Chapter 7 reviews physical and historical information that might suggest disruption in coagulation. The basic laboratory evaluation includes platelet count, bleeding time, prothrombin time (PT), partial thromboplastin time (PTT), and thrombin time. The minimal number of normally functioning platelets to prevent surgical bleeding is 50,000/mm3. It is important to note that both the PT and PTT require about a 60% to 80% loss of coagulation activity before becoming abnormal, but patients with smaller decreases in function can still have significant surgical bleeding. Therefore the history is still very important. Thromboelastography measures the combined function of platelets and coagulation factors.
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