A guidebook on cytogram interpretation, written by Graham Gibbs and published recently, should prove very useful to anyone who uses a haematology analyser. Assessment of blood film morphology following an abnormal full blood count (FBC) is a traditional and fundamental aspect of diagnostic haematology. Nationally, review rates vary from below 5% to as much as 100% in certain specialist laboratories. However, as boundaries between different sections of pathology disappear and workload and skill-mix change, the level of morphology skill often varies among staff members.
Harnessing the graphical outputs of haematology analysers to assist with the identification of cellular abnormalities is not new, but its ability to support some of the changes faced by modern pathology services has caused a resurgence of interest in recent years. In many instances, these scattergrams (cytograms) have characteristic appearances across a wide range of pathological conditions. A process of pattern recognition can be used as a starting point for multidisciplinary staff and to help guide biomedical scientists towards appropriate confirmatory testing and/or the need for urgent clinical intervention. In addition, as these instruments analyse tens of thousands of cells, many more than human observers do, they can sometimes be more sensitive in detecting very small numbers of abnormal cells than light microscopy alone.
Modern analysers are extremely efficient in counting white cells, red cells and platelets accurately and provide mean values for all of the cells analysed (eg mean cell volume [MCV], mean cell haemoglobin [MCH] and mean cell haemoglobin concentration [MCHC] for red cells). However, by definition, these numerical assessments are averages of 20–30,000 cells. Cytogram inspection allows the observation of differences in the distribution of these cells that may suggest a preliminary diagnosis that numerical data alone may be neither sufficiently sensitive nor specific enough to detect.
White cells
The ADVIA 120/2120i haematology systems (Siemens Healthcare Diagnostics, Surrey, UK) are in use in many laboratories today, having evolved from the earlier Technicon H* series analysers and offer state-of-the-art cytograms using a combination of flow cytometry and myeloperoxidase (MPO) cytochemistry.
There are three main approaches for detecting white cell abnormalities using the cellular ‘imaging’ provided by the ADVIA, namely peroxidase activity and nuclear density analysis (PANDA), positional abnormalities, and the phenomenon of pseudobasophilia.
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