Which statement about the clinical presentation of heparin-induced thrombocytopenia (HIT) is most likely true?
Heparin-induced thrombocytopenia (HIT) is caused by antibody-mediated platelet aggregation after exposure to heparin. Heparin is known to cause the expression of several different glycoproteins on the platelet surface, including platelet factor 4 (PF4). It also causes release of PF4 from vascular endothelium. The heparin-PF4 complex forms the antigen responsible for the immune response. Antibodies bind to this complex on the platelet surface and activate the platelet via the Fcy II receptor. Aggregation of activated platelets follows. Severe and even fatal vascular thrombosis can occur. This is termed heparin-induced thrombocytopenia with thrombosis (HITT).
The classically described finding in HIT is a decrease in platelet count to less than 100,000/µL or to less than 50 percent of the baseline platelet count after exposure to heparin. Typically, the decrease in platelet count occurs several days after heparin exposure,...
