A 68-year-old woman is evaluated in the hospital on postoperative day 7 following an elect… — USMLE Step 2 CK

A $68$ -year-old woman is evaluated in the hospital on postoperative day $7$ following an elective right total hip arthroplasty. Since the surgery, she has been receiving subcutaneous enoxaparin for deep venous thrombosis prophylaxis. She now reports new-onset right leg pain and swelling that began this morning. Temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $132/82\text{ mm Hg}$ , pulse is $92/\text{min}$ , and respirations are $16/\text{min}$ . Physical examination shows a swollen, erythematous right lower extremity with tenderness to palpation over the calf and thigh.

Laboratory studies:
Hemoglobin: $11.2\text{ g/dL}$
Leukocyte count: $7,800/\text{mm}^3$
Platelet count: $52,000/\text{mm}^3$ (Preoperative platelet count was $260,000/\text{mm}^3$ )

A lower extremity venous duplex ultrasound reveals a noncompressible segment in the right femoral vein consistent with an acute deep venous thrombosis. Which of the following is the most appropriate next step in management?

A
Discontinue enoxaparin and initiate warfarin
B
Continue enoxaparin and increase to a therapeutic dose
Discontinue enoxaparin and initiate argatrobanAnswer
D
Discontinue enoxaparin and place an inferior vena cava filter
E
Discontinue enoxaparin and transfuse platelets

Answer

Discontinue enoxaparin and initiate argatroban

This patient's presentation of a new deep venous thrombosis (DVT) accompanied by a sudden, significant drop in platelets (

>50\%

) occurring

7

days after starting enoxaparin is highly suspicious for Heparin-Induced Thrombocytopenia (HIT) Type 2. HIT is a prothrombotic, autoimmune disorder caused by antibodies against the heparin-platelet factor 4 (PF4) complex. The most appropriate next step in management for a patient with a high pretest probability of HIT is the immediate discontinuation of all heparin products (including low-molecular-weight heparins like enoxaparin) and the initiation of a non-heparin anticoagulant, such as the direct thrombin inhibitor argatroban or bivalirudin.

Step-by-Step Solution

Evaluate the timing and severity of thrombocytopenia in conjunction with the new thrombosis.

The patient meets criteria for a high probability of Heparin-Induced Thrombocytopenia (HIT) based on the 4T score: a

>50\%

platelet drop, symptom onset between days

5

10

of therapy, and a new acute thrombosis.

A high pretest probability mandates immediate changes to clinical management before awaiting confirmatory laboratory testing.

Discontinue the offending pharmacological agent.

Subcutaneous enoxaparin (a low-molecular-weight heparin) must be stopped immediately.

Continuing any heparin product will propagate the immune-mediated platelet activation and worsen the condition.

Initiate alternative systemic anticoagulation.

A non-heparin anticoagulant, such as the direct thrombin inhibitor argatroban, is initiated.

Patients with HIT are highly prothrombotic and require immediate alternative anticoagulation to prevent or treat life-threatening clots.

Key Concept

Patients with suspected Heparin-Induced Thrombocytopenia (HIT) must have all heparin products immediately discontinued and be started on a non-heparin anticoagulant, such as argatroban.

Alternative Method

The 4T score (Thrombocytopenia, Timing, Thrombosis, and oTher causes) can be quickly calculated to establish pretest probability. A score of 6-8 indicates high probability, warranting immediate action before laboratory confirmation via serotonin release assay or PF4 ELISA.

Estimated Time:1m 15s

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