Pathophysiology, epidemiology, diagnosis and treatment of heparin-induced thrombocytopenia (HIT)

Due to the widespread use of unfractionated (UFH) and low molecular weight heparins (LWH) for prophylaxis and treatment of thrombosis, heparin-induced thrombocytopenia is considered to be the most frequent (and potentially the most devastating) drug-induced thrombocytopenia. Induced by an immune response, excessive activation of platelets and endothelium cells causes massive thrombin generation and, as a result, life-threatening venous and arterial thrombotic vessel occlusion. The rate of mortality and amputation in HIT II is estimated to be 30% and 20%, respectively. The clinical course of HIT II depends highly on early therapeutic intervention consisting of immediate interruption of heparin application and, most important, of compatible thrombin inhibition. All measures implying a potentially procoagulant risk such as begin of oral anticoagulation or platelet substitution may result in disastrous side effects.