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5 Pearls on Heparin-Induced Thrombocytopenia

STEP 1: Listen to the podcast

STEP 2 (Members Only): Take the CME/MOC Quiz

Show Notes

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. 
    • Surgical patients are at higher risk than medical patients
    • Low-molecular weight heparin (e.g. enoxaparin) is less likely to cause HIT than unfractionated heparin 

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 sensitivity for a diagnosis of HIT is cited as 98-100%, while the specificity is in the 30-40% range.
    • The poor specificity comes from people who form antibodies against PF4 that don’t activate platelets and therefore don’t cause thrombocytopenia or thrombosis. 
  • 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.

Disclosures

Contributors

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

Reviewers

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

CME Credit

This activity has been planned and implemented in accordance with the accreditation requirements and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint providership of the American College of Physicians and Core IM.  The American College of Physicians is accredited by the ACCME to provide continuing medical education for physicians.

The American College of Physicians designates each enduring material (podcast) for 1 AMA PRA Category 1 Credit™.  Physicians should claim only the credit commensurate with the extent of their participation in the activity.

ABIM Maintenance of Certification (MOC) Points

Successful completion of this CME activity, which includes participation in the evaluation component, enables the participant to earn up to 1 medical knowledge MOC Point in the American Board of Internal Medicine’s (ABIM) Maintenance of Certification (MOC) program.  Participants will earn MOC points equivalent to the amount of CME credits claimed for the activity. It is the CME activity provider’s responsibility to submit participant completion information to ACCME for the purpose of granting ABIM MOC credit.

How to Claim CME Credit and MOC Points

After listening to the podcast, complete a brief multiple-choice question quiz.  To claim CME credit and MOC points you must achieve a minimum passing score of 66%.  You may take the quiz multiple times to achieve a passing score.

About Core IM

Welcome to Core IM, a virtual medical community! Core IM strives to empower its colleagues of all levels and backgrounds with clinically applicable information as well as inspire curiosity and critical thinking. Core IM promotes its mission through podcasts and other multimodal dialogues. ACP has teamed up with Core IM to offer continuing medical education, available exclusively to ACP members by completing the CME/MOC quiz.


Details

CME/MOC:

Up to 1 AMA PRA Category 1 Credits ™ and MOC Points
Expires November 13, 2022   active

Cost:

Free to Members

Format:

Podcasts and Audio Content

Product:

Core IM

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