Table 2.
The 4 T's score [32]
| Score | |||
|---|---|---|---|
| 4 T Category | 2 | 1 | 0 |
| Thrombocytopenia | Platelet count decrease > 50% or platelet nadir ≥ 20 × 109/L | Platelet count decrease 30-50% or platelet nadir 10-19 × 109/L | Platelet count decrease < 30% or platelet nadir < 10 × 109/L |
| Time to platelet count decrease* | Clear onset between days 5-10 or platelet count decrease ≤ 1 day (prior heparin exposure within 100 days) | Consistent with decrease between days 5-10, but not clear (e.g., missing platelet counts); onset after day 10 | Platelet count decrease < 4 days without recent exposure |
| Thrombosis or other sequelae | New thrombosis (confirmed); skin necrosis; acute systemic reaction postintravenous heparin | Progressive or recurrent thrombosis; non-necrotizing (erythematous) skin lesions; suspected thrombosis (not proven) | None |
| Other causes of thrombocytopenia | None apparent | Possible | Definite |
*First day immunizing heparin exposure considered day zero; the day the platelet count begins to decrease is considered the day of onset of thrombocytopenia.