Monitoring of BK viral load in renal allograft recipients by real-time PCR assays.

BK virus (BKV) is a nonenveloped, double-stranded DNA virus of the polyomavirus family that primarily affects immunocompromised people. BKV may cause nephropathy in renal transplant recipients receiving immunosuppressive therapy, resulting in renal dysfunction and, possibly, graft loss. Monitoring of BK viral load in urine and blood has been used as a surrogate marker of BKV nephropathy (BKVN). Although real-time polymerase chain reaction (PCR) is the method of choice, currently there is no US Food and Drug Administration-approved or standardized BK viral load assay. Different PCR assays vary significantly in sample types, DNA extraction method, PCR primers and probes, and reference materials used to generate a standard curve. These differences can affect the accuracy, specificity, and dynamic ranges of various real-time PCR assays. These analytic differences cause difficulty in comparing test results, making it impossible to establish universal standardized cutoff values that correlate with clinical manifestations of BKVN. In this review, we summarize real-time PCR assays used for managing BKVN.