Surrogate materials for calibration and control: the use of latex particles as calibrants for red cell volume measurements.

Latex particles, including BCR Certified Reference Material CRM 166a, have important applications for checking linearity and for calibrating aperture-impedance instruments used to determine red-cell volumes. Studies performed on Coulter Counters, e.g. the ZBi/C1000, ZM/C256 and Model S Plus IV, using a series of three different mono-sized latex particles have shown linearity but non-zero intercepts. This emphasizes the importance of calibrating instruments at more than one point. Latex particles also have an important role in calibration of red-cell volume measurements provided that a relative latex: red-cell shape factor has been assigned when the instrument is calibrated with fresh blood. Such relative shape factors are independent of latex particle size but need to be specific for instrument type and probably also for the orifice and diluent to be used. Nevertheless latex calibrants can serve an important role in standardizing red-cell volume measurements.