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Difficulty: HardHematology and Oncology

A 6868-year-old man is evaluated on postoperative day 66 following an elective right total hip arthroplasty. He reports new-onset right calf pain and swelling that began this morning. His temperature is 38.1∘C38.1^\circ\text{C} (100.6∘F100.6^\circ\text{F}), blood pressure is 130/80130/80 mmHg, pulse is 9898/min, and respirations are 1616/min. Physical examination reveals a swollen, tender right calf with mild erythema. Since admission, the patient has been receiving subcutaneous enoxaparin for deep vein thrombosis prophylaxis. Laboratory studies show:

IndicatorValue
Hemoglobin12.412.4 g/dL
Platelet count105,000/μL105,000/\mu\text{L} (Baseline on admission: 260,000/μL260,000/\mu\text{L})
Leukocyte count9,500/μL9,500/\mu\text{L}
Serum creatinine1.11.1 mg/dL

A venous Doppler ultrasound of the right lower extremity confirms an acute deep venous thrombosis in the popliteal vein. Which of the following is the most appropriate next step in management?

  1. Discontinue enoxaparin and initiate argatrobanAnswer
  2. B
    Discontinue enoxaparin and initiate unfractionated heparin
  3. C
    Continue enoxaparin and initiate warfarin
  4. D
    Continue enoxaparin and administer broad-spectrum antibiotics
  5. E
    Discontinue enoxaparin and administer a platelet transfusion

Answer

Discontinue enoxaparin and initiate argatroban
The correct approach involves immediately stopping all heparin products and starting a non-heparin anticoagulant, such as the direct thrombin inhibitor argatroban. This patient has classic features of Heparin-Induced Thrombocytopenia (HIT) Type 2: a >50%>50\% drop in platelet count occurring 55 to 1010 days after the initiation of a heparin product (enoxaparin), accompanied by a new thrombotic event (DVT). HIT is an immune-mediated disorder caused by IgG antibodies against the heparin-platelet factor 4 (PF4) complex, which activates platelets and triggers widespread thrombosis. Because enoxaparin is the inciting agent, it must be discontinued. However, the patient remains at a very high risk for further life-threatening thromboses, so a non-heparin alternative must be started promptly.

Step-by-Step Solution

1
Analyze the clinical presentation and timing.
Postoperative day 6 patient with a new deep vein thrombosis (DVT) and low-grade fever.
To establish the acute clinical problem requiring management.
2
Evaluate the laboratory findings in context.
Platelet count dropped from 260,000/μL260,000/\mu\text{L} to 105,000/μL105,000/\mu\text{L} (a >50%>50\% decrease) while on enoxaparin.
To identify potential complications of pharmacological prophylaxis.
3
Synthesize findings to formulate a diagnosis.
The timing (5-10 days post-exposure), >50%>50\% platelet drop, and new thrombosis are highly suggestive of Heparin-Induced Thrombocytopenia (HIT) Type 2.
To determine the underlying pathophysiology of the new DVT.
4
Determine the appropriate management for the diagnosis.
All heparin products (including LMWH) must be stopped immediately, and a non-heparin anticoagulant like a direct thrombin inhibitor (e.g., argatroban) must be started.
To prevent further immune-mediated platelet activation and thrombosis.

Key Concept

Diagnosis and management of Heparin-Induced Thrombocytopenia (HIT) Type 2
Estimated Time:1m 30s
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Topics

Hematology and Oncology

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