Combined measurement of serum DNA and urine VP1 messenger RNA in monitoring BK virus replication in kidney graft recipients.

Evaluation of BK virus replication is a fundamental tool in the monitoring of renal transplant recipients. Herein, we investigated the role of urine VP1 messenger RNA (mRNA) quantification and combined measurement of serum DNA and urine VP1 mRNA in 428 kidney allograft recipients. BK viremia and viruria were detected in 24 (5.6%) and 54 (12.6%) patients, respectively. A diagnosis of BKV-associated nephropathy (BKVAN) was established in 2 patients, both within the first year posttransplantation. Based on urine VP1 mRNA measurement, BKV replication was observed in 10 (2.1%) patients, 2 of whom displayed BKVAN. Urine VP1 mRNA was detected in all cases in association with viremia except 5 and in all cases with viruria. No difference among VP1 mRNA levels was noted between the 2 BKVAN patients and the highest values in patients without BKVAN. The urine VP1 mRNA result by analysis using the operating characteristics was not superior to viremia, despite the improvement obtained with the combined measurement of viremia (cut-off, 16,000 copies/mL) and urine VP1 mRNA (>10,000 copies/103 cells). In conclusion, VP1 mRNA measurements may complement viremia and viruria to monitor BKV replication, although its use is limited by its technical complexity in comparison with DNA detection.