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Heparin-induced Thrombocytopenia — EECC MCQ

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ModerateCardiac PharmacologyHeparin-induced ThrombocytopeniaEECC

A 62-year-old woman on unfractionated heparin (UFH) infusion for ACS develops an unexplained 50% drop in platelet count (from 220 to 105 × 10⁹/L) on day 6 of therapy. She develops new lower limb DVT. What is the most likely diagnosis and immediate management?

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Correct answer: D — Heparin-induced thrombocytopenia (HIT) type II — stop all heparin immediately and start a non-heparin anticoagulant (argatroban or fondaparinux)

HIT type II is an immune-mediated prothrombotic condition caused by antibodies against the heparin-PF4 complex. Classic features include: (1) platelet count fall >50% from baseline, (2) timing 5-10 days after heparin initiation (or <24h with recent heparin exposure), (3) new thrombosis (paradoxical — despite thrombocytopenia), (4) no other cause. The 4Ts scoring system aids clinical diagnosis. Management requires: (1) immediate cessation of ALL heparin (including flushes), (2) alternative anticoagulation with a non-heparin agent (argatroban IV for critically ill, fondaparinux SC, or bivalirudin), (3) HIT antibody testing (ELISA and serotonin release assay). Warfarin should not be started until platelet recovery (risk of venous limb gangrene). LMWH is NOT an alternative — it cross-reacts with HIT antibodies.

Reference: BSH Guidelines on HIT; NICE NG158