To evaluate whether the revised disease activity cut-off values for the Simplified Disease Activity Index (SDAI) and the Clinical Disease Activity Index (CDAI) are in congruence with the Disease Activity Score including a 28-joint count (DAS28) disease activity criteria in daily clinical routine.
A total of 570 rheumatoid arthritis (RA) outpatients were assessed and categorized according to the DAS28, the SDAI, and the CDAI. These results were compared to the respective DAS28 disease activity categories. Statistical evaluation was carried out by calculating alpha, the Spearman rank correlation, and kappa-statistics.
DAS28, SDAI, and CDAI levels were significantly correlated to one another on a group level (p < 0.001). Internal consistency was the highest for the CDAI (alpha = 0.783) and the lowest for the DAS28 (alpha = 0.664). Kappa-statistics revealed a substantial degree of agreement with respect to mild, moderate, and high disease activity according to the three scores, with exceptions concerning the definition of a remission-like state. Further categorization showed that an additional 44% of patients were found to be in remission according to the DAS28 disease activity criteria relative to those defined by the SDAI or the CDAI disease activity categories respectively.
The revised SDAI limits for disease activity and the respective CDAI thresholds proved to be in congruence with the DAS28 disease activity categories in daily clinical routine. The SDAI and the CDAI were found to be more stringent in defining remission.