Heparin-Induced Thrombocytopenia (HIT) Overview

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Questions and Answers

What is the most common complication associated with thrombocytopenia in patients suffering from delayed-onset HIT?

  • Deep venous thrombosis (correct)
  • Myocardial infarction
  • Skin necrosis
  • Transient ischemic attack

Which test is specifically designed to measure heparin-dependent platelet activation?

  • 4T scoring test
  • Platelet factor 4 test
  • Anti-PF4 ELISA test
  • Serotonin Release Assay (correct)

Delayed-onset HIT can lead to unexplained thrombocytopenia how long after heparin therapy has ended?

  • 3 weeks (correct)
  • 1 week
  • 4 weeks
  • 2 weeks

The formation of which complex triggers the production of immunoglobulin G antibodies in hit?

<p>PF4-heparin complex (B)</p> Signup and view all the answers

What condition is characterized by an increased likelihood of thrombosis due to platelet activation and aggregation?

<p>Hypercoagulability state (C)</p> Signup and view all the answers

In the pathophysiology of HIT, the binding of antibodies to what triggers premature thrombocyte clearance?

<p>Immune complex (D)</p> Signup and view all the answers

What is a common, yet severe complication of thrombocytopenia resulting from HIT involving limb arteries?

<p>Occlusion of limb arteries (D)</p> Signup and view all the answers

Which of the following is a limitation of the anti-PF4 ELISA test in the diagnosis of HIT?

<p>It is sensitive but not specific (D)</p> Signup and view all the answers

What is the common time frame for the onset of HIT type II symptoms following heparin exposure?

<p>5-14 days (C)</p> Signup and view all the answers

What is the primary action of heparin in the context of thrombosis?

<p>Inhibits the conversion of fibrinogen to fibrin. (B)</p> Signup and view all the answers

What is the complication associated with heparin that leads to decreased platelet counts?

<p>Heparin-induced thrombocytopenia (HIT). (C)</p> Signup and view all the answers

Which of the following treatments is NOT used for managing Heparin-induced Thrombocytopenia (HIT)?

<p>Increase heparin dosage (B)</p> Signup and view all the answers

What should be monitored in patients receiving heparin to assess the risk of HIT?

<p>Platelet counts. (A)</p> Signup and view all the answers

What distinguishes HIT type I from HIT type II?

<p>HIT type I is non-immune mediated; HIT type II is immune-mediated. (C)</p> Signup and view all the answers

How does heparin act as a pro-coagulant in cases of HIT?

<p>Increases platelet aggregation. (B)</p> Signup and view all the answers

In patients with prior exposure to heparin, what is the possibility of rapid-onset HIT?

<p>Can occur within 24 hours if exposed in the last 100 days (C)</p> Signup and view all the answers

At what percentage decrease in platelet count should HIT be suspected?

<p>Over 50% of baseline count. (A)</p> Signup and view all the answers

Which statement about the pathophysiology of HIT is correct?

<p>HIT is caused by the formation of heparin-PF4-IgG complexes. (A)</p> Signup and view all the answers

What is the role of antithrombin III in relation to heparin's mechanism of action?

<p>Inactivates factor Xa. (B)</p> Signup and view all the answers

What is the normal platelet count range in x 10^9 per liter?

<p>150 - 400 (C)</p> Signup and view all the answers

What is a possible consequence of heparin acting as a pro-coagulant in patients with thrombotic events?

<p>Increase in the size of thrombus. (D)</p> Signup and view all the answers

Which diagnostic test is used to confirm the presence of HIT?

<p>Serotonin release assay (B)</p> Signup and view all the answers

How does heparin influence platelet function in HIT type I?

<p>It leads to non-immune-mediated platelet aggregation. (B)</p> Signup and view all the answers

Why is heparin considered an anticoagulant despite its potential to cause HIT?

<p>It primarily inhibits thrombin and factor Xa. (C)</p> Signup and view all the answers

Flashcards

Heparin

An anticoagulant that inhibits thrombin activity and prevents clotting.

Antithrombin III

A protein activated by heparin that inactivates thrombin and factor Xa, preventing clotting.

Fibrinogen

A plasma protein converted into fibrin to form blood clots during coagulation.

Fibrin

The fibrous protein formed from fibrinogen that constitutes the mesh of a blood clot.

