The Banff 2009 Working Proposal for Polyomavirus Nephropathy: A Critical Evaluation of Its Utility as a Determinant of Clinical Outcome

Clinical outcome in BK virus nephropathy (BKVN) was examined in relation to clinical and histologic parameters with reference to the Banff Working Proposal 2009, which emphasizes tubular injury and viral load. Seventy one patients were evaluated in three eras: (i) Era‐I: No BKV PCR performed (n = 36), (ii) Era‐II: PCR performed for rising creatinine (n = 24) and (iii) Era III: PCR performed for routine screening (n = 11). Six of seventy‐one (8.4%) patients were classified as Class A, 46/71 (64.8%) as Class B and 19/71 (26.8%) as Class C. Banff class A never occurred in Era‐I. It is a heterogeneous class that includes biopsies with inflammation that have hitherto been included in Class B. Higher inflammation, but not tubular injury, nor histologic viral load correlated with worse creatinine at 3 months. On long‐term follow‐up, class C associated with graft loss (hazard ratio 2.45, p = 0.03). Clearance of viremia was associated with better graft survival at 5 years (46.0% vs. 25.0%). Viruria clearance was infrequent (15.6%). In conclusion, the clinical utility of the Banff Working Proposal 2009 derives from scoring of fibrosis and not extent of tubular injury or viral cytopathic effect. The proposal is not superior to existing schemas that include assessment of inflammation, which is a well‐known prognostic marker in other renal allograft diseases. This evaluation of the Banff Working Proposal for staging polyomavirus nephropathy indicates that the proposal is not superior to existing staging systems, and that consideration should be given to including the degree of inflammation into the assessment of biopsies.