PF4 and pulmonary embolism: Intrinsic hypercoagulability and activating procoagulant factors, such as the tissue factor (TF), platelet factor 4 (PF4), and plasminogen activator inhibitor type 1 (PAI-1) often cause deep vein thrombosis, pulmonary embolism, disseminated intravascular coagulation, portal vein thrombosis, or arterial thromboembolism [40].