Validation of flow cytometric detection of platelet microparticles and liposomes by atomic force microscopy

Background: Platelet microparticles (PMPs) are a promising prognostic marker for thrombotic disorders because of their release during platelet activation. The use of flow cytometry for the enumeration of PMPs in plasma has generated controversy due to their size, which is below the stated detection limits of conventional flow cytometry instruments. The potential impact of this is an underestimation of PMP counts. Objectives/Methods: To address this possibility, we used a combination of fluorescence‐activated cell sorting (FACS) and atomic force microscopy (AFM) to determine the size distribution of PMPs present in plasma from acute myocardial infarction (AMI) patients and normal volunteers, and PMPs generated by expired platelet concentrates and washed platelets treated with agonists such as thrombin and calcium ionophore (A23187). Results: According to AFM image analysis, there was no statistically significant difference in height or volume distributions in PMPs from thrombin‐activated, calcium ionophore‐activated, expired platelet concentrates and plasma from healthy volunteers and AMI patients. Based on volume, expired platelets released the greatest proportion of exosomes (