AbstractBackground and objectivesThe risk of de novo donor‐specific antibody (dnDSA) development following BK viremia (BKV) or nephropathy (BKN) after kidney transplant remains unclear. We aimed to evaluate the relationships among dnDSA, BKV (BK blood PCR > 15 000 copies), BKN, antibody‐mediated rejection (AMR), and allograft loss.Patients and methodsWe performed a retrospective cohort study of 904 solitary kidney transplant recipients transplanted between 10/2007 and 5/2014. Cox proportional hazards regression with time‐dependent covariates were used to assess the relationships among BKN, isolated BKV, dnDSA, and the subsequent risk of AMR and allograft loss.ResultsIn multivariate analysis, we observed that BKN, but not BKV was a risk factor for dnDSA (HR, 3.18, P = .008). Of the patients with BK nephropathy, 14.0% (6/43) developed dnDSA, which occurred within 14 months of BK diagnosis. DnDSA in this setting remains a risk factor for subsequent AMR (HR 4.75, P = .0001) and allograft loss (HR 2.63, P = .018).ConclusionsBKN is an independent risk factor for development of dnDSA. Improved understanding of the characteristics of patients with BKN who are at highest risk for development of dnDSA would be valuable to customize immunosuppression reduction in this population.