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Heparin Induced Thrombocytopenia (HIT)

A complication of heparin leading to a decrease in platelet counts, potentially causing clots instead of preventing them.

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Pro-coagulant

Refers to substances that promote coagulation or the formation of blood clots.

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Platelet Count Monitoring

A vital measurement in patients receiving heparin to detect potential HIT; significant drops indicate risk.

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Side Effects of Heparin

Potential adverse reactions including bleeding and HIT that can occur with heparin use.

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Normal Platelet Count Range

Normal range is 150 - 400 x 10^9 per liter.

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HIT Type I

A mild, transient drop in platelet count early after heparin exposure.

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HIT Type II

An immune-mediated disorder causing significant thrombosis, occurring 5-14 days post-heparin.

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Symptoms of HIT

Trombocytopenia, thrombosis in venous/arterial systems.

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Diagnosis of HIT

Includes clinical scoring, platelet count, and specific serology tests.

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Treatment for HIT

Stop heparin, use alternative anticoagulants, and consider platelet transfusions.

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Rapid-onset HIT

Occurs within 24 hours in patients recently exposed to heparin within 100 days.

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Thrombocytopenia

A condition characterized by low platelet count in the blood, leading to increased bleeding risk.

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Delayed-onset HIT

HIT that occurs 3 weeks after stopping heparin therapy, presenting with thrombosis & thrombocytopenia.

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Heparin-PF4 complex

A complex formed when heparin binds to platelet factor 4, triggering an immune response.

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Immune complex (CIC)

Circulating immune complex formed from antibodies binding to heparin-PF4 complexes.

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Hypercoagulable state

An increased tendency of the blood to clot, often due to HIT.

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4T Score

A clinical scoring system used to diagnose HIT based on thrombocytopenia, timing, thrombosis, and other factors.

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Anti-PF4 test

An ELISA test that detects IgG antibodies against the heparin-PF4 complex for HIT diagnosis.

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Serotonin Release Assay

A functional test measuring platelet activation in response to heparin in HIT diagnosis.

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Study Notes

Heparin-Induced Thrombocytopenia (HIT)

  • HIT is a life-threatening complication of heparin exposure
  • Patients exposed to heparin, regardless of dose, schedule, or route, are at risk
  • Heparin is administered as unfractionated heparin (UFH) or low molecular weight (LMWH) heparin
  • HIT is more common with UFH exposure than LMWH due to greater immunogenicity and cross-reactivity with PF4

Types of HIT

  • HIT Type I (Non-immune):

    • Mild, temporary drop in platelets in the first 2 days of heparin exposure
    • Platelet count returns to normal after heparin is discontinued
    • Direct effect of heparin on platelets, not immune-mediated
    • Not clinically significant

  • HIT Type II (Immune-mediated):

    • Immune-mediated disorder, typically occurring 5-14 days after heparin exposure
    • Significant thrombotic complications (life-threatening)

HIT Type II: Onset

  • Rapid-onset: Can occur in patients with prior heparin exposure within the last 100 days; platelet count can drop within 24 hours of initiating therapy
  • Typical HIT: Onset occurs 5-14 days after heparin therapy begins
  • Delayed-onset: Can develop up to 3 weeks after heparin therapy ends; usually presents with thrombosis and thrombocytopenia

HIT: Clinical Manifestations & Complications

  • Clinical Manifestations:
    • Hypercoagulable state
    • Thrombocytopenia
  • Complications:
    • Deep vein thrombosis (most common)
    • Pulmonary embolism (most common)
    • Myocardial infarction
    • Limb artery occlusion (possible amputation)
    • Transient ischemic attack (TIA) or stroke
    • Skin necrosis
    • End-organ damage (e.g., adrenal, bowel, spleen, gallbladder, or hepatic infarction; renal failure)
    • Death

HIT: Diagnosis

  • 4T score: A clinical scoring system to assess HIT risk
    • Thrombocytopenia (platelet count fall >50% and nadir ≥20 x109/L)
    • Timing of platelet count fall
    • Thrombosis or other sequelae
    • Other causes of thrombocytopenia (none apparent)
  • Diagnostic Assays:
    • Anti-PF4 test: Immunologic assay detecting IgG antibodies against PF4/heparin complex
    • Serotonin Release Assay (SRA): Functional assay measuring heparin-dependent platelet activation (more accurate thrombotic predictor)

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