Objectives: There is an unmet need for accurate and user-friendly definitions of systemic lupus erythematosus (SLE) disease activity and remission. We aimed to derive and validate the SLE Disease Activity Score (SLE-DAS) definitions for disease activity categories and clinical remission state.
Methods: Derivation was conducted at Padova Lupus Clinic (Italy). Validation was prospectively performed at Cochin Lupus Clinic (France) and by post hoc analysis of BLISS-76 trial. At each clinic, an expert classified patients in three categories: remission, mild or moderate/severe activity. The SLE-DAS cut-offs were derived using the receiver operating characteristic curve analysis in Padova cohort; its performance was assessed against expert classification in Cochin cohort and British Isles Lupus Assessment Group (BILAG) index in BLISS-76. Gold standard for clinical remission state was the fulfilment of Definition Of Remission In SLE. A Boolean and an index-based definitions of remission were sustained by chi-square automatic interaction detection algorithm. An SLE-DAS online calculator was developed and tested.
Results: We included 1190 patients with SLE: 221 in the derivation cohort and 969 in the validation cohorts (150 from Cochin; 819 from BLISS-76). Derived cut-offs were: remission, SLE-DAS ≤2.08; mild activity, 2.08<SLE-DAS≤7.64; moderate/severe activity, SLE-DAS >7.64. Regarding validation in Cochin cohort, sensitivity and specificity are above 90%, 82% and 95% for remission, mild and moderate/severe activity, respectively. The SLE-DAS Boolean-based and index-based remission showed sensitivity of 100% and specificity above 97%.
Conclusion: The SLE-DAS is an accurate and easy-to-use tool for defining SLE clinical remission state and disease activity categories, validated against expert assessment and BILAG.
Keywords: autoimmune diseases; disease activity; outcomes research; systemic lupus erythematosus.
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