How critical is it to order a D-dimer (D-dimer test) to rule out pulmonary embolism (PE) in a 28-year-old female with Nexplanon (etonogestrel implant) and intermittent shortness of breath with activity, who has shown improvement with Flonase (fluticasone propionate) for suspected allergic rhinitis?

D-dimer Testing in a 28-year-old Female with Nexplanon and Intermittent Shortness of Breath

D-dimer testing is not critical in this case as the patient meets all PERC criteria except for Nexplanon use, has improvement with Flonase suggesting allergic rhinitis as the cause, and has a low pretest probability for pulmonary embolism.

Assessment of Pretest Probability

• The first step in evaluating suspected PE is to determine the pretest probability using validated clinical prediction rules or clinician gestalt 1
• This 28-year-old female has only one PERC criterion (exogenous estrogen via Nexplanon) and no other concerning features 1
• Her symptoms improved with Flonase, suggesting allergic rhinitis as the likely cause of her shortness of breath 1
• Based on these factors, she would be classified as having a low pretest probability for PE 1

Application of PERC Criteria

• The Pulmonary Embolism Rule-Out Criteria (PERC) were developed to identify low-risk patients in whom the risk of testing outweighs the risk of PE 1
• PERC criteria include: age >49, pulse >99, O2 saturation <95%, hemoptysis, exogenous estrogen, prior VTE, recent surgery/trauma, and unilateral leg swelling 1
• This patient meets 7 of 8 PERC criteria (only failing on exogenous estrogen due to Nexplanon) 1
• A meta-analysis of 12 studies found that the overall proportion of missed PEs using PERC was only 0.3% (44 of 14,844 cases) 1

D-dimer Testing Considerations

• For patients with low pretest probability who do not meet all PERC criteria, the next step would typically be D-dimer testing 1
• However, D-dimer testing has low specificity and can lead to unnecessary imaging if positive 1
• The improvement of symptoms with Flonase suggests an alternative diagnosis (allergic rhinitis) that adequately explains her symptoms 1
• In patients with a clear alternative diagnosis and only one PERC criterion, the value of D-dimer testing is limited 1

Risk-Benefit Analysis

• Unnecessary D-dimer testing can lead to false-positive results and subsequent CT imaging 1
• CT imaging exposes the patient to radiation and contrast risks 1
• The risk of missing PE in this patient is extremely low given her age, single risk factor, and symptom improvement with appropriate treatment for allergic rhinitis 1
• The American College of Physicians guidelines emphasize avoiding unnecessary testing in low-risk patients 1

Special Considerations for Nexplanon

• While Nexplanon (etonogestrel implant) is a form of exogenous estrogen and a risk factor for PE, it is the patient's only risk factor 2
• Pulmonary embolization of the Nexplanon device itself is extremely rare and typically presents with chest pain or dyspnea that doesn't improve with allergy treatment 2
• The patient's improvement with Flonase strongly suggests allergic rhinitis as the cause of symptoms rather than PE 1

Conclusion

• In this specific case, D-dimer testing is not critical and can be safely deferred 1
• Clinical follow-up is appropriate to ensure continued improvement with Flonase 1
• If symptoms worsen or fail to improve with appropriate treatment for allergic rhinitis, reassessment of PE risk and potential D-dimer testing could be considered 1