To examine the validity, reliability, and predictive value of two recently developed composite disease activity measures, the Simplified Disease Activity Index (SDAI) and the Clinical Disease Activity Index (CDAI) in rheumatoid arthritis (RA) patients.
A systematic review of the published literature was performed between February 2003 and November 2007. Data was extracted regarding correlations of the SDAI and CDAI with standard clinical trial measures, the predictive ability of the measures and correlations with changes in radiographic scores. The ability of the measures to categorize patients according to their disease activity status compared to standard categories was also examined.
Among 17 studies initially identified, 12 provided information on the validity and reliability of the SDAI and CDAI. These measures were found to be strongly correlated with the Disease Activity Score (DAS28) with correlation coefficients ranging from 0.80 to 0.93. Areas under the curve (AUC), from receiver operating characteristic (ROC) curve analysis predicting physician responses, varied from 0.821 to 0.923. Moderate association with changes in the HAQ and radiographic scores was found with correlation coefficients ranging from 0.30 to 0.59. Several studies reported mixed results between the measures when categorizing patients according to disease severity with the SDAI and CDAI the more stringent at remission.
The SDAI and the CDAI were found to have concurrent validity and were highly predictive of a change in therapy, but not predictive of future functional capacity or joint damage. Differences were found when categorizing patients according to disease activity level. Further studies should be conducted, especially at remission and low disease activity status, before these measures are used independently in a clinical setting.