Enumeration of Absolute Cell Counts Using Immunophenotypic Techniques

Absolute counting of cells or cell subsets has a number of significant clinical applications: monitoring the disease status of HIV‐infected patients, enumerating residual white blood cells in leukoreduced blood products, and assessing immunodeficiency in a variety of situations. The single‐platform method (flow cytometry alone) has emerged as the method of choice for absolute cell enumeration. This technology counts only the cells of interest in a precisely determined blood volume. Exact cell identification is accomplished by a logical electronic gating algorithm capable of identifying lineage‐specific immunofluorescent markers. Exclusion of unwanted cells is automatic. This extensive and detailed unit presents protocols for both volumetric and flow‐rate determination of residual white blood cells and of leukocyte subsets.