Urinary Decoy Cell Grading and Its Clinical Implications

BACKGROUND Examination of urine for decoy cells (DCs) is a useful screening test for polyomavirus (PV) activation. We explored the significance of the amount of DCs in persistent shedding, PV nephropathy and acute rejection. METHODS A case-controlled study was performed in 88 renal allograft patients who had DCs detected at least once in four or more urine samples. RESULTS Fifty one patients were classified into the high-grade shedding group (HG) and 37 patients into the low-grade shedding group (LG) according to DC shedding (≥10 or <10 DCs/10 high power field [HPF]). DC shedding of more than three consecutive months was significantly more prevalent in the HG as compared with their LG counterparts (p<0.0001). Urinary DCs were present for more than one year in 29.4% of the HG and 8.1% of the LG. Real-time polymerase chain reaction for PV was higher in both urine (51.4% vs. 11.1%) and plasma (9.1% vs. 0%) of the HG than the LG. The prevalence of PV nephropathy was higher in the HG than the LG (p=0.019). However, there was no significant difference in the prevalence of acute rejection. CONCLUSIONS Shedding of ≥10 DCs/10 HPF is associated with sustained shedding, polymerase chain reaction positivity and PV nephropathy, but not a predictor of acute rejection.