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. 2022 Apr 21;52(5):717–723. doi: 10.1111/imj.15783

Table 2.

Case definition criteria for VITT, UK expert haematology panel (EHP) and THANZ criteria

Type of VITT UK EHP 11 THANZ 12
Definite VITT All five of the following:
  • Onset of symptoms 5–30 days after vaccination against SARS‐CoV‐2 (or up to 42 days in those with isolated DVT or PE)

  • Presence of thrombosis

  • Thrombocytopenia (<150 ×109/L)

  • D‐dimer >4000 FEU

  • Positive anti‐PF4 antibodies on ELISA

  • Exposure to ChAdOx1 nCov‐19 (AstraZeneca) within 4–42 days of symptom onset

  • Thrombocytopenia (platelet count <150 ×109/L) or falling platelet count, AND elevated D‐dimer (>5 times the upper limit of normal) or reduced fibrinogen

  • Thrombosis: any DVT, PE or arterial thrombosis. Thrombosis in uncommon sites such as CVST and splanchnic vein thrombosis are strongly suggestive

  • Antibodies detected against PF4 and/or functional assay indicating patient derived plasma/serum induction of prothrombotic phenotype in healthy donor platelets

Probable VITT

D‐dimer level u >4000 FEU but one criteria not met (timing, thrombosis, thrombocytopenia or anti‐PF4 antibodies)

OR D‐dimer level unknown or 2000–4000 FEU and all other criteria met

Meets platelet count, D‐dimer (and/or fibrinogen) criteria, with thrombosis but PF4 antibody negative
Possible VITT D‐dimer level unknown or 2000–4000 FEU with one other criterion not met, or two other criteria not met Meets platelet count, D‐dimer (and/or fibrinogen) criteria but no thrombosis found
Unlikely VITT

Platelet count <150 ×109/L without thrombosis, with D‐dimer <2000 FEU

OR thrombosis with platelet count >150 ×109/L and D‐dimer <2000 FEU regardless of PF4 antibody result, and alternative diagnosis more likely

‘Less likely’ if platelet count >150 ×109/L but D‐dimer elevated or fibrinogen reduced with thrombosis

‘Much less likely’ if platelet count is stable and >150 ×109/L, D‐dimers are not elevated and fibrinogen is normal with thrombosis

Adapted from Pavord et al. 11 and Chen et al. 12

CVST, cerebral venous sinus; DVT, deep vein thrombosis; ELISA, enzyme‐linked immunosorbent assay; PE, pulmonary embolism; PF4, platelet factor‐4; VITT, vaccine‐induced thrombotic thrombocytopenia.