Episode 017: Heme/Onc Emergencies, Pt. 6: Heparin-Induced Thrombocytopenia (HIT)
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)
In case you were curious what Dan was wearing in this episode … and where Vivek records our show from!
Heparin-induced thrombocytopenia (HIT):
Be sure to check out episode 009 on thrombocytopenia for a general approach and differential!
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 (link here)
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
