A methodology and a mathematical relationship have been developed that allow quantitation of the expression levels of cellular surface antigens, in terms of antibody binding capacities (ABC). This methodology uses immunomagnetically labeled cells and calibration microbeads combined with cell tracking velocimetry (CTV) technology to measure magnetophoretic mobilities corresponding to cellular ABC. The mobility measurements were accomplished by microscopically recording and calculating the velocity of immunomagnetically labeled QSC microbeads and cells in a nearly constant magnetic energy gradient.