Heparin Induced Thrombocytopenia (HIT) - Diagnosis and Management - GrepMed Handbook
Presentation:
• Plts ↓50% (nadir ~40-80k) after 5-10d, venous (DVT/PE) or arterial thrombosis, skin necrosis (at injection sites)
↑ Risk Factors:
• SICU > MICU, ♀, ↑Age, ESRD
Pathophysiology:
• IgG binds heparin-PF4 complex → plt activation and PF4 release → hypercoagulable state and plt consumption → thrombocytopenia
Diagnosis:
• Clinical Suspicion → Calculate 4T score (0-8).
• If 4T score ≥ 4, obtain Anti-PF4 Ab titer (ELISA) - ↑Sens/↓Spec → Significant false ⊕’s, so use Bayesian approach for post-test probability (IBCC).
• Serotonin Release Assay (SRA): Confirmatory test ↑Se/Sp but very slow - do not wait to treat if high suspicion.
Management:
• D/c all heparin (including flushes), reverse any warfarin exposure (prevent skin necrosis)
• Start non-heparin A/C if clinical thrombosis or high likelihood of HIT: Argatroban, Fondaparinux, Bivalirudin, DOAC
• A/C Duration:
⊕Thrombosis: 6 months
⊖Thrombosis: Min until Plts recover, consider a/c 2-3m (↑ thrombosis w/in 30d)
• H/o HIT: Can consider re-challenge >100d after Dx if PF4-Ab⊖ or SRA⊖.
Check out https://emcrit.org/ibcc/thrombocyto for a definitive guide to diagnosis and management of HIT
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