4Ts Score for Heparin-Induced Thrombocytopenia

The 4Ts score predicts pretest risk for heparin-induced thrombocytopenia.

Feature Score
2 points 1 point 0 points
Thrombocytopenia >50% fall


platelet nadir 20-100 × 109/L

30%-50% fall


platelet nadir 10-19× 109/L

>30% fall


platelet nadir < 10×109/L

Timing of platelet count fall Clear onset on day 5-10, or =1 d if heparin exposure within past 30 d Consistent with day 5-10 fall, but not clear (eg, missing platelet counts); onset after day 10; or fall = 1 day if heparin exposure 30-100 days ago Platelet count fall =4 d without recent heparin exposure
Thrombosis or other sequelae New thrombosis (confirmed); skin necrosis; acute systemic reaction after IV UHF bolus Progressive or recurrent thrombosis; erythematous skin lesions; thrombosis suspected but not proven None
Other causes of thrombocytopenia None apparent Possible Definite

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