Original articleEvaluating 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
Introduction
Rheumatoid arthritis (RA) is an inflammatory joint disease that causes structural joint damage, incapacitation, and alterations in quality of life. These adverse consequences can be prevented, at least in part, by early appropriate therapy, in particular a “tight control” strategy [1]. Such strategy necessitates evaluating disease activity and response to treatment with objective and standardized tools. In contrast to other diseases such as hypertension and diabetes, the activity of RA cannot be evaluated by a single clinical or laboratory measurement. Therefore, in the 1990s, composite indices based on several clinical and/or laboratory variables were developed. These indices reduce measurement error, allow for objective evaluation of patients seen in everyday practice, and benefit the analysis and interpretation of clinical trials of new, potential disease-modifying drugs.
The first composite index developed for assessing disease activity in RA patients was the Disease Activity Score (DAS or DAS44) [2]. Then, another group developed a simplified version based on 28 joints instead of 44, the DAS28, which is currently the most widely used index [3]. However, the DAS44 and DAS28 are based on complex equations, and their determination requires a dedicated software program or calculator. This drawback led to the development of simpler indices, the Simplified Disease Activity Index (SDAI) [4] and its modified version, the Clinical Disease Activity Index (CDAI) [5].
Which index to use in clinical practice or in clinical research is difficult to determine. One way to compare the indices is to compare their psychometric properties, as defined by the OMERACT filter [6]. The OMERACT filter checks that a potential outcome measure is truthful (reflects what it is supposed to reflect), reliable (reproducible), and discriminant (sensitive to change, over time, and between different severity stages). The composite indices cited above have met the filter requirements. However, for true evaluation, they should be compared with each other.
Thus, the aim of this study was to perform a systematic literature review of studies comparing the DAS, DAS28, SDAI and CDAI in terms of reproducibility, concordance, construct validity, discriminative performance, and sensitivity to change.
Section snippets
Methods
We conducted a systematic literature review by searching Medline via PubMed and the Embase and Cochrane databases for articles published in English or French up to March 2009, without date limits, using the following terms: (DAS [ti] OR SDAI [ti] OR CDAI [ti] OR disease activity score [ti] OR disease activity index [ti]) AND arthritis, rheumatoid [MeSH]. We also searched meeting abstracts of the American College of Rheumatology (ACR), European League Against Rheumatism, and French Society of
Data collection
One investigator (CGV) selected the articles and collected the data using a predetermined form. The following data were collected: type of study, number of patients, and rheumatoid arthritis features.
The outcomes were reproducibility (interobserver, intraobserver), concordance, construct validity, discriminative performance, and sensitivity to change (after an effective therapy).
Reproducibility
Interobserver and intraobserver reliability was estimated by calculating intraclass correlation coefficients (ICCs), unweighted kappa statistics, and overall agreement (defined as the percentage of observed exact agreements).
Concordance
Concordance was the ability of the different indices to classify patients in the same activity grades or in the same response to treatment grades.
Construct validity
Construct validity was achieved when measures agreed with other measures that evaluate the same phenomenon. We compared the
Article selection
Our systematic literature search identified 102 articles, of which 50 were excluded on the basis of their titles and abstracts. Finally, 61 articles were included (Fig. 1). Among them, 17 articles met the inclusion criteria and were analyzed.
DAS
The DAS44 was developed in 1990 in a prospective study of up to three years’ duration of 113 patients with early RA (duration less than one year) [2]. The disease was considered active if a disease-modifying antirheumatic drug (DMARD) was started or stopped
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
Acknowledgement statement
This work was supported by an unrestricted educational grant from Abbott France.
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