How to treat Heparin-Induced Thrombocytopenia (HIT)?

Treatment of Heparin-Induced Thrombocytopenia (HIT)

For patients with suspected or confirmed HIT, immediately discontinue all forms of heparin and initiate a non-heparin anticoagulant at therapeutic intensity. 1

Diagnosis and Initial Management

1. Suspect HIT when:

   • Platelet count falls by ≥50% or below normal range
   • Thrombosis develops while on heparin
   • Timing is typically 5-14 days after heparin initiation (or sooner with recent heparin exposure)

2. Immediate actions:

   • Stop ALL heparin products (including flushes and heparin-coated catheters)
   • Obtain baseline aPTT before starting alternative anticoagulation 2
   • Order immunoassay for anti-PF4/heparin antibodies 1

Non-Heparin Anticoagulant Selection

For patients with normal renal function:

• Argatroban: Initial dose 2 mcg/kg/min as continuous IV infusion 2
  • Target aPTT 1.5-3× baseline (not exceeding 100 seconds)
  • Check aPTT 2 hours after initiation and after any dose change
  • Maximum dose: 10 mcg/kg/min 3

For patients with renal insufficiency:

• Argatroban: Preferred due to hepatic metabolism 1
  • Initial dose 0.5-2 mcg/kg/min IV 1
  • Monitor aPTT as above

For patients with hepatic impairment:

• Adjust argatroban dosing for moderate to severe hepatic impairment 2
• Consider alternative agents if severe hepatic dysfunction

Monitoring Therapy

• Check aPTT 2 hours after initiation and after any dose changes 2
• Target aPTT: 1.5-3× baseline value (not exceeding 100 seconds) 2
• Steady-state levels typically reached within 1-3 hours of initiation 2
• Assess for thrombosis, as up to 50% of untreated HIT patients develop thrombotic events 4

Transition to Oral Anticoagulation

1. Wait for platelet recovery before starting vitamin K antagonists (VKAs):

   • Platelet count should recover to >150 × 10^9/L 3, 1
   • If VKA was already started when HIT diagnosed, administer vitamin K 3

2. When initiating warfarin:

   • Start with low doses (maximum 5 mg) 3
   • Overlap parenteral non-heparin anticoagulant with VKA for at least 5 days 3
   • Continue overlap until INR is therapeutic for two consecutive days 5
   • Recheck INR after discontinuing the non-heparin anticoagulant 3

Duration of Treatment

• For HIT with thrombosis (HITT): Continue VKA therapy for at least 3-6 months
• For isolated HIT (without thrombosis): Continue anticoagulation for at least 4 weeks 3

Special Considerations

• Avoid platelet transfusions unless life-threatening bleeding is present 3, 1
• Document HIT diagnosis in medical records and provide patient with medical alert card 1
• Delay elective procedures until HIT antibodies are negative (typically >3 months) 1
• For patients requiring cardiac surgery with history of HIT:
  • If antibodies negative (>100 days), intraoperative UFH may be used
  • Use alternative anticoagulants pre- and post-operatively 5

Treatment Efficacy

Studies show that patients with HIT treated with direct thrombin inhibitors have approximately five-fold lower risk of thrombosis compared to those who just have heparin discontinued 1. Argatroban reduces the risk of new thrombosis by 55-70% compared to heparin discontinuation alone 3, 1.

Common Pitfalls to Avoid

1. Do not continue any form of heparin once HIT is suspected
2. Do not start VKA before platelet count recovers (can precipitate venous limb gangrene)
3. Do not interpret elevated INR as therapeutic when patient is on both DTI and warfarin
4. Do not give platelet transfusions for prophylaxis in HIT
5. Do not restart heparin in patients with history of HIT

Following these evidence-based guidelines will help minimize morbidity and mortality in patients with this potentially life-threatening condition.