Quantitative Flow Cytometry—Medical Applications with a Focus on Blood Platelets

Flow cytometry, measuring light signals, can be used as a quantitative tool to appreciate the numbers of cell-surface molecules targeted with monoclonal antibodies, among other applications. This has been extensively used for blood cells and especially platelets. This review describes how techniques have evolved over time since the first developments of quantitative flow cytometry at the end of the 20th century. Technological issues are first described, applicable to all types of cells/molecules and largely relying on calibration beads with direct or, preferably, indirect immunofluorescence. The platelet field is then addressed with specific tools devoted to surface antigen quantitation. The array of commercially available kits is provided with their specificity. A panorama of platelet antigens quantified that can be used in the diagnosis workout of platelet disorders is then provided, accompanied by a reminder of the impressive stability of marker expression in normal individuals. Variations are then considered in the light of aging or genetic polymorphisms. Finally, the upcoming use of platelet antigen quantification as a monitoring tool for emerging targeted therapies is evoked. All in all, this review provides a comprehensive story of the evolution of the still too marginally used cell antigen quantification.