4Ts Score for Heparin-Induced Thrombocytopenia
Differentiates patients with HIT from those with other causes of thrombocytopenia.
When to Use
Platelet count fall >50% AND platelet nadir ≥20+2
Platelet count fall 30–50% OR platelet nadir 10–19+1
Platelet count fall <30% OR platelet nadir <100
Clear onset between days 5–10 OR platelet fall ≤1 day (prior heparin exposure within 30 days)+2
Consistent with days 5–10 fall, but not clear; onset after day 10 OR fall ≤1 day (prior heparin exposure 30–100 days ago)+1
Platelet count fall <4 days without recent exposure0
New thrombosis OR skin necrosis; acute systemic reaction post-IV heparin bolus+2
Progressive OR recurrent thrombosis; non-necrotizing skin lesions; suspected thrombosis (not proven)+1
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