TFPI and COVID-19: Several studies have demonstrated that severe COVID-19 is associated with increased circulating levels of such endothelial markers, including procoagulant von Willebrand factor (vWF) (15), plasminogen activator inhibitor (PAI-1) (16), vascular cell adhesion markers (17–19), and increased circulating antithrombotic endothelial surface proteins tissue factor pathway inhibitor (TFPI) (20) and thrombomodulin (21), which are cleaved off the endothelial surface during inflammation (22).