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Difficulty: MediumHematology and Oncology

A 6262-year-old man is evaluated on postoperative day 66 following a right total knee arthroplasty. He complains of new-onset swelling and pain in his right calf. The patient has been receiving subcutaneous unfractionated heparin for deep venous thrombosis prophylaxis since his surgery. He has no other medical history and takes no other medications. Vital signs are normal. Physical examination shows a swollen, erythematous, and tender right calf.

Laboratory results:

TestResult
Hemoglobin13.2 g/dL13.2 \text{ g/dL}
Platelet count (Day 0)260,000/μL260,000/\mu\text{L}
Platelet count (Day 6)110,000/μL110,000/\mu\text{L}

A duplex ultrasound of the right lower extremity reveals a new noncompressible segment in the right popliteal vein. Which of the following is the most appropriate next step in the management of this patient?

  1. A
    Discontinue unfractionated heparin and initiate enoxaparin
  2. B
    Continue unfractionated heparin and order a serotonin release assay
  3. Discontinue unfractionated heparin and initiate argatrobanAnswer
  4. D
    Discontinue unfractionated heparin and initiate warfarin
  5. E
    Transfuse a single unit of apheresis platelets

Answer

Discontinue unfractionated heparin and initiate argatroban
This patient's presentation is highly characteristic of Heparin-Induced Thrombocytopenia (HIT) type 2. HIT is an immune-mediated, prothrombotic disorder caused by the development of IgG antibodies against heparin-platelet factor 4 (PF4) complexes. It is classically suspected when a patient experiences a platelet count drop of greater than 50%50\% from baseline, typically occurring 55 to 1010 days after the initiation of unfractionated or low-molecular-weight heparin. This patient's count dropped from 260,000/μL260,000/\mu\text{L} to 110,000/μL110,000/\mu\text{L} on day 66. Furthermore, the condition paradoxically causes severe thrombosis rather than bleeding, evidenced here by the new popliteal deep venous thrombosis. When HIT is clinically suspected (e.g., high 4T score), immediate empiric treatment is required before waiting for confirmatory laboratory testing. All heparin products must be immediately discontinued. Because the patient has a new thrombosis and remains at high risk for further clots, therapeutic anticoagulation must be rapidly established using a non-heparin agent. Direct thrombin inhibitors (such as argatroban or bivalirudin) or the indirect factor Xa inhibitor fondaparinux are the preferred therapies.

Step-by-Step Solution

1
Calculate the magnitude of the platelet drop and note the timing.
The platelet count dropped by more than 50%50\% (from 260,000260,000 to 110,000110,000) over 66 days of heparin therapy.
A >50%>50\% drop in platelets occurring 55 to 1010 days after heparin initiation strongly suggests Heparin-Induced Thrombocytopenia (HIT).
2
Assess for clinical complications associated with the thrombocytopenia.
The patient has a new deep venous thrombosis (DVT) in the popliteal vein.
HIT is a highly prothrombotic state. The combination of typical timing, severe platelet drop, and new thrombosis yields a high '4T' score, making HIT the presumptive diagnosis.
3
Determine the necessary immediate medical intervention.
All heparin products must be stopped immediately, and therapeutic anticoagulation with a non-heparin agent (e.g., argatroban) must be started.
Stopping heparin halts the immune reaction, and a direct thrombin inhibitor provides the necessary anticoagulation to treat the new DVT without cross-reacting with HIT antibodies.

Key Concept

Patients who develop a >50%>50\% drop in platelets and new thrombosis 5−105-10 days after starting heparin have Heparin-Induced Thrombocytopenia (HIT). Management requires immediate cessation of all heparin products and initiation of a non-heparin anticoagulant like argatroban.
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Topics

Hematology and Oncology

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