PF4 and Thrombocytopenia: Due to the occurrence of thrombocytopenia with extensive venous thrombosis, VITT was suspected, and an ELISA test for anti-platelet factor 4 (PF4) antibody was performed using the Lifecodes® PF4 IgG ELISA assay (Immucor, GTI Diagnostics, Waukesha, WI, USA.