Longitudinal Dynamics of BK Polyomavirus Replication After Kidney Transplantation: From BKPyV DNAuria to BKPyV DNAemia and Individualized Immunosuppressive Management

BK polyomavirus (BKPyV) replication is a major post-transplant complication. Although DNAuria usually precedes plasma DNAemia, its predictive value and relationship to immunosuppressive management remain unclear. This retrospective study included 181 kidney transplant recipients followed for 24 months. Clinically significant BKPyV replication was defined as urinary BKPyV DNA ≥ 10⁷ copies/mL and/or confirmed plasma BKPyV DNA ≥ 10³ copies/mL. Risk factors and changes were analyzed using logistic regression, generalized estimating equations, linear mixed-effects models and time-dependent Cox regression. Clinically significant BKPyV replication occurred in 43 recipients (23.8%). Recipient age independently predicted BKPyV replication (odds ratio 1.04 per year, 95% confidence interval 1.00–1.07; P = 0.040). Significant BKPyV DNAuria predicted subsequent plasma DNAemia (odds ratio 4.36, 95% confidence interval 1.45–13.08; P = 0.009), with a negative predictive value > 90%. Its predictive value was strongest early after transplantation and declined over time. BKPyV-positive recipients received lower mycophenolate mofetil doses, with similar tacrolimus exposure. BKPyV DNAemia cleared in most evaluable recipients, with no statistically significant differences between groups in biopsy-proven acute rejection, de novo donor-specific antibody development or graft function. Lagged analyses showed no independent association between mycophenolate mofetil dose reduction and viral kinetics. Recipient age independently predicts BKPyV replication. Significant DNAuria is an early predictor of plasma DNAemia and may improve surveillance. Lower mycophenolate mofetil exposure with comparable tacrolimus exposure characterized management of BKPyV-positive recipients; however, the observational design precludes attributing viral clearance or immunological safety to mycophenolate mofetil reduction.