Systemic Lupus Erythematosus Disease Activity Score (SLE-DAS) enables accurate and user-friendly definitions of clinical remission and categories of disease activity

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.