Heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated reaction caused by exposure to heparin that can lead to devastating thrombotic complications. HIT usually occurs 5 to 10 days after exposure to heparin but can happen more rapidly to patients who are reexposed to heparin within 100 days. The hallmark of this disorder is a sudden drop in platelet count of greater than 50%. Once HIT is suspected the heparin must be immediately discontinued and an anticoagulant (direct thrombin inhibitor or heparinoid) started. For patients presenting for cardiac surgery and cardiopulmonary bypass that have a history of HIT and positive antibodies a direct thrombin inhibitor such as lepirudin, argatroban or bivalirudin must be used in lieu of heparin.