The Question
A 62-year-old man presents 7 days after elective total knee arthroplasty with acute left calf pain and swelling. His postoperative course included low-molecular-weight heparin prophylaxis. He is afebrile, HR 88 bpm, BP 132/78 mmHg, RR 16. Exam shows a tender swollen left calf with erythema. Laboratory data: platelet count was 250,000/µL preoperatively and is now 95,000/µL, hemoglobin 13.2 g/dL, creatinine 0.9 mg/dL; PT and aPTT are within reference range. Duplex ultrasound shows an occlusive left popliteal vein deep venous thrombosis. Peripheral smear demonstrates reduced platelets without schistocytes. He is not bleeding. Which of the following is the most appropriate next step in management?
See the answer and explanation below:
Post-Call Recovery Reads
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A
Explanation
High-Yield Pearl: In suspected heparin-induced thrombocytopenia (HIT) with new thrombosis, immediately stop all heparin and begin a non-heparin parenteral anticoagulant such as argatroban while sending PF4 immunoassay and a functional confirmatory test.
Detailed Reasoning: The timing (5–10 days after heparin exposure), a >50% fall in platelet count from baseline, and a new occlusive DVT create a high pretest probability for HIT, and guidelines (ASH/ACCP) recommend prompt cessation of all heparin and initiation of alternative anticoagulation rather than waiting for the assay. Argatroban (a direct thrombin inhibitor) is an appropriate immediate choice in a patient with normal hepatic and renal function; fondaparinux or bivalirudin are alternative agents. Starting warfarin acutely without a non-heparin parenteral anticoagulant is contraindicated because initial warfarin therapy can worsen a hypercoagulable state and precipitate venous limb gangrene; warfarin is started only after platelet recovery and with overlap. Platelet transfusion is generally avoided in HIT unless there is life-threatening bleeding because it can accelerate thrombosis. Obtaining PF4 ELISA is appropriate, but deferring treatment until results return risks further thrombotic events; the immunoassay is sensitive but not specific and should be confirmed with a functional assay such as the serotonin release assay. While DOACs have emerging data for HIT management, current guideline-based practice for acute HIT with thrombosis favors starting a parenteral non-heparin anticoagulant initially.
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