PF4 and Venous thrombosis: For a definite VITT diagnosis, a patient should meet all five of the following criteria: (1) the onset of symptoms 5–30 days after vaccination against SARS-CoV-2 (or less than 42 days in patients with isolated deep-vein thrombosis or pulmonary embolism), (2) the presence of thrombosis, (3) thrombocytopenia (PLT < 150,000 per cubic millimeter), (4) D-dimer levels of greater than 4000 FEU, and (5) positive anti-PF4 antibodies from ELISA.