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Proteinuria selectivity index as a prognostic biomarker in lupus nephritis

Objectives The selectivity index has been proposed in predicting the response to immunosuppressive therapy in nephrotic syndrome and other primary kidney disorders. The aim of this study was to elucidate the predictive value of the selectivity index for the treatment response and renal outcome in patients with lupus nephritis. Methods Forty-four patients with lupus nephritis with selectivity index available at the time of renal biopsy were divided into two groups according to the cut-off value of the selectivity index determined by a receiver operating characteristics curve to differentiate treatment responders from non-responders. The baseline characteristics, overall response rate and renal functional outcome were studied retrospectively, and compared between the two groups. Prognostic factors for achieving remission were identified. Results The cut-off value of the selectivity index was 0.167. The low selectivity index (<0.167) and the high selectivity index (≥0.167) group included 24 and 20 patients, respectively. The overall response rate was significantly higher (88% vs. 50%, P = 0.007) and the rate of progression to end-stage renal disease was lower in the low selectivity index group (0% vs. 15%, P = 0.049). More patients in the high selectivity index group had chronic lesions on renal biopsy (P = 0.002). The selectivity index was the prognostic factor for achieving overall response based on a multivariate analysis (P = 0.020). Conclusions A selectivity index ≥0.167 was a strong predictor for a poor treatment response and the presence of chronic lesions on renal biopsy. Further exploration with a larger cohort and longer follow-up period is warranted.