PF4 and Thrombocytopenia: Per the American Society of Hematology (32), which corresponds its classification of VITT with the Brighton Collaboration Criteria (33) and the UK Hematology Expert Group (34), VITT is classified by five criteria: (1) COVID-19 vaccine administered 4 to 42 days prior to symptom onset; (2) venous or arterial thrombosis (usually cerebral or abdominal); (3) thrombocytopenia (platelet count <1.50E+12/L); (4) dramatically elevated D-dimer (> 4 times the upper limit of normal); and (5) positive anti-PF4 antibody titers.