Urine cytology

Urine cytology

• Urine collection for cytology: Exfoliated cells lying in urine which has been in the bladder for several hours (e.g. early morning specimens) or in a urine specimen that has been allowed to stand for several hours, are degenerate. Such urine specimens are not suitable for cytological interpretation. Cytological examination can be performed on bladder washings (using normal saline) obtained from the bladder at cystoscopy (or following catheterization) or from the ureter (via a ureteric catheter or ureteroscope). The urine is centrifuged and the specimen so obtained is fixed in alcohol and stained by the Papanicolaou technique.
• Normal urothelial cells are shed into the urine and under microscopy their nuclei appear regular and monomorphic (diffuse, fine chromatin pattern, single nucleolus).
• Causes of a +ve cytology report (i.e. abnormal urothelial cells seen high nuclear:cytoplasmic ratio, hyperchromatic nuclei, prominent nucleoli):
  • urothelial malignancy (TCC, squamous cell carcinoma, adenocarcinoma)
  • previous radiotherapy (especially if within the last 12 months)
  • previous cytotoxic drug treatment (especially if within the last 12 months; e.g. cyclophosphamide, busulphan, cysclosporin)
  • urinary tract stones
• Renal adenocarcinoma (clear cell cancer of the kidney) usually does not exfoliate abnormal cells, though occasionally clusters of clear cells may be seen, suggesting the diagnosis.
• High-grade urothelial cancer and carcinoma in situ exfoliate cells which look very abnormal, and usually the cytologist is able to indicate that there is a high likelihood of a malignancy. Low-grade bladder TCC exfoliates cells which look very much like normal urothelial cells. The difficulty arises where the cells look abnormal, but not that abnormal here the likelihood that the cause of the abnormal cytology is a benign process is greater.
• Sensitivity and specificity of +ve urine cytology for detecting TCC of the bladder depends on the definition of +ve if only obviously malignant or highly suspicious samples are considered +ve, then the specificity will be high. Urine cytology may be negative in as many as 20% of high-grade cancers. If  atypical cells are included in the definition of abnormal, the specificity of urine cytology for diagnosing urothelial cancer will be relatively poor (relatively high number of false +ves) because many cases will have a benign cause (stones, inflammation).