PF4 and Thrombocytopenia: The British Society of Haematology, guidance [15], recommends a definite diagnosis of VITT be made in the presence of all five criteria: (i) onset of symptoms 5–30 days post-COVID-19 vaccine (or up to 42 days if isolated DVT/PE), (ii) presence of thrombosis, (iii) thrombocytopenia (platelet count < 150 × 109/L), (iv) D dimer > 4000 mcg/L (FEU) and (v) positive anti-PF4 Antibody ELISA assay.