Outcome of postoperative critically ill patients with heparin-induced thrombocytopenia: an observational retrospective case-control study

Table 1 Pretest scoring system for HIT: the 4 Ts

4 Ts	2 points	1 point	0 points
Thrombocytopenia	Platelet count >50% and platelet nadir = 20*	Platelet count decrease 30% to 50% or platelet nadir 10 to 19	Platelet count decrease < 30% or platelet nadir < 10
Timing of platelet count decrease	Clear onset between days 5 and 10 or decrease = 1 day (prior heparin exposure within 30 days)	Consistent with decrease between days 5 and 10, but not clear (for example, missing platelet counts); onset after day 10; or decrease = 1 day (prior heparin exposure 30 to 100 days before)	Platelet count decrease < 4 days without recent exposure
Thrombosis or other sequelae	New thrombosis (confirmed); skin necrosis; acute systemic reaction after intravenous unfractionated heparin bolus	Progressive or recurrent thrombosis; non-necrotizing (erythematous) skin lesions; suspected thrombosis (not proven)**	None
Other causes for thrombocytopenia	None apparent	Possible++	Definite++

The clinical probability scores are high (6 to 8 points), intermediate (4 to 5 points), and low (0 to 3 points) [18]. HIT, heparin-induced thrombocytopenia.* Platelet count fall >50% or nadir 20–100. **Suspected thrombosis(not proven) was not included as a criterion. ++ Determination of whether the presense of another apparent cause of thrombocytopenia was "possible" or "definite" was at the discretion of the investigator.

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