Hematology Oncology · Year 2 · from Hematology Oncology

Case 3: Heparin-Induced Thrombocytopenia

Patient Presentation

Demographics: 67-year-old male

Chief Complaint: Leg pain and declining platelet count during hospitalization

History of Present Illness: The patient is hospitalized following coronary artery bypass grafting (CABG) 8 days ago. He has been receiving unfractionated heparin for DVT prophylaxis since admission. Today, nursing noted he has new left calf swelling and pain. Review of labs shows his platelet count has fallen from a post-operative baseline of 180,000/uL to 62,000/uL today (65% decline over 4 days). He has no bleeding symptoms.

Physical Examination:

• Vital signs: BP 138/82, HR 88, RR 16, Temp 37.4C
• General: Post-operative male, appropriate recovery
• Cardiovascular: Healing sternotomy, regular rhythm
• Left leg: Swelling, warmth, calf tenderness
• Skin: No petechiae or ecchymoses; IV site erythema at previous heparin infusion site

Workup and Results

Laboratory Trends:

4Ts Score:

• Thrombocytopenia: 2 points (50-70% fall)
• Timing: 2 points (day 5-10 of heparin)
• Thrombosis: 2 points (new DVT confirmed)
• Other causes: 2 points (no other obvious cause)
• Total: 8 points (HIGH probability)

HIT Testing:

• Anti-PF4/heparin ELISA: Positive (OD 2.1)
• Serotonin release assay: Positive (95% release)

Imaging:

• Compression ultrasound: Left popliteal vein DVT confirmed

Clinical Image

Graph showing characteristic platelet count decline in heparin-induced thrombocytopenia, typically occurring 5-10 days after heparin initiation with greater than 50% fall from baseline.

Diagnosis

Heparin-Induced Thrombocytopenia (HIT) Type II with DVT

Diagnostic criteria:

• Timing: Platelet decline days 5-10 after heparin exposure
• Magnitude: >50% fall from post-operative peak
• Thrombosis: New DVT despite prophylaxis
• High 4Ts score (8 points)
• Laboratory confirmation with positive ELISA and SRA

Treatment Plan

1. Immediate actions:

• STOP ALL HEPARIN (including flushes, heparin-coated catheters)
• Document HIT allergy in medical record

1. Alternative anticoagulation:

• Start argatroban (direct thrombin inhibitor) IV infusion
• Target aPTT 1.5-3x baseline
• Continue until platelets recover >150,000/uL

1. Transition to long-term anticoagulation:

• Once platelets >150,000/uL, may transition to warfarin
• Overlap argatroban with warfarin for 5+ days
• INR target 2.0-3.0
• Duration: Minimum 3 months for HIT with thrombosis

1. Do NOT:

• Transfuse platelets (may worsen thrombosis)
• Use LMWH (cross-reacts with HIT antibodies)
• Start warfarin before platelet recovery (risk of limb gangrene)

1. Future precautions:

• Lifetime avoidance of heparin
• HIT antibodies wane after ~100 days but re-exposure can cause rapid-onset HIT

Teaching Points

1. HIT is an immune-mediated prothrombotic disorder, NOT a bleeding disorder despite low platelets
2. Antibodies form against PF4-heparin complexes and activate platelets, causing consumption AND thrombosis
3. The 4Ts score helps estimate pre-test probability and guide testing
4. HIT typically occurs 5-10 days after heparin exposure; rapid-onset HIT occurs with recent prior exposure
5. Thrombosis occurs in 30-50% of untreated HIT cases, both venous and arterial
6. Platelet transfusion is contraindicated as it may fuel further thrombosis
7. Warfarin should not be started until platelets recover due to protein C depletion and limb gangrene risk
8. Alternative anticoagulants include argatroban, bivalirudin, and fondaparinux

All cases for this lecture as Markdown