Heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) is a growing complication of a common medication used to prevent deep vein thrombosis (DVT) in hospitalized patients. The purpose of this article is to review the mechanism that causes paradoxical thrombus formation in HIT and ways to recognize this important complication with various testing modalities and to discuss the approaches to treatment once a diagnosis has been made. HIT is a clinical diagnosis that can be further supported by utilizing the "4 Ts": thrombocytopenia, timing of platelet count fall, thrombosis or other complications, and other causes for thrombocytopenia. Diagnosis of HIT can be established using an HIT antibody test. Once a drop in platelet count is observed in a patient, it is important to rule out HIT. When HIT is first suspected, it is important to discontinue all heparin products. The gold standard in diagnosing HIT is the 14C-serotonin release assay (14C-SRA) assay, which has high sensitivity and specificity but is technically demanding and more time consuming than other antibody-detecting immunoassays. Anticoagulation in HIT patients is essential due to the increased risk of thrombosis. Treatment consists of utilizing alternative, nonheparin anticoagulants like lepirudin, argatroban, bivalirudin, or fondaparinux (although fondaparinux is not formally approved by the US Food and Drug Administration for this condition). Each of these agents should be individually formulated based on the patient and the presence/absence of liver or renal failure. Treatment duration has yet to be determined. However, in patients requiring long-term anticoagulation (pulmonary embolism, DVT, stroke), the transition to warfarin can be made once the platelet count recovers and there has been at least 5 days of overlap with a nonheparin anticoagulant.