A 62-year-old woman is evaluated in the hospital on hospital day 6 for new-onset shortness… — USMLE Step 2 CK

A $62$ -year-old woman is evaluated in the hospital on hospital day $6$ for new-onset shortness of breath and right-sided pleuritic chest pain. She was initially admitted for a deep venous thrombosis of the left lower extremity and was started on a continuous infusion of unfractionated heparin. Her past medical history is notable for hypertension and type 2 diabetes mellitus. Temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure is $134/82\text{ mmHg}$ , pulse is $112\text{/min}$ , and respirations are $22\text{/min}$ . Pulse oximetry shows $92\%$ on room air. Physical examination reveals clear lungs bilaterally and swelling of the left leg that is unchanged from admission.

Laboratory studies obtained today show:

Laboratory Test	Result
Hemoglobin	$12.1\text{ g/dL}$
Leukocyte count	$7,800/\mu\text{L}$
Platelet count	$105,000/\mu\text{L}$
Prothrombin time	$12\text{ s}$
Partial thromboplastin time	$58\text{ s}$

On admission, her platelet count was $240,000/\mu\text{L}$ . Which of the following is the most appropriate next step in management?

Discontinue unfractionated heparin and initiate argatrobanAnswer
B
Discontinue unfractionated heparin and initiate enoxaparin
C
Continue unfractionated heparin and order a serotonin release assay
D
Discontinue unfractionated heparin and monitor for spontaneous recovery
E
Transfuse one unit of apheresis platelets and order computed tomography pulmonary angiography

Answer

Discontinue unfractionated heparin and initiate argatroban

The correct action is to stop unfractionated heparin and begin argatroban. This patient presents with a classic picture of Type 2 Heparin-Induced Thrombocytopenia (HIT) complicated by a likely new pulmonary embolism. The 4T score is high due to a >50% drop in platelets occurring between days 5-10 of heparin therapy, accompanied by new thrombosis. Type 2 HIT is an immune-mediated disorder where IgG antibodies form against the heparin-platelet factor 4 (PF4) complex. This activates platelets, leading to a highly prothrombotic state rather than a bleeding diathesis. Management dictates the immediate cessation of all heparin exposure and empiric initiation of a non-heparin anticoagulant, most commonly a direct thrombin inhibitor (argatroban, bivalirudin) or fondaparinux, while awaiting confirmatory testing (like the serotonin release assay).

Step-by-Step Solution

Calculate the magnitude and timing of the platelet drop.

The platelet count dropped from 240,000/μL to 105,000/μL (a >50% decrease) precisely between days 5 and 10 of heparin therapy.

This specific timing and degree of thrombocytopenia are the clinical hallmarks of Type 2 Heparin-Induced Thrombocytopenia (HIT).

Assess for new clinical complications.

The patient has tachycardia, hypoxia, and pleuritic chest pain, which is highly suspicious for a new pulmonary embolism.

HIT is a prothrombotic state, and new thrombosis (HITT) solidifies the clinical diagnosis and increases urgency.

Determine the optimal immediate therapeutic intervention.

All heparin products must be ceased immediately, and a non-heparin anticoagulant (such as a direct thrombin inhibitor like argatroban) must be started.

Empiric treatment must begin prior to laboratory confirmation to prevent life-threatening thrombotic events.

Key Concept

Type 2 Heparin-Induced Thrombocytopenia requires immediate cessation of all heparin products and initiation of a non-heparin anticoagulant (e.g., argatroban, bivalirudin, or fondaparinux).

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