4Ts category | 2 points | 1 points | 0 points |
---|---|---|---|
Thrombocytopenia | Platelet count decrease >50 % and platelet nadir >20 × 109 L−1 | Platelet count decrease 30–50 % or platelet nadir 10–19 × 109 L−1 | Platelet count decrease <30 % or platelet nadir <10 × 109 L−1 |
Timing of the platelet count decrease | Clear onset days 5–10 or platelet decrease <1 day (prior heparin exposure within 30 days) | Consistent with the day 5–10 decrease, but not clear; onset after day 10, or decrease <1 day (prior heparin exposure 30–100 days ago) | Platelet count decrease <4 days without recent heparin exposure |
Thrombosis or other sequelae | New thrombosis (confirmed); skin necrosis; acute systemic reaction to the post-intravenous unfractionated heparin bolus | Progressive or recurrent thrombosis; non-necrotizing (erythematous) skin lesions; suspected thrombosis (not proven) | None |
Other causes of thrombocytopenia | None apparent | Possible | Definite |