Previous investigators have established that in the absence of endothelial damage, erythrocytes and endothelial cells do not present sufficient amounts of phosphatidylserine on the cell surface to bind factors X and Xa In vitro, it has been shown that HS cells have accelerated lipid loss , which may provide increased substrate for procoagulant activation. Furthermore, when platelets are activated their phosphatidylserine content increases from 13% to approximately 30%. Platelet activation causes the transfer of anionic phospholipid (primarily phosphatidylserine) from the inner to the outer leaflet of the membrane, accelerating the coagulation process