The 4Ts score for estimating the pretest probability of heparin-induced thrombocytopenia
| . | Points* . | ||
|---|---|---|---|
| . | 2 . | 1 . | 0 . |
| Thrombocytopenia (acute) | >50% platelet count fall to nadir ≥20 × 109/L | 30% to 50% platelet count fall to nadir 10-19 × 109/L | <30% platelet count fall to nadir ≤10 × 109/L |
| Timing of fall in platelet count or other sequelae | Onset days 5-10 or <1 d (if heparin exposure within 30 d) | After day 10, or timing unclear, or before day 1 with recent heparin 31-100 d | Platelet count fall before day 4 (without recent heparin exposure) |
| Thrombosis or other sequelae | New thrombosis; skin necrosis; post–heparin bolus acute systemic reaction | Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis, not confirmed | None |
| Other cause of thrombocytopenia | No other cause of platelet count fall is evident | Possible other cause is evident | Definite other cause is present |
| . | Points* . | ||
|---|---|---|---|
| . | 2 . | 1 . | 0 . |
| Thrombocytopenia (acute) | >50% platelet count fall to nadir ≥20 × 109/L | 30% to 50% platelet count fall to nadir 10-19 × 109/L | <30% platelet count fall to nadir ≤10 × 109/L |
| Timing of fall in platelet count or other sequelae | Onset days 5-10 or <1 d (if heparin exposure within 30 d) | After day 10, or timing unclear, or before day 1 with recent heparin 31-100 d | Platelet count fall before day 4 (without recent heparin exposure) |
| Thrombosis or other sequelae | New thrombosis; skin necrosis; post–heparin bolus acute systemic reaction | Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis, not confirmed | None |
| Other cause of thrombocytopenia | No other cause of platelet count fall is evident | Possible other cause is evident | Definite other cause is present |
Pretest probability score: 6-8 = high; 4-5 = intermediate; 0-3 = low.
Score of 0, 1, or 2 for each of the four parameters (maximum points = 8).