A novel histologic index for polyomavirus nephropathy in comparison with the Banff scoring system: Clinical validation, prognostic implication, and correlation with plasma viral load

BK Polyomavirus nephropathy (PVN) with definitive diagnosis on biopsy, presents incidentally or with varying degrees of graft dysfunction. Banff working group on PVN has proposed a novel scoring system in renal biopsies, to identify patients with higher risk of graft failure. In this study, we attempted to validate the Banff scoring system at index biopsies and correlate with a novel index score, plasma BK-virus load and graft outcome. 48 patients with index biopsies of PVN diagnosed from 2019 to 2022, with simultaneous plasma BKV-virus loads and SV-40 stains were chosen. Biopsies were scored for Banff PVN Class and by novel PVN index. Inter-observer reproducibility was tested between 3 renal pathologists for all parameters and findings were correlated with graft outcome, in a median follow-up of 42 months. Banff PVN classes 2 and 3 and novel index 3 were associated with higher percentage of graft failure and persistent viremia. The novel index score showed a stronger and consistent temporal association with plasma BK-virus levels. Kappa scores revealed a 68 % agreement for Banff PVN class scoring. Our study highlights the prognostic utility of Banff PVN scheme and novel PVN index in correlation with plasma BKV viremia and graft outcome.