the order of 8 years [3-14]. There was an excellent correlation between DAS-28 and CDAI (r = 0.95, p <0.001), CDAI and SDAI (r = 0.90, p <0.001), and DAS-28 and SDAI (r = 0.92, p <0.001). There was a good inter-rater alignment between the DAS-28 and CDAI (Weighted kappa =0.743) and there was a moderate inter-rater alignment between the DAS-28 and SDAI (Weighted kappa =0.60), and also between the SDAI and CDAI (Weighted kappa = 0.589). There was no statistically significant difference between AUROC of CDAI and SDAI as both were performed equally well. DISCUSSION This study is the first Moroccan case study to compare the performance of both CDAI and SDAI in evaluation of disease activity in patients with RA. Our study showed that there was a direct and excellent correlation between DAS-28 and CDAI, and SDAI and DAS-28. CONCLUSION Our study shows a strong positive correlation between DAS-28, CDAI and SDAI. The cut-off values for CDAI and SDAI used in western literature can be used with minor modifications in Moroccan scenario.