Heparin induced thrombocytopenia in critically ill: Diagnostic dilemmas and management conundrums

Table 1 4T score as studied by Lo et al[38]

Points (0, 1, or 2 for each of 4 categories: maximum possible score = 8)
	2	1	0
Thrombocytopenia	> 50% fall or platelet nadir ≥ 20 × 109/L	30%-50% fall or platelet count 10-19 × 109/L	Fall < 30% or platelet nadir < 10 × 109/L
Timing of fall in platelet count	Clear onset between day 5-101; or less than 1 d (if history of heparin exposure within 30 d)	Consistent with d 5-10 fall, but not clear (e.g., missing platelet counts) or onset of thrombocytopenia after d10 or fall ≤ 1 d (prior heparin exposure 30-100 d ago)	Platelet count fall < 4 d without recent heparin exposure
Thrombosis or other sequelae (e.g., Skin lesions)	New thrombosis; skin necrosis; acute systemic reaction post unfractionated heparin bolus	Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis not yet proven	None
Other cause of thrombocytopenia	None apparent	Possible other cause is evident	Definite
4T score: 6-8 = High; 4-5 = Intermediate; 0-3 = Low

¹5-10 d after exposure to heparin or low molecular weight heparin.