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Instability of reference materials may cause problems in interpreting results for assurance of quality in haemocytometry. The stability with time for a certain preserved blood specimen is also highly dependent on the principle of measurement.In this paper some effects of ageing on red cell populations in commercially available (Ortho) Blood Controls are evaluated. Red blood cell size histograms become narrower while mean corpuscular volumes obviously decrease with time when measurements are based on light scattering intensity.In contrast, monodisperse polystyrene spheres of different sizes show perfect stability at storage. Such artificially prepared controls should be applied to achieve optimal setting and calibration of haematology analysers.

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Characteristics with respect to light scattering intensity (LSI) were measured on latex spheres and on sphered and unsphered red blood cells (RBC). From the discrepancies in LSI signals from polymer spheres and RBCs it is obvious that latices cannot be used for absolute calibration of RBC sizes. Sphering of RBCs did not give rise to a closer resemblance. Monodisperse latex spheres produce extremely narrow size distribution histograms. Regarding these sharp peaks and the long-term stability, polymer spheres offer definite advantages if compared with blood controls to which preservatives were added. A shift from the RBC size distribution histogram, caused by gradually developing instrument drift, can be easily detected and corrected at an early stage.