The value of urinary decoy cells finding in patients with kidney transplantation.

Childhood infection with polyomaviruses leads to a life-long latent infection of renal and urinary tract epithelia. Replication in the reno-urinary epithelium is associated with viral cytopathic changes such as nuclear inclusions and decoy cells. During the 2005-2009 period, cytological urine analysis was performed in 154 samples (94 male and 60 female) from patients with kidney transplantation (n = 19), simultaneous pancreas-kidney transplantation (SPKT) (n = 9) and simultaneous kidney and liver transplantation (n = 2). Urine samples were analyzed monthly following transplantation according to the protocol. The period from transplantation to the first occurrence of decoy cells in the urine and the period of decoy cell persistence in the urine were assessed. The presence of decoy cells (< 10 and > 10 decoy cells) and red blood cells (< 20 E, 20-100 E and > 100 E) per cytospin smear was semiquantitatively determined, along with analysis of inflammatory cells (neutrophilic granulocytes) and fungi. In patients with decoy cells detected, their sensitivity, specificity, and negative and positive predictive value for BK virus nephropathy were calculated. Correlation of the study parameters was estimated by use of Kruskal-Wallis test (Statistica 7.1, StatSoft Inc., Tulsa, USA). Decoy cells were found in 30 patients (20 male and 10 female), age median 40 (range 16-69) years, at a mean of day 115 (range day 5-747) post transplantation, whereas their presence was recorded for a mean of 141 (range 77-771) days. Immunohistochemical staining of kidney biopsy sample for polyomavirus (SV40 large T-antigen) yielded positive reaction in 2/30 (7%) patients. Erythrocyturia was present in 29/30 patients with decoy cells. The number of decoy cells per cytospin smear generally ranged less than 10 in 25/30 patients, whereas more than 10 decoy cells per cytospin smear were only recorded in 5/30 patients. Immunohistochemistry produced positive finding for BK virus in one patient with SPKT and simultaneous kidney and liver transplantation each, which was statistically significantly more common as compared with patients with kidney transplantation alone (p = 0.0244). Immunohistochemical positivity for BK virus was more significant in cases with more than 10 decoy cells detected in cytospin smear (p = 0.013). In BK nephropathy, the finding of urinary decoy cells showed a 100% sensitivity, 84% specificity, 100% negative predictive value and 6% positive predictive value. BK virus nephropathy remains a significant post transplantation complication.