Clinical relevance of proteinuria selectivity index and fractional excretion of sodium in patients with nephrotic syndrome

Proteinuria selectivity index (PSI) is a potential tool for histological classification and prediction of treatment response in nephrotic syndrome, but evidence is insufficient. Clinical relevance of fractional excretion of sodium (FENa) in nephrotic syndrome remains largely unexplored. This multicenter retrospective study included patients with nephrotic syndrome who underwent kidney biopsy between January 2012 and June 2022. Optimal cutoffs for predicting complete remission based on PSI and FENa were determined using receiver operating characteristic curves. Patients were divided into two groups using these cutoffs and followed until complete remission. Of the 611 patients included, 177 had minimal change disease (MCD), 52 had focal segmental glomerulosclerosis (FSGS), and 149 had membranous nephropathy (MN). Median (interquartile range) PSI were 0.14 (0.09-0.19) for MCD, 0.33 (0.23-0.40) for FSGS, and 0.20 (0.14-0.30) for MN. FENa were 0.24 (0.09-0.68), 1.03 (0.50-2.14), and 0.78 (0.41-1.28). Patients with low PSI and FENa had a higher incidence of complete remission. Cox regression analyses demonstrated that both parameters were associated with achieving complete remission (HR 2.73 [95% CI 1.97-3.81] and HR 1.93 [95% CI 1.46-2.55], respectively). PSI and FENa may be useful for histological classification and predicting remission in nephrotic syndrome.