Evaluation of Pulmonary Embolism in Low-Risk Patients

Assessment of Pretest Probability

The American College of Physicians recommends determining the pretest probability of pulmonary embolism using validated clinical prediction rules or clinician gestalt, as seen in this 28-year-old female patient with only one PERC criterion and no other concerning features 1, 2
The patient's symptoms improved with Flonase, suggesting allergic rhinitis as the likely cause of her shortness of breath, which is consistent with a low pretest probability for pulmonary embolism 3
Based on these factors, patients with low pretest probability, such as this patient, would be classified as having a low risk for pulmonary embolism 1, 3

The Pulmonary Embolism Rule-Out Criteria (PERC) include age >49, pulse >99, O2 saturation <95%, hemoptysis, exogenous estrogen, prior VTE, recent surgery/trauma, and unilateral leg swelling, which can help identify low-risk patients in whom the risk of testing outweighs the risk of pulmonary embolism 4, 5
A meta-analysis of 12 studies found that the overall proportion of missed pulmonary embolisms using PERC was only 0.3% (44 of 14,844 cases), indicating the effectiveness of PERC in ruling out pulmonary embolism in low-risk patients 5

For patients with low pretest probability who do not meet all PERC criteria, the next step would typically be D-dimer testing, but this test has low specificity and can lead to unnecessary imaging if positive 6
The American College of Physicians guidelines emphasize avoiding unnecessary testing in low-risk patients, such as this 28-year-old female patient with a clear alternative diagnosis and only one PERC criterion 2

Unnecessary D-dimer testing can lead to false-positive results and subsequent CT imaging, which exposes the patient to radiation and contrast risks 3, 6
The risk of missing pulmonary embolism in low-risk patients, such as this patient, is extremely low given their age, single risk factor, and symptom improvement with appropriate treatment for allergic rhinitis 3, 5