Systemic Lupus Erythematosus Disease Activity Index 2000 Responder Index-50: A Reliable Index for Measuring Improvement in Disease Activity

Abstract

To test the interrater and intrarater reliability of the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) Responder Index (SRI-50), an index designed to measure ≥ 50% improvement in disease activity between visits in patients with systemic lupus erythematosus. This was a multicenter, cross-sectional study with raters from Canada, the United Kingdom, and Argentina. Patient profile scenarios were derived from real adult patients. Ten rheumatologists from university and community hospitals and postdoctoral rheumatology fellows participated. An SRI-50 data retrieval form was used. Each rheumatologist scored SLEDAI-2K at the baseline visit and SRI-50 on followup visit, for the same patients, on 2 occasions 2 weeks apart. Physician global assessment (PGA) was determined on a numerical scale at baseline visit and a Likert scale on followup visit. Interrater and intrarater reliability was assessed using intraclass correlation coefficient (ICC) and kappa statistics whenever applicable. Forty patient profiles were created. The ICC performed on 80 patient profiles for interrater ranged from 1.00 for SLEDAI-2K and SRI-50 to 0.96 for PGA. The intrarater ICC for SLEDAI-2K, SRI-50, and PGA scores ranged from 1.00 to 0.86. Substantial agreement was determined for the interrater Likert scale, with a kappa statistic of 0.57. The SRI-50 is reliable to assess ≥ 50% improvement in lupus disease activity. Use of the SRI-50 data retrieval form is essential to ensure optimal performance of the SRI-50. SRI-50 can be used by both rheumatologists and trainees and performs equally well in trained as well as untrained rheumatologists.