Abstract
Background and aims To develop and validate a new index, SLEDAI-2K Glucocorticoids Index (SGI), to accurately describe disease activity while accounting for GC doses.
Methods Phase 1: Identification of patient scenarios followed in a longitudinal cohort. Phase 2: Equation’s derivation explaining the association between SLEDAI-2K and GC dose while using physician global assessment (PGA) as Gold Standard. Phase 3: Validation of SGI against SLEDAI-2K in active patients.
Scenarios were identified using the top 13 organ involvement combinations, then patients were grouped into 7 categories based on GC dose and 10 patients per category were selected. Scenario information included: SLEDAI-2K score, organ involvement combination and GC dose.
3 rheumatologists ranked disease activity with PGA. An independent cohort was used for the validation in phase 3. We hypothesised that in patients with improvement/worsening by SLEDAI-2K, the change in SLEDAI-2K and SGI will correlate.
Results Scenario development is summarised in table 1. 131 scenarios were ranked by 3 rheumatologists leading to 393 records. Perfect LS agreement was achieved; ICC (2, k) of 0.89 (95% CI: 0.83, 0.89). A quadratic linear regression model relating GC and SLEDAI-2K was structured; SGI score=SLEDAI-2K score+[3.65+0.29*GC–0.0027(GC*GC)]. The weight score of GC doses was derived (Table 2). Construct Validity: 109 of the 158 patients improved, 38 remained unchanged, 11 worsened. SLEDAI-2K and SGI correlated highly (r=0.87) and changed in the same direction in patients with improvement/worsening proving the validity of SGI.
Conclusions We developed and validated a novel lupus disease activity index, SGI, that describes disease activity while accounting for GC dose.
