An optical screening method and apparatus for identifying and counting cells expressing selected characteristics or properties. The cells are combined with one or more different sets of microspheres, each set having a reactant bound thereto which will bind to a specific molecule which can exist on one or more types of the cells. The cells and microspheres are formed in a known volume on a slide and optically viewed to identify and count the type of cells to which the different sets of microspheres do or do not bind. The cell count then is related to the known volume to provide an absolute cell count. A plurality of different sample portions can be utilized with different reactants to obtain a multipart WBC differential/absolute count. The different sets of microspheres are optically differentiated by having different optical characteristics, such as size, shape, color or combinations thereof.
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