Development and refinement of a portable electronic device for haematocrit determination

A SMALL PORTABLE ELECTRONIC DEVICE, named a blood electrometer (BEM), was developed to measure packed cell volume, which can be related to haematocrit (Hct). The electronic circuitry is simple and constructed from standard components. Being battery powered, the device is suitable for bedside or field use (‘point-of-care-testing’) without specialized training. The effects of temperature, anticoagulants, lipid content, electrode type and different BEM electronic circuits on measurement accuracy were evaluated. A method for calibrating the instrument with a sodium chloride calibrator was also devised and evaluated for measurement accuracy. The response of the BEM to Hct is non-linear; a binomial regression function was used to fit the non-linear response to provide accurate Hct values from BEM readings over a wide range of measurements. The BEM response curve is sensitive to the anticoagulant type used, but specific binomial functions reduce error to between –3.1% and +3.3% Hct units. Lipids do not significantly affect BEM readings, even at high concentrations of 9.8 mmol/l. We conclude that the BEM can be relied on for acceptably accurate Hct measurements under a variety of conditions, and can be used for the indirect determination of packed cell volume.