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 plateletsWhat 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 HITTWords 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 HITPlease visit our website (TheFellowOnCall.com) for more information Twitter: @TheFellowOnCallInstagram: @TheFellowOnCallListen in on: Apple Podcast, Spotify, and Google Podcast