Quantitation of BK virus load in serum for the diagnosis of BK virus-associated nephropathy in renal transplant recipients

BK virus-associated nephropathy is an increasingly recognized cause of graf t dysfunction among kidney transplant recipients, and definitive diagnosis requires renal biopsy. By using a newly developed, quantitative, real-time polymerase chain reaction (PCR) assay for BK virus DNA, a retrospective ana lysis was done of sequential serum samples (n = 28) from 4 transplant recip ients with histopathologically documented BK virus nephropathy and from sam ples (n = 76) from 16 transplant recipient control patients. BK virus DNA w as detected in serum samples from all 4 case patients versus 0 of 16 contro l patients (P < .0001, Fisher's exact test) at a median of 32 weeks (range, 17-61 weeks) before the diagnosis of BK virus nephropathy. BK virus load d ecreased in 3 of 3 patients after the reduction of immunosuppression and/or nephrectomy. It is concluded that quantitative PCR for BK virus DNA in ser um is useful both for identifying transplant recipients at risk for BK viru s nephropathy and for monitoring the response to therapy.