PLATELET DISORDERS
Normal platelet function and a platelet count greater than 100,000/cu mm in the peripheral blood are needed for normal primary hemostasis (Fig. 55-1). The platelet count represents the net balance between platelet production rate and the rate of loss or peripheral destruction of platelets. Since the bone marrow has the capacity to increase platelet production 8- to 10-fold, and platelets survive 8 to 10 days in the circulation, the platelet count can be maintained under most circumstances, even if losses or destruction are increased. Young platelets are more metabolically active and more hemostatically effective than older ones. Platelet adhesion, procoagulant activity, and aggregation and release of vasoactive substances must also be normal for hemostatic effectiveness. Impairment of one or several of these functions leads to a bleeding tendency characterized by mucosal and skin bleeding, purpura, and prolonged oozing of blood after trauma or surgery.