5 Pearls on Heparin-Induced Thrombocytopenia
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Pearl 1: Pathophys and Epidemiology
- HIT is as an antibody-mediated activation of platelets with heparin exposure that results in thrombocytopenia, and in some cases, venous or arterial thrombosis
- We care about HIT because it is associated with a 6% daily risk of thrombosis, amputation and death if left untreated.
- HIT causes thrombosis by activating platelets to release pro-thrombotic substances via a complex of heparin, platelet factor 4 (PF4), and antibody (usually IgG).
- It generally takes 5-10 days for people to develop antibodies against heparin to cause HIT. However, if people have been exposed to heparin in recent past, they may already have antibodies against PF4 and can have rapid-onset HIT after heparin exposure.
- The overall incidence of HIT ranges from anywhere between 0.1% to 5%, depending on the patient population and the type of heparin being used.
Pearl 2: The 4T Score
- The 4T score includes the degree of thrombocytopenia, the timing of platelet decrease, the presence of thrombosis, and considering the likelihood of other etiologies of thrombocytopenia.
- Consider using a systematic approach to thinking about thrombocytopenia.
- Decreased production: liver disease (decreased thrombopoietin), bone marrow hypoplasia (from meds, toxins, infections, pregnancy), ineffective erythropoiesis (megaloblastic anemia, MDS), and bone marrow infiltration (cancer, infection, myelofibrosis)
- Increased destruction: hypersplenism, ITP, the thrombotic microangiopathies (TMAs), and HIT
- Many medications can cause thrombocytopenia without causing thrombosis. Be sure to review medications 1-2 weeks prior to thrombocytopenia, not 1-2 days prior. A database of drugs that have been reported to do this can be found here.
Pearl 3: Testing for HIT
- The anti-PF4 antibody test is an ELISA-based assay that detects circulating antibody that binds to PF4
- The serotonin release assay (SRA) is a much more specific test for HIT and is the gold standard for diagnosis currently
- The SRA measures serotonin release from platelets in a heparin-dependent manner
- The main limitation is that it usually takes several days to 1 week to result
Pearl 4: Treatment of HIT
- Stopping heparin is not enough. If you’re testing for HIT, generally you should be treating HIT with anticoagulation.
- The type of anticoagulant is going to depend on a few different factors: how quickly you need to be able to reverse or turn off the anticoagulant (high bleeding risk, upcoming procedures, critical illness), and their liver and kidney function.
- Quick on/off, reversible: argatroban, bivalirudin
- Slow on/off: DOACs (rivaroxaban, apixaban), fondaparinux
- Liver dysfunction: avoid argatroban
- Starting warfarin is contraindicated until platelet count has recovered to ~>150k as it can increase the risk of thrombosis (HIT patients are very dependent on protein C to prevent thrombosis).
- Treatment duration depends on if the patient has HIT complicated by thrombosis, or isolated HIT.
- With HIT with thrombosis, treating as if they have a “provoked” clot for 3 months is appropriate.
- For HIT without thrombosis, there isn’t a real consensus, but treating at least until their platelet count recovers is what most hematologists recommend, and sometimes up to 4-6 weeks.
Pearl 5: Throwback to Coronary Calcium Score
- Coronary calcium scoring should only be used to risk-stratify asymptomatic patients if the results may influence the initiation of primary prevention medications.
- Power of a calcium score of ZERO: statins are not associated with a reduction in major adverse events in this group and can consider discontinuing a statin.
Joel Money, MD - Host, Editor
Marty Fried, MD - Host, Editor
*Adam Cuker, MD - Guest
Lori-Ann Linkins, MD - Guest
Shreya Trivedi, MD - Host, Editor, CME Questions
Jacques Azzi, MD
**Allyson Pishko, MD
Those named above unless otherwise indicated have no relationships to disclose.
* Adam Cuker, MD, disclosed research grants/contracts from Alexion, Bayer, NovoNordisk, Pfizer, Sanofi, Spark, and Takeda and consultantship from Synergy CRO.
** Allysion Pishko, MD, disclosed research grants/contracts from NovoNordisk and Sanofi Genzyme
Release Date: November 13, 2019
Expiration: November 13, 2022
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