Coagulation Disorders

Haemostasis has two linked stages. Primary haemostasis uses platelets and von Willebrand factor (VWF) to form an initial plug at the site of vessel injury. Secondary haemostasis 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-haemostasis defect causes mucosal bleeding, easy bruising, epistaxis, heavy menstrual bleeding, and prolonged bleeding from superficial wounds. A secondary-haemostasis defect causes deeper bleeding: haemarthrosis, muscle haematomas, 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 stabilises 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. HIT produces platelet activation and thrombin generation despite a falling platelet count. DIC activates coagulation throughout the circulation, creating microvascular thrombi while consuming platelets and clotting factors. TTP produces platelet-rich...