McVey RJ et al. (2004) How long is urinary cytology abnormal after flexible cystoscopy? BJU Int 94: 548–551

Abnormalities in voided urine cytology, including papillary aggregration and enlarged nuclei, are routinely used as markers for bladder neoplasia. Similar changes can be caused by examination of the urinary tract by flexible cystoscopy. Since this method is routinely used in the diagnosis of transitional cell carcinoma of the urinary tract, it is possible that these reactive changes could lead to misdiagnosis of malignancy if urine is analyzed too soon after instrumentation. McVey et al. have carried out a study to determine how quickly after flexible cystoscopy the urine cytology returns to normal.

A total of 48 patients provided urine samples before undergoing flexible cystoscopy. Further samples were provided immediately after the procedure and at 1, 2, 4, 7, 14 and 28 days. Anonymized cytology slides prepared from each sample were then examined by three cytopathologists.

As expected, samples provided immediately after cystoscopy showed a substantial increase in urothelial cells. Accompanying morphological changes included enlarged nuclei and nuclear atypia, formation of papillary clusters, and elongation of cells to form polarized, 'columnar' cells. In most cases, these cellular abnormalities returned to normal 1 day following instrumentation.

The study confirms that the process of flexible cystoscopy produces transient urinary cytological changes suggestive of malignancy. A time interval of 1 day between cystoscopy and cytological examination is usually sufficient to avoid false-positive results. Consequently, McVey et al. recommend that details about the interval from any endoscopic procedure are essential when sending urine for cytological analysis after instrumentation.