Standardization of extracellular vesicle measurements by flow cytometry

From 2014 to 2016, we participated in a project to standardize concentration measurements of extracellular vesicles by flow cytometry through vesicle diameter approximation.


Together with the International Society on Thrombosis and Haemostasis (ISTH), the European Metrology Research Programme METVES, and the Vesicle Observation Center of the Academic Medical Center in Amsterdam, Exometry initiated a project to standardize measurements on extracellular vesicles (EV) by flow cytometry.

Flow cytometers can count and identify individual EV at a rate of thousands per second. Because flow cytometers differ in optical configuration, different flow cytometers obtain different EV concentrations for the same sample. Moreover, because flow cytometers provide data in arbitrary units, data on EV cannot be compared between laboratories. The goal of this standardization study is to improve the reproducibility of the measured concentration of EV by different commercially available flow cytometers.

To standardize EV measurements, flow cytometers were calibrated using traceable reference materials and light scattering theory. The used reference materials have been extensively characterized by European metrology institutes in the METVES project. Exometry has developed easy-to-use software to automatically recognize the reference materials, obtain the optical configuration of the flow cytometer, and set an EV size gate in nanometers. This size gate is calculated with Mie theory and takes into account the optical configuration of the flow cytometer and the refractive index of EV. The size gate ensures that each flow cytometer will determine the concentration of EV in the same size range.

World map of collaborators in the ISTH / METVES standardization project

This study is sponsored by the ISTH and involves 31 clinical laboratories worldwide. The study runs from 2014 to 2016.