Intern Report 3/1 – HIT

Teaching Points

  • Pathogenesis of HIT
    • Antibody formation to the PF4/heparin complex, causing platelet aggregation.
  • Two types of HIT
    • Type I – immediate decrease of platelet count after use of heparin. Not due to action of antibody
    • Type II – due to action of antibody directed against the PF4/heparin complex
  • Clinical Manifestations
    • Thrombocytopenia
      • >50% decrease in platelet count (even if there is no evidence of thrombocytopenia)
      • Or to a nadir of 40k
    • Thrombosis
      • According to studies, 20-50% of patients diagnosed with HIT are found to have HITT (heparin-induced thrombocytopenia AND thrombosis)
      • May be venous or arterial thrombosis
    • Timing
      • Classically begins 5-10 days after use of heparin
      • But can also present immediately if patient was exposed to heparin within the last 100 days.
    • Rule out other causes
  • Work-up
    • 4T’s score (thrombosis, thrombocytopenia, timing, rule out oTher causes)
    • Score >3/8 indicates moderate to high pre-test probability for HIT
    • Score less than 3 has a high NPV for not having HIT.
    • Score >3/8 – Send off HIT antibody
      • HIT antibody has  high sensitivity. Negative HIT antibody means the patient does not have heparin induced thrombocytopenia.
      • If positive, send off serotonin release assay (confirmatory test – high specificity)
    • Start anticoagulation with argatroban given high risk of thrombosis
      • Argatroban will also increase INR.
      • Treat until platelet count >150k or reaches it’s plateau
      • Then transition them to Coumadin
        • Treat with anticoagulation for 1 month if no thrombosis
        • Treat with anticoagulation for 3 months if there is thrombosis

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