<prompt> Platelet function tested byBleeding timeProthrombin timeClot retraction testThrombin time  <response>: A Bleeding time Most important screening tests of the primary hemostatic system are Bleeding time a sensitive measure of platelet function, and a platelet count. Latter correlates well with the propensity to bleed. The normal platelet count is 150,000 to 450,000mL of blood. As long as the count is 100,000mL, patients are usually asymptomatic and the bleeding time remains normal. Platelet counts of 50,000 to 100,000mL cause mild prolongation of the bleeding time; bleeding occurs only from severe trauma or other stress. Patients with platelet counts 50,000pL have easy bruising, manifested by skin purpura after minor trauma and bleeding after mucous membrane surgery. Patients with a platelet count 20,000pL have an appreciable incidence of spontaneous bleeding, usually have petechiae, and may have intracranial or other spontaneous internal bleeding 