Systemic Lupus Erythematosus Disease Activity Index 2000 Responder Index 50: Sensitivity to Response at 6 and 12 Months

Objective: The SLEDAI 2000 (SLEDAI-2K) Responder Index 50 (SRI-50) is a novel index that measures ≥ 50% in each of the 24 descriptors of SLEDAI-2K and generates a total score reflecting disease activity overall. The SLE Responder Index (SRI) has been successfully used to identify responders in recent trials. This is the first study to evaluate the ability of SRI-50 to identify responders, defined as patients who had a clinically important improvement over their baseline value over 12 months. We compared the performance of SRI-50 with that of SLEDAI-2K and SRI at 6 and 12 months in identifying responders.

Methods: Patients with active disease were followed for 6-12 months and assessed using SLEDAI-2K, British Isles Lupus Assessment Group and Physician Global Assessment. We identified SLEDAI-2K responders, SRI-50 responders and SLE responders at 6 and 12 months. We determined whether patients who are defined as SRI-50 responders are true responders when SRI is considered the gold standard.

Results: Among the 103 patients studied, the percentage of responders at 6 and 12 months was 44 and 51% when determined by SLEDAI-2K and 43 and 51% by SRI, respectively. The percentage of SRI-50 responders at 6 and 12 months was 51 and 58%, respectively.

Conclusion: SRI-50 identified more responders compared with SLEDAI-2K and SRI at 6 and 12 months. SRI-50 is a valid responder index that can be used independently to identify patients with true clinically important improvement.