PF4 and COVID-19: The diagnostic criteria for definite VITT-associated CVT are post-vaccine CVT (between 4 and 28 days after COVID-19 vaccination), thrombocytopenia (lowest recorded platelet count <150 × 109 per L or documented platelet count), anti-platelet factor four (PF4) antibodies (detected on ELISA or functional assay) [45,46,47].