PF4 and deep vein thrombosis: Platelet factor 4 (PF4) disorders represent a range of immune‐mediated thrombogenic conditions which include heparin‐induced thrombocytopenia (HIT), comprising classic HIT (cHIT), autoimmune HIT (aHIT), delayed onset HIT, persisting (refractory) HIT, heparin ‘flush’ HIT and spontaneous HIT and vaccine‐induced immune thrombocytopenia and thrombosis (VITT)/VITT‐like syndromes.