PF4 and Thrombocytopenia: Additionally, the absence of positive results for anti-PF4/H and/or platelet functional tests in patients without thrombocytopenia but with thrombotic event within 1 month after COVID-19 vaccination confirm that VITT should be suspected only in patients who meet the VITT suspicion criteria as defined by the ISTH [15], thrombocytopenia being a major criterion for VITT suspicion and others PF4-related thrombotic disorders.