Urine cytology screening for polyoma virus infection following renal transplantation: the Oxford experience

Objective: To review the first year of a monthly urine cytology screening service, introduced to identify renal transplant patients at risk of polyoma virus nephropathy (PVN), at an early, potentially treatable, stage. Methods and results: Monthly urine samples (n = 392) were received from 97/108 transplant recipients in 2005. Of 56 patients with follow-up > 6 months, 20% and 9% had significant (> 10 decoy cells/cytospin) and non-significant positive cytology, respectively. The first positive urine samples occurred most commonly in the second and third month post-transplantation and patients with significantly positive samples had higher 3-month and 6-month serum creatinine levels than patients with negative urine cytology (p < 0.01). Four patients with positive urine cytology had a subsequent positive plasma BK virus PCR; 3/97 patients had biopsy-proven PVN, all in the third month, 1-6 weeks after first positive urine samples. Conclusions: Significant PV viruria is common following renal transplantation with onset usually within the first 3 months. Viruria is associated with worse graft function at 3 and 6 months. The time between urine positivity and clinical PVN is short. More frequent early urine screening would be required to achieve clinical benefit.