Significance of polyomavirus detection in urine cytology: an update

Polyomavirus-associated (BK virus) nephropathy (BKVAN) arises in 1–8% of renal allografts, with an associated risk of graft damage or even graft loss. In the early post-renal transplant months, BKVAN is a key differential diagnostic consideration significantly overlapping with acute rejection. There are multiple modalities available to aid in BKVAN diagnosis including urine cytology, molecular tests of urine and plasma, renal biopsy, and adjunctive immunochemistry. Urine cytology and detection of BK viruria or viraemia (often by real-time PCR) are accepted screening modalities; however, in recent years molecular tests have been increasingly utilized to identify patients at high risk for BKVAN. This review article will comparatively discuss tissue based and molecular methods for BKVAN diagnosis. Key differentiating morphologic features and adjunctive tests will be assessed regarding clarification of common diagnostic pitfalls.