Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an acquired hemostasis disorder due to an immune response to the presence of platelet factor 4 (PF4)-heparin complexes. HIT is characterized by thrombocytopenia, which may be associated with severe thrombosis, developed in association with heparin treatment or exposure. HIT is caused by activation of platelets by PF4-heparin-IgG immune complexes. The diagnosis of HIT is based on clinical criteria confirmed by specific laboratory tests to identify anti-PF4 antibodies capable of activating platelets in the presence of heparin. The aim of this chapter is to outline the clinical and laboratory data used for the diagnosis of HIT.