Monitoring of Polyomavirus BK Virus Viruria and Viremia in Renal Allograft Recipients by Use of a Quantitative Real-Time PCR Assay: One-Year Prospective Study

Abstract

ABSTRACT We have developed a real-time quantitative PCR (rt-QPCR) assay to detect and kinetically monitor BK virus viruria and viremia in renal transplant recipients (RTRs). A total of 607 urine and 223 plasma samples were collected from 203 individuals including those with BK virus-associated nephropathy (BKVAN) ( n = 8), those undergoing routine posttransplant surveillance (SV) ( n = 155), those with nontransplant chronic kidney disease (NT-CKD) ( n = 20), and healthy living kidney donors (LD) ( n = 20). The rt-QPCR assay was found to be highly sensitive and specific, with a wide dynamic range (2.4 to 11 log 10 copies/ml) and very good precision (coefficient of variation, ∼5.9%). There was a significant difference in the prevalences of viruria and viremia between the BKVAN (100% and 100%) and SV (23% and 3.9%) groups ( P < 0.001). No viruria or viremia was detected in LD or in NT-CKD patients. The median (range) peak levels of BK virus viruria and viremia, in log 10 copies/ml, were 10.26 (9.04 to 10.83) and 4.83 (3.65 to 5.86) for the BKVAN group versus 0 (0 to 10.83) and 0 (0 to 5.65) for the SV group, respectively ( P < 0.001). When the BK virus load in the urine was <7.0 log 10 copies/ml, no BK virus viremia was detected. When the BK virus load in the urine reached 7.0, 8.0, 9.0, and ≥10.0 log 10 copies/ml, the corresponding detection of BK virus viremia increased to 20, 33, 50, and 100%, respectively. We propose monitoring of BK virus viruria in RTRs, with plasma BK virus load testing reserved for those with viruria levels of ≥7.0 log 10 copies/ml.