PF4 and deep vein thrombosis: Thrombosis, thrombocytopenia, and platelet‐activating antibodies to platelet factor 4–polyanion complexes were documented as part of an underlying illness known as “vaccine‐induced immune thrombotic thrombocytopenia” (VITT), or “thrombosis with thrombocytopenia syndrome” (TTS).9, 10, 11