Objectives To derive and validate a new disease activity measure for systemic lupus erythematosus (SLE), the SLE Disease Activity Score (SLE-DAS), with improved sensitivity to change as compared with SLE Disease Activity Index (SLEDAI), while maintaining high specificity and easiness of use.
Methods We studied 520 patients with SLE from two tertiary care centres (derivation and validation cohorts). At each visit, disease activity was scored using the Physician Global Assessment (PGA) and SLEDAI 2000 (SLEDAI-2K). To construct the SLE-DAS, we applied multivariate linear regression analysis in the derivation cohort, with PGA as dependent variable. The formula was validated in a different cohort through the study of: (1) correlations between SLE-DAS, PGA and SLEDAI-2K; (2) performance of SLEDAI-2K and SLE-DAS in identifying a clinically meaningful change in disease activity (ΔPGA≥0.3); and (3) accuracy of SLEDAI-2K and SLE-DAS time-adjusted means in predicting damage accrual.
Results The final SLE-DAS instrument included 17 items. SLE-DAS was highly correlated with PGA (r=0.875, p<0.0005) and SLEDAI-2K (r=0.943, p<0.0005) in the validation cohort. The optimal discriminative ΔSLE-DAS cut-off to detect a clinically meaningful change was 1.72. In the validation cohort, SLE-DAS showed a higher sensitivity than SLEDAI-2K (change ≥4) to detect a clinically meaningful improvement (89.5% vs 47.4%, p=0.008) or worsening (95.5% vs 59.1%, p=0.008), while maintaining similar specificities. SLE-DAS performed better in predicting damage accrual than SLEDAI-2K.
Conclusion SLE-DAS has a good construct validity and has better performance than SLEDAI-2K in identifying clinically significant changes in disease activity and in predicting damage accrual.
- systemic lupus erythematosus
- disease activity
- outcomes research
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Handling editor Josef S Smolen
Contributors DJ, JAPS, AD and LSI contributed to the conception and design of the project, analysis and interpretation of data, and drafting and critical revision of the manuscript. DJ and LSI also contributed to patient follow-up at CHUC Lupus Cohort. AM and CH contributed to the design of the project, statistical analysis and interpretation of data, and critically revised the manuscript. MZ, ML and LI contributed to patient follow-up, and analysis and interpretation of data, and critically revised the manuscript. LSI and LI scored the disease measures in CHUC Lupus Cohort and Padova Lupus Cohort, respectively.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Obtained.
Ethics approval This study was approved by the Ethics Committee of the ‘Centro Hospitalar e Universitário de Coimbra’, Coimbra, Portugal and ‘Azienda Ospedaliera-Università degli Studi di Padova’, Padova, Italy. Informed consent was obtained from all patients before any study procedures.
Provenance and peer review Not commissioned; externally peer reviewed.
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