Episode 017: Heme/Onc Emergencies, Pt. 6: Heparin-Induced Thrombocytopenia (HIT)

What this episode covers

Emergencies happen in hematology and oncology. This is a fact. But how do we manage these emergencies? Look no further. In this episode, we talk all about our third hematologic emergency: heparin-induced thrombocytopenia (HIT)! Be sure to check out episode 009 on thrombocytopenia for a general approach and differential! HIT: - Any time a patient with heparin exposure and now with a new thrombotic event, you need to think about HIT! What is HIT? - Type 1: a transient drop in platelets after heparin is started - Type 2: **The scary one! Antibody-mediated process **Heparin molecules bind to platelet-factor 4 (PF4) **This complex activates platelets, which then further releases more PF4 from the platelets What is the difference between HIT and HITT? - HITT is when there is also thrombosis (HIT + Clot) Why is this more common in the cardiac ICU? - It is believed that IgM interacts with ultra-long complexes, which heparin is - Lots of heparin is required for cardiac surgery - Therefore lots of exposure to heparin increases likelihood, increasing likelihood for IgM to IgG class-switching; HIT is IgG-mediated process ** Remember - since this is antibody-mediated, therefore it takes a few days for the antibodies to form in patient with a new diagnosis of HIT! How to stratify? 4-T score (MDCalc Link: https://www.mdcalc.com/4ts-score-heparin-induced-thrombocytopenia) Workup: - Sent HIT ELISA test in patient with high suspicion - ELISA just suggests if the HIT antibody is present - If ELISA positive, then do confirmatory assay, i.e., is this antibody actually doing anything, is the "serotonin-release assay” - Send 4 extremity dopplers to look for thrombosis - STOP heparin/heparin-derived products and SWITCH anticoagulant, such as argatroban, fondaparinux, bivalirudin (do not wait for a positive test if your suspicion is high enough!) If HIT positive: - Add heparin to their allergy list - Continue anticoagulation until platelets are recovered (>150K) - Continue anticoagulation for 3-6 months for patients with HITT Words of wisdom: If patient comes from outside hospital and starts having decreasing platelets, consider HIT in your differential! References: https://ashpublications.org/blood/article/119/10/2209/29530/How-I-treat-heparin-induced-thrombocytopenia- great review article from ASH on HIT Please visit our website (TheFellowOnCall.com) for more information Twitter: @TheFellowOnCall Instagram: @TheFellowOnCall Listen in on: Apple Podcast, Spotify, and Google Podcast