Heparin-induced thrombocytopenia in solid organ transplant recipients: The current scientific knowledge

Table 1 The 4Ts scoring system[62]

Parameter	2 points	1 point	0 points
Thrombocytopenia	Platelet count drop > 50% and platelet nadir ≥ 20 g/L	Platelet count drop 30%-50% or platelet nadir 10-19 g/L	Platelet count drop < 30% or platelet nadir < 10 g/L
Timing of platelet count drop	Onset on days 5-10 or platelet count drop ≤ 1 d and previous heparin exposure < 30 d ago	Onset on days 5-10 but platelet count drop not clear (e.g., missing counts); onset after day 10 of heparin therapy or drop ≤ 1 d and previous heparin exposure 30-100 d ago	Platelet count drop ≤ 4 d after beginning of heparin therapy and no previous heparin exposure
Thrombosis and sequelae	New proven thrombosis; skin necrosis; acute systemic reaction after heparin application	Progressive or recurrent thrombosis; suspected thrombosis; non-necrotizing skin lesions	None
Other causes of thrombocytopenia	Apparently none	Possible	Definite

Probability of HIT II: 1-3 points: Low; 4-5 points: Intermediate; 6-8 points: High. HIT: Heparin-induced thrombocytopenia.