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Difficulty: MediumOrdering Laboratory Tests

A 28-year-old woman presents to the emergency department with a 1-day history of sharp, right-sided chest pain that worsens with deep inspiration. She has no cough, hemoptysis, or shortness of breath. Her past medical history is significant for mild asthma, for which she uses an albuterol inhaler as needed. She also takes a combined oral contraceptive pill. She has not had any recent surgeries, and she has not traveled recently. Temperature is 37.1°C (98.8°F), blood pressure is 118/76 mm Hg, pulse is 92/min, and respirations are 16/min. Pulse oximetry is 98% on room air. Physical examination reveals clear lungs bilaterally and a regular heart rhythm without murmurs. There is no calf swelling, tenderness, or erythema. Which of the following is the most appropriate next step in diagnostic evaluation?

  1. A
    Computed tomography pulmonary angiography
  2. B
    Factor V Leiden mutation analysis
  3. C
    Arterial blood gas analysis
  4. D
    Prothrombin time and activated partial thromboplastin time
  5. High-sensitivity D-dimer assayAnswer

Answer

High-sensitivity D-dimer assay
The correct answer is the high-sensitivity D-dimer assay. This patient presents with pleuritic chest pain and has a low pretest probability for pulmonary embolism based on the Wells criteria (score of 0). However, she cannot be entirely ruled out clinically because she fails the Pulmonary Embolism Rule-out Criteria (PERC) due to her use of a combined oral contraceptive pill. According to evidence-based diagnostic algorithms, the most appropriate next step for a low-probability patient who is PERC-positive is a high-sensitivity D-dimer assay. A negative result has a high negative predictive value and safely excludes pulmonary embolism, sparing the patient from radiation and contrast exposure.

Step-by-Step Solution

1
Assess the patient's pretest probability for pulmonary embolism using a validated clinical decision rule (e.g., Wells criteria).
The patient has a Wells score of 0 (no clinical signs of DVT, heart rate < 100, no immobilization, no hemoptysis, no malignancy, alternative diagnosis is possible).
Establishing pretest probability dictates the diagnostic algorithm for suspected pulmonary embolism.
2
Evaluate if the patient meets the Pulmonary Embolism Rule-out Criteria (PERC).
The patient fails the PERC rule solely due to the use of exogenous estrogen (combined oral contraceptive pill).
If a low-probability patient meets all PERC criteria, no testing is needed. Because she fails one criterion, further diagnostic evaluation is required.
3
Select the most appropriate initial test for a low-probability patient who requires further evaluation.
A high-sensitivity D-dimer assay is ordered.
A negative high-sensitivity D-dimer effectively rules out pulmonary embolism in low-probability patients without the need for unnecessary radiation or contrast exposure.

Key Concept

In patients with a low pretest probability for pulmonary embolism who do not meet all rule-out criteria, a high-sensitivity D-dimer assay is the most appropriate initial diagnostic laboratory test.
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Ordering Laboratory Tests

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