How reliable is conventional urinary cytology in post-transplant patients?

Factors like cold, flushing solutions, ischemia and reperfusion may alter the microscopic appearance of transitional cells leading to falsely positive results of urinary cytology in patients after kidney transplantation. After seeing 1 patient presenting with two consecutive highly suspicious cytology specimens 3 days after transplantation and no sign of urothelial tumor at retrograde urography, we analyzed the cytological picture of transitional cells in post-transplant patients.

We investigated 31 urine specimens of 11 patients undergoing kidney transplantation preoperatively (if possible) and on days 1, 3 and 9 postoperatively. Microscopic cytology was performed by using Papanicolaou's criteria: 0 - no cytology possible (no cells), I+II - negative cytology, III - doubtful, IV - suspicious for tumor, V - tumor cells. All microscopic examinations were performed by one experienced senior pathologist.

Mean patient age was 55.8 (+/- 17.5) years, mean residual diuresis 856 (+/- 636) ml, mean cold ischemia time 13.6 (+/- 6.4) h, mean creatinine level on day 1: 582 microM/l, day 3: 533 microM/l and day 9: 259 microM/l. None of the urinary cytology results were suspicious for malignant transformation (Papanicolaou I+II). No patient presented signs of urothelial malignancy after a mean follow-up of 3 months.

Although microscopic urinary cytology may be falsely positive in 1-12% of non-transplanted patients due to urothelia atypia, inflammation or radiation/chemotherapy, the present study suggests that conventional microscopic cytology examinations in post-transplant patients are not heavily altered and do not lead to an increased false-positive rate.