Method of simultaneously counting blood cells

Claim 1

An analytical method for counting the quantity of blood cells suspended in a predetermined quantity of fluid comprising a blood fraction comprising the steps of preparing said fluid for simultaneously counting the overall quantity of leucocytes suspended in said fluid, said preparing step comprising the steps of delivering a predetermined volume of whole blood to a calibrated separation tube, adding a predetermined volume of high molecular weight polysaccharide in physiological saline, mixing said whole blood and said polysaccharide-physiological saline volumes and letting said mixture stand to form an erythrocyte layer and a plasma layer above said erythrocyte layer, waiting until said layer of erythrocytes reaches a predetermined volume level in said tube and siphoning off said plasma layer to provide a predetermined volume of plasma, said siphoned plasma being an intermediary preparation, suspending said siphoned plasma in a reagent capable of lysing any residual erythrocytes and platelets to form a dilute final sediment, illuminating said dilute final sediment with a white light along an optical axis so as to illuminate substantially all of said suspended leucocytes substantially simultaneously; filtering the light directly transmitted through said dilute final sediment at an optical wavelength which passes light which has not been absorbed by said leucocytes, and providing a simultaneous count indication of said overall quantity in response to said filtered light.