Table 2.

4Ts pretest clinical score of HIT [23].

	2 Points	1 Point	0 Point
Thrombocytopenia	Platelet count fall > 50% and platelet nadir ≥ 20 G/L	Platelet count fall 30%–50% or platelet nadir 10–19 G/L	Platelet count fall < 30% or platelet nadir < 10 G/L
Timing of platelet count fall	Clear onset between days 5–10; or platelet fall ≤ 1 day with prior heparin exposure within 30 days	Consistent with days 5–10 fall, but not clear; onset after day 10; or fall ≤ 1 day with prior heparin exposure between 30–100 days ago	Platelet count fall < 4 days without recent exposure
Thrombosis or other sequelae	New thrombosis (confirmed); skin necrosis; acute systemic reaction post IV UFH bolus	Progressive or recurrent thrombosis; non-necrotizing (erythematous) skin lesions; suspected thrombosis	None
oTher causes for thrombocytopenia	None apparent	Possible	Definite

IV: intravenous; UFH: unfractionated heparin.