Table 3.

4 T's score for heparin-induced thrombocytopenia

Category	2 points	1 point	0 point
Thrombocytopaenia	>50% fall or nadir ≥20 ×109/l	30–50% fall or nadir 10–19×109/l	<30% fall or nadir < 10 ×109/l
Timing of the decrease in platelet count	Day 5 to 10 or ≤day 1 with recent heparin (past 30 days)	>Day 10 or timing unclear or < day 1 if heparin exposure within 30–100 days	<Day 4 with no recent heparin use
Thrombosis or other sequelae	Proven thrombosis, skin necrosis, or acute systemic reaction after heparin bolus	Progressive, recurrent, or silent thrombosis; erythematous skin lesions	None
Other causes of thrombocytopenia	None evident	Possible	Definitive