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Clinical usefulness of BK virus plasma quantitative PCR to prevent BK virus associated nephropathy

The present study investigated the clinical usefulness of plasma real‐time polymerase chain reaction (PCR) (plasma‐PCR) in the prevention of BK virus‐associated nephropathy (BKVAN). First, we investigated the diagnostic value of plasma BK‐PCR, urine BK‐PCR, and urine cytology for the prediction of BKVAN retrospectively. Then we designed a prospective study of regular plasma‐PCR monitoring and pre‐emptive immunosuppression (IS) reduction based on the result. In the retrospective cohort, the prevalence of BKVAN was 3.7% (14/379) and the positive rate of decoy cells, urine‐PCR (>1 × 1010 copies/ml), and plasma‐PCR (>1 × 104 copies/ml) was 18.6%, 11.1%, and 5.5%, respectively. Plasma‐PCR was superior to urine‐PCR or urine cytology in specificity and positive predictive value for detection of BKVAN. In prospective study, regular monitoring of plasma‐PCR detected significant BKV viremia in 8.3% (12/145) and BKVAN in 1 patient (0.6%). After IS reduction, BKV viremia was eliminated in 91.6% (11/12) within 103 days (25–254). In patients with viremia, the frequency of acute rejection did not increase and allograft function did not differ significantly compared with those in patients without viremia during the first year post‐transplant (P > 0.05, in both). Plasma‐PCR is useful to predict an increased risk for BKVAN, and regular monitoring is effective to prevent the development of BKVAN.