Screening for BK Viremia Reduces But Does Not Eliminate the Risk of BK Nephropathy: A Single-Center Retrospective Analysis

Background. This study reviewed the outcomes of a screening protocol for BK viremia to determine if early diagnosis, followed by immunosuppression minimization, would prevent progression to nephropathy and graft loss. Methods. This review included 369 renal transplant recipients tested for BK virus at serial time points after transplantation. Management included immunosuppression minimization plus cidofovir treatment for BK nephropathy. Results. Recipients received tacrolimus-based immunosuppression, with 8% prednisone-free and 6% who received desensitization. With a mean follow-up of 22 +/- 10 months, 16% (n=57) of recipients became BK viremia positive. The median (range) time to diagnosis was 3 (1-17) months. Because renal biopsy was performed selectively, 59% of recipients underwent biopsy, with 47% showing BK nephropathy. Seventy-four percent of recipients cleared the virus at a median (range) time of 9 (3-33) months, with four grafts lost to BK nephropathy. Cidofovir-treated recipients displayed a higher viral load at diagnosis but showed equivalent renal function at last evaluation. In multivariate analysis, recipient age, Asian ethnicity, deceased donor, and prednisone use were factors independently associated with BK viremia. Actuarial survival of BK-positive grafts was worse than that of BK-negative grafts (P<0.01, log-rank test). At 9 and 12 months, the mean estimated glomerular filtration rate of the BK-positive group was lower than that of the BK-negative cohort (P=0.02). Conclusions. Despite using a screening protocol combined with immunosuppression minimization, BK-positive recipients had a greater risk of graft loss and impaired function than recipients free of infection. Future investigations should focus on practices to prevent BK viremia.