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URINE CYTOLOGY AS A SCREENING TOOL FOR BK VIRUS NEPHROPATHY: PRELIMINARY FINDINGS IN 350 SAMPLES

Background: BK virus allograft nephropathy (BKVAN) is caused by reactivation of BK polyomavirus and often leads to graft failure due to unsuccessful treatment. Screening and early detection with surrogate markers of viral replication are critical to guide preventative strategies. Method: We prospectively evaluated the performance of urinary decoy cells, identified in ThinPrep processed specimens, and SV40T immunochemistry, performed on cell block preparations, to predict BKVAN (defined by reference histology standard, n = 350), in comparison with quantitative viraemia in kidney transplant recipients undergoing routine screening. The decoy cells were then quantified per 10 HPF. Results: Decoy cells occurred in 14.8% of samples, with a sensitivity of 71.4%, specificity of 87.7%, positive predictive value (PPV) of 22.2% and negative predictive value (NPV) of 98.6% to predict BKVAN. Quantification of decoy cells improved the PPV to 53.8% (≥10 cells/10 HPF), comparable to quantitative viraemia of 52.2% (≥104 copies/mL). SV40T staining of urinary cell blocks provided 100% sensitivity and 91.5% specificity, however insufficient material hampered cell block preparation in many samples. Combinations of decoy cell and viraemia in a diagnostic matrix further improved BKVAN prediction. Conclusion: Our preliminary findings show both quantified decoy cells and viraemia are acceptable surrogate markers of early BK viral replication for screening of kidney transplant recipients.