PF4 and COVID-19: Similarly, ADAMTS13 levels were reduced (p = 0.009) and the VWF/ADAMTS13 ratio was increased (p = 0.0004) in convalescent COVID-19 patients with dysregulated angiogenesis and immunothrombosis, while levels of PF4 (a putative protector of VWF) were also elevated (p = 0.0001) (55).