Background The Disease Activity Score 28 (DAS 28-CRP/ESR) is widely used in the assessment of disease activity and response to treatment in patients with RA. The Simplified Disease Activity Index (SDAI) and Clinical Disease Activity Index (CDAI) are new tools for the evaluation of disease activity in Rheumatoid arthritis (RA). The scores impact on treatments options including the use of biological agents. The SDAI and CDAI are numerical sum calculators on five and four outcome parameters respectively: Swollen and tender joint assessment (using 28-joint count), patient and physician global assessment scores (VAS and PVAS (0 - 10) and the C-reactive protein (CRP) mg/dl (for the SDAI). Currently their use has been predominantly in trials rather than clinical practice.
Objectives Our hypothesis is that the CDAI and SDAI correlate very well with existing DAS28 assessment in patients with RA. We wanted to determine the correlation and agreement for remission and high disease activity between these scores. We attempted to establish whether these new scoring tools could be used as possible alternatives in clinical practice.
Methods We conducted a prospective study of 162 patients in rheumatology outpatients over a three month period. Disease activity was determined for each patient using all scoring tools - CDAI, SDAI, DAS28-ESR and DAS28-CRP. The proportion of patients within four categories (remission/low/moderate/high) were calculated for each scoring tool. Pearson correlation coefficients and 95% confidence intervals were calculated for each of the measures, along with contingency tables and Bland-Altman plots for agreements between scoring systems with kappa statistics.
Results Female patients accounted for 75.9% (n=123) and male patients for 24.1% (n=39). The mean age of the sample group was 62.1 (range 22 to 86). CDAI and SDAI correlate extremely well (pearson = 0.99, p<0.01). DAS28-CRP is strongly correlated with SDAI (pearson = 0.957, p<0.01) and CDAI (pearson = 0.948, p<0.01), while DAS28-ESR is less so: SDAI (pearson = 0.921, p<0.01) and CDAI (pearson = 0.914, p<0.01). DAS28-CRP shows moderate agreement with SDAI and CDAI (Kappa = 0.51 and 0.48), and DAS28-ESR also shows moderate agreement (SDAI Kappa = 0.56; CDAI Kappa = 0.54). Some tools consistently scores higher than others. The extreme end of the scales is where most of the outliers occur on comparison of the tools.
Conclusions Using all four tools in combination is time consuming. DAS28-CRP correlates better with the SDAI/CDAI modalities than DAS28-ESR. The absolute agreement/kappa values between each system indicate their use is not interchangeable, therefore, one scoring tool should be used for consistency. Although there is a strong correlation between DAS28-CRP and DAS28-ESR, patients consistently score higher on the ESR measure - which may reflect the age demographic. Despite good correlation overall, the greatest mismatch between scores seems to be in remission and low disease activity categories. However, in high disease activity there is strong correlation between the scores and as such in patients with severe active disease CDAI/SDAI may be plausible alternatives.
The Simplified Disease Activity Index (SDAI) and the Clinical Disease Activity Index (CDAI): a review of their usefulness and validity in rheumatoid arthritis. Aletaha D, Smolen J. Clin Exp Rheumatol. 2005 Sep-Oct;23(5 Suppl 39):S100-8.
Acknowledgements Rheumatology; Research & Development Departments - East Sussex Healthcare NHS Trust
Disclosure of Interest None declared