Non-gynaecological cytopathology: the importance of preparation

Non-gynaecological cytology can be used widely to provide diagnoses in symptomatic patients or those at increased risk of disease. As the treatment of cancer has become targeted and personalised, the use of non-gynaecological cytology, together with ancillary techniques, has become more important. Cytology has the advantage over more invasive procedures as it cannot only be diagnostic but can also be used repeatedly to examine and monitor disease during treatment. Traditionally, non-gynaecological cytology samples have been prepared and prescreened by the staff practising gynaecological cytology, but the centralisation of many of these services, together with the transfer of staff, has left many departments without the required expertise. With the challenges these departments will now be facing, it is perhaps a good time to get back to basics and think about the principles of sample preparation and quality in non-gynaecological cytology.

                In some body sites, cells may naturally exfoliate and a sample can be collected easily; a good example of this is a voided urine. However, the collection of most samples will require intervention, which may be only minimally invasive but will still be uncomfortable for the patient and will require valuable clinic time. For this reason, we need to ensure that we get as much information as possible from each sample to be able to provide a comprehensive diagnosis, and preparation quality is crucial to this. The sample needs to be processed in an appropriate manner, optimally diluted and excess red blood cells need to be removed. It may sound obvious but samples should be prepared so that diagnostic material is clearly visible.

                There are many preparation methods available for non-gynaecological cytology, from direct spreads to semi- automated liquid-based techniques. All except direct spreads initially concentrate the cells and then employ techniques to produce a thin layer of cells. Semi-automated methods such as SurePath and ThinPrep have advantages over manual centrifugation methods as they remove the need for operator-dependent dilution, which is a critical step in creating a good-quality preparation. Many of the commercial non-gynaecological preservatives lyse red blood cells, removing the need for additional steps. A single layer of cells is achieved by diluting the deposit until it is just cloudy. Achieving this can be intimidating, but you cannot really over dilute a sample. If the worst happens you can always centrifuge it again and start over. If the deposit is not sufficiently dilute, the preparations will be over thick and cellular detail will be obscured. Table 1 show a simple dilution chart with suggested volumes of diluent to deposit size, which should result in a monolayer.