PF4 and deep vein thrombosis: Refractory heparin-induced thrombocytopenia with thrombosis (HITT) is a rarely reported manifestation where the immunoglobulin G (IgG) antibodies against endogenous platelet factor 4 (PF4) in complex with heparin and resultant thrombocytopenia persist beyond the expected time to resolution (~4-10 days) after initiation of conventional therapy.