Consensus report on markers to distinguish procoagulant platelets from apoptotic platelets: communication from the Scientific and Standardization Committee of the ISTH

Background: Procoagulant platelets are a subpopulation of highly activated platelets that promote coagulation through surface-exposed, negatively charged phospholipids, especially phosphatidylserine. Procoagulant platelets are important for clot stabilization during hemostasis, and an increased number of these platelets is associated with thrombotic risk. There is a need for harmonization in this area since many of the markers and methods used to assess procoagulant platelets are not specific when used in isolation but are also associated with platelet apoptosis. Objectives: We initiated this project to identify a minimum set of markers and/or methods that can detect and distinguish procoagulant platelets from apoptotic platelets. Methods: The study design involved a primary panel with 27 international experts who participated in an online survey and moderated virtual focus group meetings. Primary and secondary panel members were then invited to provide input on themes and statements generated from the focus groups. Results: This led to a recommendation to use flow cytometry and a combination of the following 3 surface markers to differentiate procoagulant platelets from apoptotic platelets: P-selectin (CD62P), phosphatidylserine (recognized by annexin V), and the platelet-specific receptor GPIX (CD42a) or α_IIb integrin (CD41, GPIIb). Conclusion: Procoagulant platelets are expected to be positive for all 3 markers, while apoptotic platelets are positive for annexin V and the platelet-specific surface receptor(s) but negative for P-selectin.