Heparin-induced thrombocytopenia: diagnosis and management.

Heparin is the predominant anticoagulant used in cardiac and vascular surgery. Heparin-induced thrombocytopenia (HIT) is one of the most serious and life-threatening adverse drug reactions associated with heparin use. In addition to the development of thrombocytopenia, HIT is associated with a high risk (40-50%) of thrombotic complications. The pathophysiology of HIT is now well understood and results from the formation of platelet-activating antibodies against the heparin-platelet factor 4 complex (H-PF4) on the platelet surface. The risk of HIT varies significantly depending on the type of heparin (unfractionated heparin greater than low-molecular-weight heparin), duration of heparin use, and patient population (surgery greater than medical). Readily available serologic assays for serum antibodies against H-PF4 allow for rapid confirmation of a clinical diagnosis of HIT. Owing to the high risk of thrombosis associated with HIT, antithrombotic therapy with direct thrombin inhibitors (lepirudin or argatroban) should be started when serologic assays confirm clinical suspicion.