Heparin-induced thrombocytopenia.
Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug effect that is characterized by platelet activation, hypercoagulability, and a resulting increased risk for thrombosis, both venous and arterial. This disorder is autoimmune-like, because the target antigen is a multimolecular complex of the "self" protein, platelet factor 4, and heparin. HIT usually begins 5 to 10 days after starting heparin, especially when administered intra- or perioperatively, although a rapid onset of thrombocytopenia can occur if heparin is given to a patient with circulating HIT antibodies that resulted from a recent heparin exposure. The clinical diagnosis is supported if heparin-dependent, platelet-activating antibodies are detectable. Treatment includes cessation of heparin and use of an alternative non-heparin anticoagulant, such as danaparoid, lepirudin, or argatroban. Warfarin must be avoided or postponed, as the acute phase of HIT poses a high risk for coumarin necrosis, particularly limb loss due to venous limb gangrene.
Warkentin
Theodore E
TE
Department of Pathology and Molecular Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada. twarken@mcmaster.ca
D000906:Antibodies / Q000097:blood; D000925:Anticoagulants / Q000627:therapeutic use; D006493:Heparin / Q000009:adverse effects* / Q000276:immunology; D006801:Humans; D015539:Platelet Activation; D010978:Platelet Factor 4 / Q000276:immunology; D013921:Thrombocytopenia / Q000139:chemically induced*
D000906:Antibodies; D000925:Anticoagulants; D010978:Platelet Factor 4; D006493:Heparin