Ten tips on management of BK nephropathy in kidney transplant patients.

Management of BK virus after kidney transplantation remains challenging, as recently published updated guidelines identify ongoing gaps in the evidence. In this article we present tips for management based on evidence and clinical experience. Testing blood for BK virus by polymerase chain reaction should be part of the workup for any patient with significant deterioration in kidney transplant function. All kidney transplant biopsies should be tested by immunohistochemistry for the presence of SV40 large T antigen if there are features of tubulointerstitial inflammation on light microscopy. A transplant kidney biopsy that does not include medulla does not exclude BK virus-associated nephropathy (BKVAN). Tubulointerstitial inflammation with positive SV40 staining and undetectable BK virus in the blood implies a different polyomavirus nephropathy such as JC virus. Clinicians should consider the evidence carefully before deciding whether or not to adopt a BK viraemia screening strategy in their unit. If a strategy of screening for BK viraemia in the absence of transplant dysfunction is adopted, then it makes sense to target the first year and for screening to be at least every 4 weeks. The optimal reduction in immunosuppression in response to BK viraemia or BKVAN has not been established by clinical trials. A rapid decline in BK viral load after reduction in immunosuppression appears to be a strong risk factor for impending T cell-mediated rejection. Clinical trials of the addition of potentially effective anti-polyomavirus agents including leflunomide, fluoroquinolones, intravenous immunoglobulin concentrate, cidofovir and statins have not shown benefit. BK viraemia or BKVAN recurrence after viral clearance is rare.