Diagnostic utility of urine cytology in detection of decoy cells in renal transplant patients: Report of five cases and review of literature.

BK polyoma virus (PV) is one of the commonest post-transplant viral infections, affecting approximately 15% of renal transplantation recipients, leading to graft failure in more than half of cases. The epithelial cells with polyoma viral inclusions in urine cytology specimens are termed "decoy cells" to caution pathologists not to misdiagnose these cells as cancer cells. The infected cells in urinary sediments are characterized by enlarged nucleus, basophilic intranuclear homogenous inclusions, and ground glass chromatin, which may cause diagnostic error in urine cytology. We report five cases of renal transplant patients, in which urine sample was positive for decoy cells. Routine urine cytology of post renal transplant patients with worsening renal function is a useful screening procedure to rule out PV reactivation, before ascertaining transplant rejection. Its cost-effectiveness in addition to the short processing time makes it an invaluable tool in the evaluation of transplant recipients with symptoms suggestive of graft rejection.