Periodic assessment of urine and serum by cytology and molecular biology as a diagnostic tool for BK virus nephropathy in renal transplant patients

Objective: To investigate the significance of polyomavirus (PV) viruria and viremia by morphologic, immunohistochemical and molecular analysis (multiplex nested-polymerase chain reaction) in renal transplant patients. Study Design: Urine (n = 328), serum (n = 53) and renal biopsies (n = 24) from renal transplant patients (n = 106) were studied. Results: Decoy cells were found in 53 samples (16%) from 19 patients (18%); viral DNA was amplified in all urinary samples and disclosed BK virus (BKV) (n = 24), JC virus (JCV) (n = 16), and JCV and BKV DNA (n = 13). BKV was the prevailing genotype in patients with a high frequency of decoy cell excretion (p = 0.001). JCV excretion correlated with a low number (p = 0.01) and BKV with a high number of decoy cells (p = 0.003). PV DNA was amplified from 30/53 serum samples (56.6%); BKV was the prevailing genotype (p = 0.04). On 24 renal biopsies (18 from the decoy cell-negative and 6 from the decoy cell-positive group) PV nephropathy (PVN) was identified and BKV DNA amplified in 4 biopsies, all from the group with a high frequency of decoy cell excretion. PVN was not identified in renal biopsies from the decoy cell-negative group. Conclusion: PV infection is frequent in renal transplant patients. The BKV genotype in urine and serum is significantly related to a high frequency and high number of decoy cells. PVN occurs only in patients with BKV viremia and a high number and frequency of decoy cell excretion in urine. In the absence of decoy cells, PVN can be excluded. Cytologic analysis of urine is an important diagnostic tool for screening renal transplant patients at risk of PVN.