Chapter 24 Heparin-Induced Thrombocytopenia

Heparin (HP)-induced thrombocytopenia (HIT) is an unusual immune-mediated adverse drug reaction with the central paradox being its strong association with thrombosis, despite the role of an anticoagulant (heparin) in causing a fall in platelet count. Platelet factor 4 (PF4) bound to endothelial surface heparan sulfate (HS) can be recognized by HIT antibodies, potentially causing endothelial cell activation, with procoagulant consequences. HP-induced skin lesions occur at HP injection sites in about 10% of patients forming anti-PF4/HP antibodies. These range from erythematous plaques to skin necrosis. Thrombocytopenia is common in hospitalized patients, and thrombocytopenia that occurs in a patient receiving HP has numerous potential explanations beside HIT. Certain disorders strongly resemble HIT on clinical grounds. If HIT is strongly suspected, all exposure to HP, including “flush” solutions and HP-coated catheters should be immediately discontinued, if possible. The duration of anticoagulation therapy primarily depends on the presence of any thrombosis. Vitamin K antagonists (VKAs), such as warfarin, are currently the most commonly used agents for prolonged anticoagulation, targeting an INR value around 2.0–3.0.