Urine cytology by a filter imprint method.

The introduction of programmes to detect bladder cancer in people exposed to carcinogens and the increased interest in the value of urinary cytology as a diagnostic procedure have resulted in the need for a satisfactory method of preparing specimens. Ideally, the method must be simple to perform and reproducible, and result in a high degree of cellular clarity and minimal cellular distortion. Various methods have been used. Smears have been made from centrifuged deposits (Cowen, 1971). The problems encountered with this method have been loss of cells from the slide, partly overcome by using frosted glass slides or coating the slides with albumin, drying artefacts, and the difficulty of obtaining an adequately cellular preparation. Cytocentrifugation, where the cells are spun onto slides, has been introduced more recently, but recovery rates have been found to be poor, and there is also cellular distortion (Barrett and King, 1976). In many respects membrane filter techniques using polycarbonate or cellulose esters have been found to be superior and are generally regarded as preferable (Tyrkkb, 1972). These two materials differ in their physical, chemical, and optical properties and need to be treated differently (Gill, 1975). Both, however, have their disadvantages. The pore outlines of polycarbonate filters remain visible and are a distraction during microscopy. A method does exist for rendering them invisible, but it is technically exacting and can result in irrevocable damage to the preparation. Although this problem is not present with cellulose filters, the material itself and the mucus and bacterial or other debris, which tend to get trapped within the pores, absorb stain, obscuring the morphological detail of the exfoliated cells. We have modified the filtration technique by making an imprint onto a glass slide of the cells trapped on a membrane filter.