The UK Haematology Expert Group developed consensus diagnostic criteria for VITT
| Case definition criteria |
| Onset of symptoms 5-30 days after COVID-19 vaccine (or up to 42 days if isolated DVT/PE) |
| Presence of thrombosis |
| Thrombocytopenia (platelet count <150 × 109/L) |
| D-dimer >4000 μg/mL (FEU) |
| Positive anti-PF4 Abs ELISA |
| Definite VITT |
| Meets all 5 criteria |
| Probable |
| D-dimer >4000 FEU but one criterion not fulfilled (timing, thrombosis, thrombocytopenia, anti-PF4 Abs), or |
| D-dimer unknown or 2000-4000 FEU with all other criteria present |
| Possible |
| D-dimer unknown or 2000-4000 FEU with one other criterion not fulfilled, or |
| Two other criteria not fulfilled (timing, thrombosis, thrombocytopenia, anti-PF4 Abs) |
| Unlikely |
| 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 anti-PF4 Ab result, and/or |
| Case definition criteria |
| Onset of symptoms 5-30 days after COVID-19 vaccine (or up to 42 days if isolated DVT/PE) |
| Presence of thrombosis |
| Thrombocytopenia (platelet count <150 × 109/L) |
| D-dimer >4000 μg/mL (FEU) |
| Positive anti-PF4 Abs ELISA |
| Definite VITT |
| Meets all 5 criteria |
| Probable |
| D-dimer >4000 FEU but one criterion not fulfilled (timing, thrombosis, thrombocytopenia, anti-PF4 Abs), or |
| D-dimer unknown or 2000-4000 FEU with all other criteria present |
| Possible |
| D-dimer unknown or 2000-4000 FEU with one other criterion not fulfilled, or |
| Two other criteria not fulfilled (timing, thrombosis, thrombocytopenia, anti-PF4 Abs) |
| Unlikely |
| 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 anti-PF4 Ab result, and/or |
Reproduced from “Vaccine induced immune thrombocytopenia and thrombosis: summary of NICE guidance,” Pavord S, Hunt BJ, Horner D, Bewley S, Karpusheff J; Guideline Committee. BMJ. 375:n2195, © 2021, with permission from BMJ Publishing Group Ltd.84