In a 20‑year‑old previously healthy female with two days of fever, cough, congestion, sore throat, left‑lower‑chest pain, normal vital signs, normal chest X‑ray and a Wells score of 1.5 (low pre‑test probability), what is the next step to safely rule out pulmonary embolism?

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Last updated: March 18, 2026 • View editorial policy

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Next Step: Obtain High-Sensitivity D-Dimer Testing

In this 20-year-old with a Wells score of 1.5 (low pretest probability) and suspected PE, you should obtain a high-sensitivity D-dimer measurement as the next diagnostic step. 1

Algorithmic Approach

Step 1: Assess if PERC Criteria Apply

With a low pretest probability (Wells score 1.5), first determine if the patient meets all 8 Pulmonary Embolism Rule-Out Criteria (PERC): 1

  • Age <50 years ✓ (patient is 20)
  • Heart rate <100 bpm ✓ (HR is 90)
  • Oxygen saturation ≥95% (need to verify)
  • No hemoptysis (appears absent from history)
  • No estrogen use (need to verify)
  • No prior DVT/PE (previously healthy)
  • No unilateral leg swelling (not mentioned)
  • No surgery/trauma requiring hospitalization within 4 weeks (not mentioned)

Critical Point: If this patient meets ALL 8 PERC criteria, no further testing (including D-dimer or imaging) should be performed, as the risk of PE is lower than the risks of testing. 1 The pooled sensitivity of PERC is 97% with only 0.3% of PEs missed when properly applied. 1

Step 2: If PERC Criteria Are Not All Met

Proceed with high-sensitivity D-dimer testing as the initial diagnostic test. 1 This is the American College of Physicians' Best Practice Advice 3, which explicitly states clinicians should obtain D-dimer in patients with low pretest probability who do not meet all PERC criteria. 1

Step 3: Interpret D-Dimer Results

  • If D-dimer is <500 ng/mL: PE is ruled out; no imaging is needed. 1 The negative predictive value is sufficient to exclude PE safely. 1

  • If D-dimer is ≥500 ng/mL: Proceed to CT pulmonary angiography (CTPA). 1

Note on Age-Adjusted Cutoffs: Since this patient is only 20 years old, the age-adjusted D-dimer threshold (age × 10 ng/mL = 200 ng/mL) would be lower than the standard 500 ng/mL cutoff. 1 However, age-adjusted cutoffs are recommended for patients older than 50 years to increase specificity while maintaining sensitivity above 97%. 1 For this young patient, use the standard 500 ng/mL cutoff.

Why Not Imaging First?

Do not proceed directly to CTPA or other imaging in this low-probability patient. 1 The American College of Physicians explicitly states that imaging studies should not be used as the initial test in patients with low or intermediate pretest probability. 1

The rationale includes: 1

  • Radiation exposure carries cancer risk, particularly concerning in young women with radiosensitive breast tissue
  • Contrast nephropathy risk from CT contrast dye
  • Increased healthcare costs without proven mortality benefit
  • High rate of incidental findings requiring unnecessary follow-up
  • Evidence suggests increased CT use has not improved PE-related mortality despite detecting more (often less severe) PEs

Common Pitfalls to Avoid

  1. Misapplying PERC: PERC should only be used in patients where you have genuine clinical concern for PE but low pretest probability—not as a universal screening tool. 1 When properly applied, PERC can safely avoid 22% of unnecessary D-dimer tests. 1

  2. Ordering imaging despite normal D-dimer: Studies show many clinicians inappropriately proceed to CT despite normal D-dimer levels in low-risk patients, contrary to guidelines. 1 A normal D-dimer in this setting has sufficient negative predictive value to exclude PE. 1

  3. Skipping clinical probability assessment: Always use validated prediction rules (Wells, Geneva) or structured clinical judgment before ordering any tests. 1, 2 This prevents both over-testing and under-diagnosis.

Clinical Context

This patient's presentation (fever, cough, congestion, sore throat) suggests an upper respiratory infection as the more likely diagnosis, with pleuritic chest pain potentially from viral pleuritis or musculoskeletal causes. 3 The normal chest X-ray and stable vital signs (temperature now 37.2°C, normal heart rate and blood pressure) support a lower-risk presentation. 3, 2

References

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