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
- Thrombocytopenia
- 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