Role of red blood cells in haemostasis and thrombosis

In contrast to an obsolete notion that erythrocytes, or red blood cells ( RBC s), play a passive and minor role in haemostasis and thrombosis, over the past decades there has been increasing evidence that RBC s have biologically and clinically important functions in blood clotting and its disorders. This review summarizes the main mechanisms that underlie the involvement of RBC s in haemostasis and thrombosis in vivo , such as rheological effects on blood viscosity and platelet margination, aggregation and deformability of RBC s; direct adhesion and indirect biochemical interactions with endothelial cells and platelets. The ability of stored and pathologically altered RBC s to generate thrombin through exposure of phosphatidylserine has been emphasized. The procoagulant and prothrombotic potential of RBC ‐derived microparticles transfused with stored RBC s or formed in various pathological conditions associated with haemolysis has been described along with prothrombotic effects of free haemoglobin and haem. Binding of fibrinogen or fibrin to RBC s may influence their effects on fibrin network structure, clot mechanical properties and fibrinolytic resistance. Recent data on platelet‐driven clot contraction show that RBC s compressed by platelets pulling on fibrin form a tightly packed array of polyhedral erythrocytes, or polyhedrocytes, which comprises a nearly impermeable barrier important for haemostasis and wound healing. RBC s may perform dual roles, both helping to stem bleeding but at the same time contributing to thrombosis in a variety of ways.