Method and apparatus for obtaining an absolute white blood cell subset count and white blood cell multipart differential

A method of optically screening and counting microscopic cells, comprising:

• providing a complete whole blood sample with an anticoagulating agent or a portion thereof including a plurality of cells and including at least one WBC population;
• combining at least a first portion of said cells with at least a first set of microspheres having at least a first reactant bound thereto specific to at least a first specific molecule which can exist on at least one type of cell to form a sample mixture, said first reactant being a CD4 specific molecule antibody specific to at least said first specific molecule which is a first cell antigen;
• combining said first portion of said cells with at least a second set of microspheres having at least a second CD14 antibody bound thereto specific to at least a second specific antigen which can exist on at least one type of cell, said second set of microspheres having a different optical characteristic from said first set of microspheres;
• deleting the RBC population from said sample prior to forming said sample mixture on a slide;
• forming a specific volume of said sample mixture on a slide;
• optically viewing at least some of said cells with a microscope to at least identify and count at least the presence of cells to which said first set of microspheres are bound including said cells to which said CD4 microspheres are bound and obtaining a CD4 absolute count and to at least identify the presence or absence of cells to which said second set of microspheres are bound;
• and
• relating said cell count to said specific volume to obtain an absolute CD4 cell count.