Correlations between plasma BK viral load, pathological findings, and prognosis in BK polyomavirus-associated nephropathy after kidney transplantation

Abstract Background BK polyomavirus-associated nephropathy (BKPyVAN) is a significant risk factor for graft loss after kidney transplantation, with pathological staging defined by the Banff Working Group. Although quantitative plasma BK polyomavirus (BKPyV) polymerase chain reaction (PCR) has emerged as a surrogate marker for BKPyVAN diagnosis and prognosis, the correlation between histological findings and PCR-based viral load has not yet been fully elucidated. Methods This single-center retrospective cohort study included patients who had undergone kidney transplantation between 2012 and 2022. The patients were categorized into two groups based on their plasma BK viral loads (PCR values): low (< 100,000 copies/mL) and high (≥ 100,000 copies/mL). The primary endpoint was the correlation between PCR plasma viral load (pvl) and histological pvl score. The secondary endpoints were the correlation between plasma viral load and Δci score (change in ci score since the last biopsy within one year) and a 40% estimated glomerular filtration rate (eGFR) decline since diagnosis. Results Twenty-three BKPyVAN cases were diagnosed among 1165 kidney transplantations during the follow-up period. The histological pvl score was mildly correlated with plasma BK viral load ( r = 0.695, p < 0.001), but not the Δci score ( r = 0.119, p = 0.673). A log-rank test for a 40% eGFR decline-free survival revealed that a higher plasma BK viral load was associated with poorer graft renal function (80.0% versus 31.1%, p = 0.021). Graft prognosis did not differ when stratified by Banff BK classification, pvl score, or Δci score. Conclusions Plasma BK viral load was mildly associated with the pvl score but not Δci score. Additionally, high viral load was significantly associated with an increased risk of a 40% eGFR decline, reflecting poorer graft outcomes.