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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