Collection of specimens
Voided urine is the simplest method of collection. Early morning urine should be avoided because of the poor morphological details shown by the cells exfoliated during the night and being exposed to urine for several hours. The best is a mid-morning specimen. The sample should be sent to the laboratory as soon as possible. If a short delay is inevitable the container should be kept in a refrigerator. In case of longer delay some alcohol should be added to the sample.
Catheter specimens. This method facilitates the collection of good samples without contamination and is the method of choice when urine must be collected from one of ureters. The disadvantages are that it is an invasive procedure with the possibility of detaching sheets of urothelial cells with the tip of the catheter. These cells can mimic cells from a papillary tumour cytologically.
Bladder washings. This is also known as barbotage. It is performed by irrigating the bladder with a saline or fixative solution. It has the same disadvantages of catheter specimens, but the cellularity obtained and the cell preservation are very good and superior to voided urine.
A good fixative fluid to perform bladder washing is Espostis fixative. 100 ml of Espostis fixative contains 10 ml of acetic acid, 45 ml of methanol and 45 ml of deionised water. The fluid is used to irrigate the bladder, collected in a 250 ml bottle and then sent to the laboratory. It is centrifuged to obtain a pellet, the supernatant discarded and 2 drops of pectin added to the pellet to facilitate detachment from the centrifuge tube wall. Finally two drops from the cell pellet are placed on a microscope slide, air-dried at room temperature and stained according to the Papanicolaou method. Two or more slides are prepared for each case.
Other preparation techniques
Voided or catheterized urine specimens can be processed for microscopy by one of the following methods.
- Centrifugation followed by cytocentrifugation. Alcohol fixation is necessary before staining with the Papanicolaou method. Cytocentrifugation should produce a sample which is almost a monolayer of cells measuring about 6 mm in diameter.
- Direct smears. They are easier to prepare but show usually scanty cellularity.
- Membrane filter preparations. They show very good cellularity, but are difficult to prepare.
Preparations are fixed in alcohol and stained using the Papanicolaou stain.
Monolayer preparations such as ThinPrep (Cytyc Corporation, Boxborough, MA, USA) are also used to prepare urine samples. The preservation of the cells is usually very good and the procedure is easier than the filter method. The cost, at the moment, is probably the main limitation here.