heparin induced thrombocytopenia and thrombosis HIT

type 1 HITT

  • within 2 days of initiating heparino
  • transient, non pathologic
  • Plt > 100k
  • Do not stop heparin, plt will return to normal

type 2 HITT

  • antibody against PF4 => activates Plt => plt cascades => thrombosis and thrombocytopenia
  • risks
    • women
    • most often unfractionated heparin
    • CV surgery, ortho surgery, increased trauma severity
    • more or longer heparin => more likely to get HITT
  • patients with endothelial damage
  • clotting is worse than bleeding
  • arterial and venous clot
    • Thrombocytopenia - platelets typically decline >30%-50%
    • Timing - onset 5-10 days after heparin initiation or <1 day with prior, recent heparin exposure
    • Thrombosis - new thrombosis, progressive thrombosis, or skin necrosis
    • Alternative causes - no other sources for thrombocytopenia are present or likely
  • interpret based on 4T score
    • e.g. low 4T with positive test: 1% chance positive HITT
  • Diagnosis is confirmed with serotonin release assays (preferred), heparin-induced platelet aggregation assays, or solid-phase immunoassays with ELISA for heparin-PF4 complexes.
  • Stop argatroban: when Plt > 150k, then switch to DOAC or warfarin for minimum of 6 months. Initial treatment with warfarin is contraindicated as rapidly dropping protein C levels cause a prothrombotic state.  Warfarin is usually started after the patient is treated with a non-heparin anticoagulant and recovers a platelet count to > 150,000/µL.

Delayed onset HIT

Delayed-onset HIT - immune mediated due to high-titer antibodies against heparin-PF4 complexes in the absence of circulating heparin.  Cases typically arise 5-19 days after heparin cessation; therefore, most patients present in the outpatient setting.  Thrombocytopenia with or without life-threatening arterial or venous thrombosis are the norm.

[!NOTE] extensive DVT with thrombocytopenia after major surgery in clinic