4Ts score for heparin-induced thrombocytopenia
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When to use
Thrombocytopenia
Platelet count fall > 50% from baseline and platelet nadir ≥ 20×10**9/L
Platelet count fall 30-50% from baseline or platelet nadir 10-19×10**9/L
Platelet count fall < 30% from baseline or platelet nadir < 10×10**9/L
Timing of platelet count fall
Clear onset between days 5-10 or platelet fall ≤ 1 day with prior heparin exposure within 30 days
Consistent with onset days 5-10, but not clear or onset after day 10 of heparin exposure or fall ≤ 1 day with prior heparin exposure 30-100 days ago
< 4 days without recent exposure.
Thrombosis or other sequelae
New thrombosis, skin necrosis, or acute systemic reaction after unfractionated heparin exposure
Progressive/recurrent thrombosis or unconfirmed but clinically suspected thrombosis
No thrombosis or thrombosis preceding heparin exposure
Other causes for thrombocytopenia
None apparent
Possible other causes
Probable other causes
Calculation
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