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

## TL;DR

This review explains how quantitative flow cytometry has evolved to measure cell-surface molecules, especially on blood platelets, and its medical applications.

## Contribution

The paper provides a comprehensive overview of the evolution and current state of quantitative flow cytometry in platelet research and diagnostics.

## Key findings

- Quantitative flow cytometry has advanced to measure platelet surface antigens with calibration beads and immunofluorescence.
- Commercial kits for platelet antigen quantitation are available and can aid in diagnosing platelet disorders.
- Platelet antigen quantification is emerging as a tool for monitoring targeted therapies.

## Abstract

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.