Heparin-induced thrombocytopenia

Background

• Despite low plt count pt is actually hypercoagulable; bleeding is unusual
• Pathophysiology
  • Pathologic activation / consumption of platelets due to Ab against heparin-plt complex
  • Activated platelets then cause blood clot formation
    • Platelet count falls b/c plts are bound in clots
  • Can be caused by unfrationated or LMWH (10x common in the former)
    • Occurs in 0.5-5% of pts tx'd w/ heparin
• Thrombosis occurs in 35-75% of pts; 20-30% die w/in 1 month

Clinical Features

• Typical
  • Symptoms begin 5-10d after initiation of heparin
    • >50% decrease in plt count (median nadir is ~60K; rarely <20K)
    • DVT or PE
    • Cerebral vein or adrenal vein thrombosis
    • Limb arterial occlusion
    • CVA
    • MI
    • Skin necrosis
• Rapid onset
  • Symptoms begin within hours of initiation of heparin
    • Due to preexisting circulating antibody from sensitization several weeks earlier
    • Sudden drop in plt count
    • Thrombosis
    • Flushing
    • Tachycardia
    • Hypotension
    • Dyspnea
• Delayed onset
  • Symptoms begin several days after heparin stopped
  • Severe thromboses

Diagnosis

• Serotonin release assay (SRA) = gold standard
  • Positivity determined by optical density (OD) reported w/ assay (same concept as a titer)
    • OD <1 = <5% chance of HIT
    • OD 1.4 = 50% chance of HIT
    • OD >2 = 90% chance of HIT

Treatment

1. Discontinue all heparin products
2. Do not give platelts (may precipitate thrombosis)
3. Start anticoagulation
   1. Consider direct thrombin inhibitor [lepirudin (unless renal failure), argatroban (unless hepatobiliary disease), bivalirudin] or direct Xa inhibitor (fondaparinux, danaparoid)
   2. Avoid warfarin until platelets >100K-150K

Dispostion

• Admit

See Also

• Unfractionated Heparin
• Low Molecular Weight Heparin
• Coagulopathy (Main)

Source

Tintinalli