Spurious elevation of automated leukocyte counts induced by Fluosol DA 20%

During studies with Fluosol DA 20% (FDA) in rats, an artifactual leukocytosis was observed when an impedance type electronic cell counter was used. The effect was found to be directly related to the duration of the interval between addition of an erythrocyte lysing fluid and counting, observed up to 11 d after transfusion with FDA, blood cell associated, reproducible in vitro, FDA concentration dependent, temperature dependent, and present when human blood was used instead of rat blood. Microscopically, the effect appears to be the result of agglutination of lysed erythrocyte membranes due to the interaction of erythrocytes, the emulsion component of FDA, and the quaternary ammonium salt component of the lysing fluid. These data suggest that FDA causes subtle changes in erythrocytes and raises the possibility that other cells may be similarly affected.