What is the management of Heparin-Induced Thrombocytopenia (HIT)?

Management of Heparin-Induced Thrombocytopenia (HIT)

The management of Heparin-Induced Thrombocytopenia requires immediate discontinuation of all forms of heparin and initiation of a non-heparin anticoagulant at therapeutic doses. 1

Diagnosis and Assessment

1. Clinical Probability Assessment:

   • Use the 4Ts scoring system to determine pre-test probability:
     • Thrombocytopenia (degree of platelet count fall)
     • Timing of platelet count fall
     • Thrombosis or other sequelae
     • Other causes of thrombocytopenia 2, 1

2. Laboratory Testing:

   • For intermediate/high probability (4T score ≥4):
     • Perform immunological testing for anti-PF4 antibodies
     • If anti-PF4 antibodies are positive, perform functional tests to confirm diagnosis 2
   • For low probability (4T score ≤3):
     • HIT can be excluded without specific bioassays
     • Continue monitoring platelet count and search for other causes of thrombocytopenia 2

Immediate Management

1. Discontinue All Heparin Products:

   • Stop all forms of heparin immediately when HIT is suspected with intermediate/high probability
   • This includes unfractionated heparin (UFH), low molecular weight heparin (LMWH), heparin flushes, and heparin-coated catheters 1
   • Do not wait for laboratory confirmation if clinical suspicion is high 2

2. Initiate Alternative Anticoagulation:

   • Start therapeutic doses of a non-heparin anticoagulant immediately 2, 1
   • Failure to provide alternative anticoagulation increases thrombotic risk 5-fold 1

Alternative Anticoagulant Options

1. First-line Options:

   • Argatroban:

     • Direct thrombin inhibitor indicated for prophylaxis or treatment of thrombosis in HIT 3
     • Initial dose: 2 μg/kg/min as continuous infusion (standard case) 1, 3
     • Reduce initial dose to 0.5 μg/kg/min in critical care/cardiac surgery patients 1
     • Preferred in patients with renal impairment 1
     • Monitor aPTT (target 1.5-2.5 times baseline) 3

   • Bivalirudin:

     • Alternative for severe HIT with massive PE or arterial thrombosis
     • Requires strict biological monitoring 2, 1
     • Can be used in patients with hepatic impairment 1

   • Danaparoid:

     • Not recommended as first-line in severe renal failure 2
     • Must be used at curative IV doses, not prophylactic doses 2
     • Requires monitoring of anti-Xa activity with specific calibration curve 2

   • Fondaparinux:

     • Alternative option, especially in patients with hepatic impairment 1

2. Patient-Specific Considerations:

   • Renal impairment: Prefer argatroban 1
   • Hepatic impairment: Avoid argatroban; use bivalirudin, danaparoid, or fondaparinux 1
   • Severe HIT (massive PE, extensive or arterial thrombosis): Prefer argatroban or bivalirudin with strict monitoring 2, 1

Transition to Oral Anticoagulation

1. Warfarin Transition:

   • Delay warfarin until platelet count recovers to >150 × 10⁹/L 1
   • Overlap with non-heparin anticoagulant for at least 5 days 1
   • Start with low doses of warfarin 1
   • Continue alternative anticoagulant until INR is therapeutic for two consecutive days 4

2. Direct Oral Anticoagulants (DOACs):

   • Stable patients with confirmed HIT may be treated with DOACs like rivaroxaban
   • Dosing: 15 mg twice daily until day 21 or complete platelet recovery, then 20 mg daily 1

Duration of Treatment

• HIT without thrombosis: Minimum 4 weeks of anticoagulation 1
• HIT with thrombosis: Minimum 3 months of anticoagulation 1
• Provoked VTE: Minimum 3 months of anticoagulation 1
• Unprovoked VTE: Consider extended anticoagulation (6-12 months or longer) 1

Monitoring

• Monitor platelet count daily until recovery 1
• Monitor appropriate coagulation parameters based on the anticoagulant used:
  • Argatroban: aPTT (target 1.5-2.5 times baseline) 3
  • Danaparoid: anti-Xa activity with specific calibration 2

Pitfalls and Caveats

1. Do not delay treatment while waiting for laboratory confirmation if clinical suspicion is high 2
2. Avoid platelet transfusions for prophylaxis as they may worsen thrombosis 1, 4
3. Do not start warfarin until platelet count recovers, as it may increase risk of venous limb gangrene 1, 4
4. Do not use prophylactic doses of danaparoid for treatment of acute HIT 2
5. Carefully document the diagnosis in the patient's medical record to prevent future heparin re-exposure 4

By following this algorithmic approach to HIT management, clinicians can reduce the risk of thrombotic complications and improve patient outcomes.