PF4 and deep vein thrombosis: Unlike other anti-platelet factor 4 (PF4) antibody-mediated disorders, such as heparin-induced thrombocytopenia (HIT), VITT arises with the development of platelet-activating anti-PF4 antibodies 4–42 days post-vaccination, typically featuring thrombocytopenia and thrombosis at unusual sites.