What precautions should be taken in patients at risk of heparin-induced thrombocytopenia (HIT)?

Precautions for Patients at Risk of Heparin-Induced Thrombocytopenia (HIT)

For patients at risk of HIT, platelet count monitoring should be performed every 2-3 days from day 4 to day 14 of heparin therapy when the risk of HIT is >1%, and nonheparin anticoagulants should be used if HIT is suspected or confirmed. 1

Risk Assessment and Monitoring

• Assess the risk of HIT before initiating heparin therapy - patients with >1% risk require platelet count monitoring every 2-3 days from day 4 to day 14 of therapy 1
• Patients with <1% risk of HIT do not require routine platelet count monitoring 1
• Monitor for clinical signs of HIT including unexplained thrombocytopenia, venous or arterial thrombosis, skin lesions, or acute systemic reactions after IV heparin bolus 1

Immediate Actions When HIT is Suspected

• Immediately discontinue all forms of heparin (including heparin flushes and heparin-coated catheters) when HIT is suspected 1
• Initiate alternative nonheparin anticoagulation even before laboratory confirmation due to the high thrombotic risk 1
• Obtain baseline aPTT before starting alternative anticoagulation 2
• Perform laboratory testing for HIT antibodies to confirm diagnosis 1

Alternative Anticoagulation Options

For Patients with Normal Renal Function:

• Use argatroban, lepirudin, or danaparoid as first-line therapy 1
• Dosing considerations:
  • Argatroban: Initial dose 2 mcg/kg/min as continuous infusion 2
  • Monitor aPTT and adjust dose as clinically indicated 2

For Patients with Renal Impairment:

• Use argatroban as the preferred agent due to hepatic clearance 1, 2
• Adjust starting dose and titrate carefully in patients with moderate or severe hepatic impairment 2

For Patients Requiring Urgent Cardiac Surgery:

• Use bivalirudin if surgery cannot be delayed 1
• If possible, delay cardiac surgery until HIT has resolved and HIT antibodies are negative 1

For Patients Requiring Percutaneous Coronary Intervention:

• Use bivalirudin (Grade 2B) or argatroban (Grade 2C) 1
• For argatroban in PCI: Start at 25 mcg/kg/min with a bolus of 350 mcg/kg administered over 3-5 minutes 2
• Check ACT 5-10 minutes after bolus; proceed if ACT >300 seconds 2

Management of Vitamin K Antagonist (VKA) Therapy

• Do not start VKA until platelets have substantially recovered (usually to at least 150 × 10^9/L) 1
• When starting VKA, use low initial doses (maximum 5 mg warfarin or 6 mg phenprocoumon) 1
• If VKA has already been started when HIT is diagnosed, administer vitamin K 1
• Overlap VKA with a nonheparin anticoagulant for a minimum of 5 days and until the INR is within target range 1
• Recheck INR after the anticoagulant effect of the nonheparin anticoagulant has resolved 1

Special Considerations

• For severe thrombocytopenia, give platelet transfusions only if bleeding occurs or during invasive procedures with high bleeding risk 1
• Monitor for hemorrhage when using alternative anticoagulants, especially in patients receiving antiplatelet agents, thrombolytics, or other anticoagulants 2
• For patients with a history of HIT requiring anticoagulation, prefer oral anticoagulants (VKA or DOACs) or fondaparinux 1
• Provide patients with a medical card documenting their HIT history and laboratory test results 1
• Perform a sensitive biological test (ELISA) to confirm absence of PF4-specific antibodies before any further exposure to heparin 1

Prevention Strategies

• Limit heparin exposure to the shortest possible duration (<4-5 days) 1
• Consider using oral anticoagulants or LMWH instead of unfractionated heparin when possible 1
• Prescribe heparin only for validated indications 1