Pathophysiology
Clinical meaning
Disseminated intravascular coagulation (DIC) involves systemic activation of coagulation triggered by tissue factor release (sepsis, trauma, malignancy, obstetric emergencies). Widespread microvascular thrombosis consumes platelets, fibrinogen, and clotting factors while simultaneously activating fibrinolysis, producing the paradox of simultaneous thrombosis AND bleeding. Heparin-induced thrombocytopenia (HIT) type II is an immune-mediated prothrombotic disorder: heparin binds platelet factor 4 (PF4), creating a neoantigen; IgG antibodies against heparin-PF4 complexes activate platelets via FcγRIIa receptors, causing intense platelet activation, aggregation, and thrombin generation. Despite thrombocytopenia, the predominant risk is THROMBOSIS (white clot syndrome), not bleeding.