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Difficulty: MediumHematology and Oncology

A 62-year-old woman is evaluated on postoperative day 6 following a right total knee arthroplasty. Since the surgery, she has been receiving subcutaneous unfractionated heparin for deep vein thrombosis prophylaxis. Today, she reports new-onset left calf pain and swelling.

Vital signs are within normal limits. Physical examination reveals left calf tenderness, erythema, and 2+ pitting edema up to the knee.

Laboratory studies on admission:
Hemoglobin: 13.2 g/dL
Leukocyte count: 8,500/mm³
Platelet count: 260,000/mm³

Laboratory studies today:
Hemoglobin: 12.8 g/dL
Leukocyte count: 9,200/mm³
Platelet count: 110,000/mm³

A duplex ultrasonography of the left lower extremity demonstrates a noncompressible popliteal vein. Which of the following is the most appropriate next step in management?

  1. Discontinue unfractionated heparin and initiate argatrobanAnswer
  2. B
    Discontinue unfractionated heparin and initiate warfarin
  3. C
    Switch unfractionated heparin to enoxaparin
  4. D
    Transfuse irradiated pooled platelets
  5. E
    Continue unfractionated heparin and obtain a CT pulmonary angiogram

Answer

Discontinue unfractionated heparin and initiate argatroban
This patient's presentation of a >50% drop in platelets occurring 5-10 days after heparin initiation, combined with a new deep vein thrombosis, is highly suggestive of type 2 heparin-induced thrombocytopenia (HIT). HIT is an immune-mediated disorder caused by antibodies against heparin-platelet factor 4 (PF4) complexes, which activate platelets and create a profound prothrombotic state. The most critical next step is to immediately discontinue all heparin products and initiate non-heparin anticoagulation, such as a direct thrombin inhibitor (e.g., argatroban, bivalirudin) or an indirect factor Xa inhibitor (e.g., fondaparinux).

Step-by-Step Solution

1
Calculate the 4T score for Heparin-Induced Thrombocytopenia.
The patient has a platelet count drop of >50% (2 points), timing between days 5 and 10 (2 points), new thrombosis (2 points), and no other clear cause (2 points), yielding a high probability score.
To determine the pretest probability of HIT before changing therapy.
2
Determine the immediate management for high-probability HIT.
Stop the offending agent (heparin) and start a direct thrombin inhibitor (argatroban).
Continuing heparin worsens the thrombosis, and untreated HIT carries a high risk of catastrophic thrombotic events.

Key Concept

Diagnosis and management of Heparin-Induced Thrombocytopenia (HIT)
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Topics

Hematology and Oncology

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