Determination of viremia cut-off for risk to develop BKPyV-associated nephropathy among kidney transplant recipients.

BACKGROUND: BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN) is a consequence of BKPyV replication in the urinary tract in kidney transplant recipients (KTR). OBJECTIVES: The objectives were to determine the prevalence of BKPyV replication and BKPyVAN, risk factors associated to sustained viremia and BKPyVAN, and viremia cut-off that best predict the occurrence of sustained viremia and nephropathy in KTR of a single University Hospital Kidney Transplant Center. PATIENTS AND METHODS: All KTR undergoing transplantation from August 2010 to December 2011 were enrolled and monitored up to 2 years posttransplantation for BKPyV viruria by decoy cells shedding or polymerase chain reaction (PCR) and viremia by PCR. Kidney biopsy was indicated if sustained viremia (two or more viremia above 10 000 copies/mL) to confirm BKPyVAN diagnosis. RESULTS: In this study, 326 transplants were performed and 246 patients were included. Prevalence of viruria was 36.9%, viremia 22.3% and nephropathy 3.2%. Male gender was the only risk factor associated to sustained viremia or nephropathy. Cut-off value of viremia that best discriminates the progression to sustained viremia and to BKPyVAN was 37 488 and 44 956 copies/mL, respectively. CONCLUSIONS: Prevalence of viruria, viremia, and nephropathy were similar to those reported in literature but the cut-off value of viremia that best discriminates the risk of progression to nephropathy was greater than the value usually reported, which is 10 000 copies/mL.