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