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Table 2 HIT 4Ts score

From: A case of heparin-induced thrombocytopenia (HIT) triggered by methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia

4Ts category 2 points 1 points 0 points
Thrombocytopenia Platelet count decrease >50 % and platelet nadir >20 × 109 L−1 Platelet count decrease 30–50 % or platelet nadir 10–19 × 109 L−1 Platelet count decrease <30 % or platelet nadir <10 × 109 L−1
Timing of the platelet count decrease Clear onset days 5–10 or platelet decrease <1 day (prior heparin exposure within 30 days) Consistent with the day 5–10 decrease, but not clear; onset after day 10, or decrease <1 day (prior heparin exposure 30–100 days ago) Platelet count decrease <4 days without recent heparin exposure
Thrombosis or other sequelae New thrombosis (confirmed); skin necrosis; acute systemic reaction to the post-intravenous unfractionated heparin bolus Progressive or recurrent thrombosis; non-necrotizing (erythematous) skin lesions; suspected thrombosis (not proven) None
Other causes of thrombocytopenia None apparent Possible Definite
  1. Total score ≤3 low probability of HIT, 4–5 intermediate probability of HIT, ≥6 high probability of HIT