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/thrombocytopenia/#heparin_induced_thrombocytopenia for a definitive guide to diagnosis and management of HIT



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