Table 1.
4T score as studied by Lo et al[38]
| Points (0, 1, or 2 for each of 4 categories: maximum possible score = 8) | |||
| 2 | 1 | 0 | |
| Thrombocytopenia | > 50% fall or platelet nadir ≥ 20 × 109/L | 30%-50% fall or platelet count 10-19 × 109/L | Fall < 30% or platelet nadir < 10 × 109/L |
| Timing of fall in platelet count | Clear onset between day 5-101; or less than 1 d (if history of heparin exposure within 30 d) | Consistent with d 5-10 fall, but not clear (e.g., missing platelet counts) or onset of thrombocytopenia after d10 or fall ≤ 1 d (prior heparin exposure 30-100 d ago) | Platelet count fall < 4 d without recent heparin exposure |
| Thrombosis or other sequelae (e.g., Skin lesions) | New thrombosis; skin necrosis; acute systemic reaction post unfractionated heparin bolus | Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis not yet proven | None |
| Other cause of thrombocytopenia | None apparent | Possible other cause is evident | Definite |
| 4T score: 6-8 = High; 4-5 = Intermediate; 0-3 = Low | |||
1
5-10 d after exposure to heparin or low molecular weight heparin.