Diagnostic Approach for Suspected Pulmonary Embolism
Use the pulmonary embolism rule-out criteria (PERC) to exclude pulmonary embolism, and if PERC-positive, proceed with D-dimer testing followed by CT pulmonary angiography if the D-dimer is positive.
Clinical Risk Stratification First
This patient requires initial clinical probability assessment before any testing. She presents with chest pain, shortness of breath, and tachycardia (HR 108 bpm) but lacks high-risk features such as hemoptysis, prior VTE, recent surgery/trauma, or unilateral leg swelling 1. Her smoking history is relevant but she appears hemodynamically stable 1.
Apply PERC Criteria
The PERC rule should be applied first in this patient who appears to have low-to-intermediate clinical probability 2. The 8 PERC criteria are:
- Age <50 years (she is 49 - meets this)
- Heart rate <100/min (she has HR 108 - does NOT meet this)
- Oxygen saturation >94% (not provided, but no hypoxemia mentioned)
- No hemoptysis (confirmed)
- No estrogen use (no medications mentioned)
- No prior VTE (confirmed)
- No unilateral leg swelling (confirmed)
- No recent surgery or trauma (confirmed)
Since she fails at least one PERC criterion (tachycardia >100 bpm), she is PERC-positive and requires further testing 2, 3.
D-dimer Testing Strategy
For PERC-positive patients with low-to-intermediate pretest probability, D-dimer is the appropriate next step 4, 2. The American College of Physicians specifically recommends obtaining high-sensitivity D-dimer measurement as the initial diagnostic test in patients with intermediate pretest probability, and imaging studies should not be used as the initial test 4.
- If D-dimer is negative (<500 ng/mL, or age-adjusted cutoff of 490 ng/mL for her age of 49), PE is safely excluded without imaging 4, 3, 5
- If D-dimer is positive, proceed to CT pulmonary angiography 4, 2
Why Not Direct CTPA?
Going directly to CT pulmonary angiography without D-dimer testing exposes patients to unnecessary radiation and contrast nephropathy risk 4. In hemodynamically stable patients with low or intermediate clinical likelihood of PE, normal D-dimer results obviate the need for PE imaging 1. The diagnostic strategy of D-dimer followed by CT is cost-effective and has the lowest cost per life saved for all patients suspected with PE 6.
Why Not V/Q Scan First?
V/Q scanning is reserved as an alternative when CT pulmonary angiography is contraindicated (severe contrast allergy, renal failure, pregnancy concerns) 1, 4. CTPA is now the primary imaging modality for evaluating patients suspected of having acute PE 1. V/Q scans are frequently non-diagnostic (intermediate probability results) and require further investigation 1, 7.
Critical Pitfall
The most common error is proceeding directly to CTPA in all patients with suspected PE 4. This approach misses the opportunity to safely exclude PE with D-dimer testing alone in approximately 30-50% of patients, thereby avoiding unnecessary radiation exposure, contrast administration, incidental findings, and healthcare costs 5, 6.