PF4 and Venous thrombosis: According to guidelines from the American Society of Hematology, a diagnosis of VITT should be made according to the following criteria: (1) COVID-19 vaccination 4 to 42 days prior to symptom onset; (2) thrombosis (evidence of venous or arterial thrombosis); (3) thrombocytopenia (platelet count below 150 × 109/L); (4) positive for anti-PF4 antibodies in immunoassays; and (5) significantly elevated D-dimer (exceeding 4 times the upper limit of normal) [28].