Heparin Induced Thrombocytopenia (HIT)

HEPARIN INDUCED THROMBOCYTOPENIA (HIT)


HEPARIN INDUCED THROMBOCYTOPENIA (HIT)

  • Definition: Heparin-induced thrombocytopenia is an antibody-mediated pro-thrombotic disorder.

Cause:

  • Results due to Ig-G antibody formation to heparin-platelet factor-4 complexes.
  • Antibodies bind platelets & activate them.
  • Results in pro-thrombotic state, even in presence of thrombocytopenia.
  • Usually occurs 5-10 days after exposure to heparins.

Types:

  • 2 types –
  • Type I HIT
  • Type II HIT

Type I HIT:

  • Non-immune mediated reaction.
  • Decrease in platelets is b/w 10-30,000/ml.
    • Platelet drop is due to direct heparin effect on platelet activation.
  • Not of much clinical consequence.
  • Need not discontinue heparin.

Type II HIT:

  • Immune-mediated reaction.
  • Decrease in platelets by 50% or less than 150,000.
  • Heparin needs to be stopped.
  • Alternative anticoagulation needs to be started.

MANAGEMENT:

Treatment initiation criteria: 

  • Increased platelet count, after stopping heparin, in absence of other causes – Diagnostic criteria (even without confirmatory labs).

I) General management:

  • Stop all heparin forms, including LMW Heparins, heparin line flushes or use of heparin-coated catheters.
  • Contraindicated therapies:
  • During this time, certain therapies are contraindicated, including:
    • Platelet transfusions contraindicated.
    • LMWH contraindicated – Due to cross-reactivity.
    • Warfarin (Coumadin) contraindicated initially.

II) Drug therapy:

  • Divided into initial therapy & as continuation therapy.

1. Initial therapy:

  • Direct thrombin inhibitors:
    • Are mainstay therapy.
  • DOC – Lepirudin & Argatroban.
  • Lepirudin –
    • Safe in liver failure.
    • Lepirudin continued till platelet count reaches 1,00,000/µL.
    • Goal aPTT of 1.5-2.5x
    • Side effect – Bleeding (18%).
  • Argatroban
    • Interferes at thrombin active site.
    • Adjusted aPTT of 1.5-3x.
    • Safely administered in anuria (renal failure).
    • Not safe for hepatic failure cases, due to hepatic clearance.
  • Side effect – Bleeding (7%) & anaphylaxis.

2. Continuation therapy:

  • After lepirudin therapy (on direct thrombin inhibitors discontinuation), warfarin therapy started.
  • Reason:
    • Warfarin causes hypercoagulability, hence avoided as initial therapy.
    • Warfarin given for at least 30 days.

3. Other drugs indicated:

  • Xa inhibitors:
    • Drug Fondaparinux & Rivaroxaban
    • Fondaparinux  – Synthetic pentasaccharide.

III) Case-specific management methods:

1. For cases with HIT without thrombosis:

  • Continue anticoagulation, until at least normal platelet count.
  • Increased thrombosis risk for 2-4 weeks.
  • Coumadin for 1-3 month.

2. For cases of HIT with thrombosis:

  • Initiate Coumadin (Only after normal platelet count achieved).
  • Overlap for 5 days with thrombin inhibitor until INR therapeutic. 
  • Continue Coumadin for 3-6 months at INR 2-3.

3. For severe cases with persistent & worsening thrombosis despite HIT treatment.

  • IVIG usage.
  • Plasma exchange.
  • Aspirin, if life-threatening thrombosis.
  • Thrombolysis.
  • Thromboembolectomy.

4. Re-treatment with heparin in known HIT cases:

  • HIT antibodies (IgG or PF4 or heparin) persisting for 100 days/3 months.
  • Heparin is avoided.
  • On mandatory heparin need (As during cardiopulmonary bypass) –
    • Confirm absence of HIT antibodies.
    • Only limited & short-term usage recommended.

5. Preventive strategies:

  • Limit heparin duration (short term recommended).
  • Past HIT history listed as an allergy. 

Exam Important

HEPARIN INDUCED THROMBOCYTOPENIA (HIT)

  • Heparin-induced thrombocytopenia usually occurs 5-10 days after exposure to heparins.
  • Type-1 HIT is a non-immune mediated reaction, resulting in decreased platelet count up to 10-30,000/ml.
  • In type-1 HIT, there is not any need for discontinuation of heparin.
  • Type-2 HIT is an immune-mediated reaction, resulting in decreased platelet count up to 50%, or less than 150,000.
  • In type-2 HIT, heparin is discontinued & alternative anti-coagulant is started.
  • Platelet transfusions, LMWH administration & warfarin usage particularly at initial stages, are all contraindicated during HIT management.
  • Direct thrombin inhibitors are mainstay therapy for HIT management.
  • Drugs included in direct thrombin inhibitors are Lepirudin & Argatroban.
  • Lepirudin & Argatroban are DOC for treating HIT.
  • Lepirudin is safe in liver failure & used for indicated for HIT treatment even during hepatic conditions.
  • During HIT management, lepirudin continued till platelet count reaches 1,00,000/µL.
  • Main goal aimed for lepirudin usage is achieving aPTT levels of 1.5-2.5x.
  • Argatrobanused for HIT treatment nterferes at thrombin active site.
  • During HIT management, only after direct thrombin inhibitors discontinuation (lepirudin therapy)warfarin therapy is started.
  • Main reason “hypercoagulability”.
  • Xa inhibitors like Fondaparinux & Rivaroxaban are used for HIT management.
  • Heparin antibody used during management of HIT is “HIT antibodies”(IgG or PF4 or heparin).

 

Don’t Forget to Solve all the previous Year Question asked on HEPARIN INDUCED THROMBOCYTOPENIA (HIT)

Module Below Start Quiz

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this:
Malcare WordPress Security