| 4T's |
2 points |
1 point |
0 point |
| Thrombocytopenia |
Platelet count fall >50% and platelet nadir ≥20* |
Platelet count fall 30–50% or platelet nadir 10–19 |
Platelet count fall <30% or platelet nadir <10 |
| Timing of platelet count fall |
Clear onset between days 5–10 or platelet fall ≤1day (prior heparin exposure within 30days)† |
Consistent with days 5–10 fall, but not clear (e.g. missing platelet counts); onset after day 10‡; or fall ≤1day (prior heparin exposure 30–100 days ago) |
Platelet count fall <4days without recent exposure |
| Thrombosis or other sequelae |
New thrombosis (confirmed); skin necrosis§; acute systemic reaction postintravenous unfractionated heparin (UFH) bolus |
Progressive or recurrent thrombosis¶; Non-necrotizing (erythematous) skin lesions§; Suspected thrombosis (not proven)** |
None |
| Other causes for thrombocytopenia |
None apparent |
Possible†† |
Definite†† |
Low probability: 0-3