The Renal Activity Index for Lupus: Validation for Prediction of Kidney Inflammation in Adult Patients With Lupus Nephritis.

OBJECTIVE: To evaluate the ability of the Renal Activity Index for Lupus (RAIL) score, a urine biomarker-derived score, to capture and predict the course of active lupus nephritis (LN) in adult patients. METHODS: Available serial urine samples collected up to week 52 from a subset of adults with active biopsy-proven proliferative LN participating in the double-blind randomized ALLURE trial of abatacept (ClinicalTrials.gov: NCT01714817) were used to calculate RAIL scores from creatinine-adjusted urine biomarkers (neutrophil gelatinase-associated lipocalin [NGAL], kidney injury molecule 1 [KIM-1], monocyte chemotactic protein 1 [MCP-1], adiponectin, hemopexin, ceruloplasmin). Discriminative performance of RAIL scores alone over time were compared with urine protein/creatinine ratio (UPCR), kidney function (estimated glomerular filtration rate [eGFR]), and mixed model analysis of RAIL score adjusted for baseline UPCR, eGFR, age, weight, sex, and race, with comparisons by renal response states including complete renal response (CRR), partial renal response but not CRR (PRR-only), and nonresponse (NR). RESULTS: The analysis included 240 patients who contributed 599 samples. At weeks 12/24/52, there were 44/22/15 patients with PRR-only, 27/33/18 with CRR, and 127/61/15 NR. RAIL scores, eGFR, and UPCR improved over time irrespective of abatacept use, but were significantly lower with CRR compared to NR. The eGFR alone had poor accuracy (area under the receiver-operating characteristic curve [AUC] < 0.51) to discriminate renal response. Only after correction of baseline UPCR and eGFR, the RAIL score had excellent accuracy to reflect CRR from other renal response states at the current (AUC = 0.83-0.84) and next visit (AUC = 0.84-0.85) and performed better than UPCR; without correction, UPCR and RAIL score had similarly good accuracy. CONCLUSION: RAIL scores identify active LN and longitudinally predict the course of adult LN. (ClinicalTrials.gov: NCT01714817).