The in Vivo Evaluation of the Hemostatic Function of Stored Human Platelets

The assessment of the hemostatic function of stored human platelets is difficult to assess in human subjects. The use of thrombocytopenic rabbits treated with ethyl palmitate to produce reticuloendothelial blockade, has made it possible to study the hemostatic function of human platelets in vivo. The assessment of hemostatic function has been made using both a jugular bleeding time technique and an ear bleeding time technique, and in both, a close correlation between bleeding time and platelet count has been established. Using both methods, both fresh and human platelets stored for 72 hours at 22°C correct the bleeding time of thrombocytopenic animals to levels appropriate to the platelet count achieved. Platelets stored at 4°C using standard methods of preparation and storage were ineffective hemostatically after 24 hours storage. Platelets prepared and stored at 4°C at a pH of 6.4 were hemostatically effective in thrombocytopenic rabbits for as long as 10 days of storage. No correlation, however, was noted between the hemostatic effect of stored platelets and in vitro tests of platelet function. Similarly, the intravenous infusion of ADP and collagen produced similar falls in platelet count for both hemostatically effective and non-effective platelets. These studies provide further evidence for the limitations of in vitro tests of platelet function for the assessment of the potential in vivo function of stored human platelets. Furthermore, these findings raise the possibility for the prolongued liquid storage of human platelets at conditions which minimize bacterial contamination, yet maintain hemostatic efficacy.