Coagulation Disorders

Hemostasis has two linked stages. Primary hemostasis uses platelets and von Willebrand factor (VWF) to form an initial plug at the site of vessel injury. Secondary hemostasis reinforces that plug with fibrin generated by the coagulation cascade. Fibrinolysis then removes the clot when repair is established. The clinical pattern often reveals which stage is failing. A primary-hemostasis defect causes mucosal bleeding, easy bruising, epistaxis, heavy menstrual bleeding, and prolonged bleeding from superficial wounds. A secondary-hemostasis defect causes deeper bleeding: hemarthrosis, muscle hematomas, retroperitoneal bleeding, or delayed bleeding after surgery. The patterns can overlap, particularly when a VWF disorder also lowers factor VIII. VWF is the bridge between injured subendothelium and platelet glycoprotein receptors. It also carries and stabilizes factor VIII in circulation. Too little VWF, or VWF that functions abnormally, therefore weakens platelet adhesion and may reduce factor VIII activity at the same time. The opposite problem is uncontrolled coagulation. Heparin-induced thrombocytopenia (HIT) produces platelet activation and thrombin generation despite a falling platelet count. Disseminated intravascular coagulation (DIC) activates coagulation throughout the circulation, creating microvascular thrombi while consuming platelets and...