Evaluating disease activity in rheumatoid arthritis: which composite index is best? A systematic literature analysis of studies comparing the psychometric properties of the DAS, DAS28, SDAI and CDAI.

OBJECTIVES

To evaluate and compare four composite indices for assessing the activity of rheumatoid arthritis (RA).

METHODS

We conducted a systematic literature review by searching Medline via PubMed and Embase and Cochrane databases for articles published up to March 2009. We selected studies that directly compared at least two of the four composite indices. The DAS (Disease Activity Score), DAS28, Simplified Disease Activity Index (SDAI) and Clinical Disease Activity Index (CDAI) were evaluated in terms of reproducibility, construct validity, discriminative performance, and sensitivity to change.

RESULTS

We included 61 articles. The only study that directly compared the intraobserver reproducibility of the DAS28, SDAI, and CDAI found comparable intraclass correlation coefficients ranging from 0.85 to 0.89. Concordance among indices was good (kappa values of ∼0.7), except between the DAS28 and the other indices in definition of remission (kappa 0.48-0.63). The indices had good construct validity by their similar fair-to-good correlations with the Health Assessment Questionnaire (HAQ) score and structural damage. Discriminative performance was comparable and satisfactory for treatment changes or remission according to the American College of Rheumatology (ACR). Two studies evaluated the sensitivity to change of the SDAI and CDAI; both indices detected a difference between responders and non-responders according to ACR definitions.

CONCLUSION

The DAS, DAS28, SDAI, and CDAI are valid tools for evaluating the activity of RA. The DAS28 is less conservative in defining remission than are the other three indices. Longitudinal studies of individual patients are needed to confirm these results.