Heparin-Induced Thrombocytopenia (HIT)

Falling platelet count + recent heparin exposure (UFH > LMWH, 4–14 days post-exposure typically). Paradoxically thrombotic — DVT/PE/arterial. 4Ts score: • Thrombocytopenia: >50% fall + nadir ≥20 (2); 30–50% fall OR nadir 10–19 (1); <30% fall OR nadir <10 (0). • Timing onset: 5–10 days OR <1 day with heparin in last 30 days (2); >10 days OR fall <5 days but unclear prior exposure (1). • Thrombosis OR sequelae: new thrombosis / skin necrosis (2); progressive / recurrent / silent / cutaneous reaction (1). • OTher cause: none apparent (2); possible (1); definite (0). Score: ≤3 low probability (1%), 4–5 intermediate (10%), ≥6 high (>50%).