Vancouver IM LMR

Dr. Eric Zhao (PGY5 in Hematology) gave a riveting talk on anti-PF4-antibody disorders, including classic HIT (heparin-induced thrombocytopenia), autoimmune HIT, VITT (vaccine-induced immune thrombotic thrombocytopenia), and VITT-like disorders. We really appreciated Dr. Zhao’s deep understanding of the immune pathophysiology behind these disorders!

See the didactic slide deck here.

Key takeaways:

• HIT (heparin-induced thrombocytopenia)
  • UFH >> LMWH >> fondaparinux
  • Platelet count decreases > 50% and/ or new thrombotic complications between day 5-14 of being on UFH or LMWH. Once the heparin is stopped, platelets should start to recover because the immune stimulus is removed.
  • If the patient has received heparin within the last 100 days, they may still have circulating antibodies against it, so rapid-onset HIT (platelet drop in 1 day) is possible.
  • Diagnosis:
    • Screen with the 4T score
    • If intermediate-high risk, order a serotonin-release assay (SRA) which is the confirmatory test (it is an ELISA test)
  • Management:
    • STOP heparin
    • SWITCH to alternate non-heparin anticoagulant (argatroban is the only FDA-approved agent; off-label use for bivalirudin and fondaparinux)
    • DO NOT give warfarin; if patient is on warfarin should reverse with vitamin K (repletion of protein C&S can cause skin necrosis)
    • DO NOT give prophylactic platelet transfusions which can add fuel to the fire
    • Send for ultrasound for lower-limb DVT which can be clinically silent
• Autoimmune HIT
  • Triggered by heparin but then can develop heparin-independent antibodies (causing thrombotic complications) and can last for life!
• VITT and VITT-like disorders
  • Triggered by adenovirus vector vaccines and adenovirus infections creating heparin-independent antibodies