Introduction: Polyoma (BK) nephropathy develops in 5-10% of renal transplant recipients and is a serious complication associated with a high rate of graft dysfunction and loss. The initiation of immunosuppressive agents after transplantation to prevent rejection likely leads to reactivation and proliferation of donor- or host-derived latent BK virus, which resides in the genitourinary tract. Interestingly, nephropathy due to BK virus only develops in kidney allografts and has not been reported in host native kidneys of similarly immunocompromised heart, liver or lung transplant recipients. Thus, it is hypothesized that both local tissue inflammation as well as immunosuppression are requisites for reactivation and proliferation of BK virus. Our aim was to measure whether surgical nephroureteral stent placement at the time of transplantation to facilitate the ureteroneocystostomy was associated with an increased risk for BK viremia. Methods: In 1/06 we initiated a serum screening policy for all newly transplanted patients by obtaining monthly blood testing for BK determination by PCR. Between 1/1/06 and 12/31/08, 175 renal transplants were performed at our institution. Ureteral stents were placed in 95 (54%) recipients (group A) while stents were not used in 80 (46%) patients (group B). The decision to utilize a ureteral stent was based on local operative findings and surgeon preference. Recipients in both groups were treated with the same immunosuppressive protocol consisting of Thymoglobulin induction, followed by maintenance therapy with prograf, mycophenolate mofetil and prednisone or rapamune. Demographics between the two groups were similar with respect to age, gender, ethnicity, diabetes and incidence of acute rejection.

Results: Serum PCR became positive for BK virus in 30/175 patients after transplantation (17%). Mean time to a positive PCR post-transplant was 5 months (2-11 mos.). PCR results segregated by ureteral stenting identified that BK viremia was detected in 23/95 (24%) group A patients compared to only 7/80 (9%) group B patients (P<0.05).

Conclusion: Intraoperative placement of ureteral stents during renal transplantation is associated with a significantly increased risk of BK viremia. In light of this finding serious consideration should be given to minimize the utilization of ureteral stents or, in cases where stent placement is required due to operative conditions, early removal and aggressive screening for BK viremia.