Diagnostic Approach for Moderate Pretest Probability PE
For a 34-year-old woman with pleuritic chest pain and moderate pretest probability for pulmonary embolism, obtain a high-sensitivity D-dimer test first—if negative (using age-adjusted cutoff of age × 10 ng/mL, though at age 34 this equals 340 ng/mL, which is below the standard 500 ng/mL threshold), no imaging is needed; if positive, proceed directly to CT pulmonary angiography. 1
Initial Risk Stratification
The American College of Physicians explicitly recommends that clinicians obtain a high-sensitivity D-dimer measurement as the initial diagnostic test in patients who have an intermediate (moderate) pretest probability of PE. 1 Imaging studies should not be used as the initial test in patients with intermediate pretest probability. 1
D-dimer Testing Strategy
Age-Adjusted Thresholds
- For patients over 50 years, use an age-adjusted D-dimer cutoff calculated as age × 10 ng/mL rather than the generic 500 ng/mL cutoff. 1
- For this 34-year-old patient, the standard 500 ng/mL threshold applies since age-adjustment only benefits those over 50. 1, 2
- A D-dimer below the cutoff safely excludes PE without any imaging. 1
If D-dimer is Elevated
- Any D-dimer level above the threshold in a moderate pretest probability patient requires imaging. 2
- Proceed directly to CT pulmonary angiography (CTPA). 1
Imaging When Indicated
First-Line Imaging
- CTPA is the primary imaging modality for patients with moderate pretest probability and positive D-dimer. 1, 3
- CTPA has high sensitivity (>95%) for segmental or larger emboli and provides the ability to identify alternative diagnoses. 1
Alternative Imaging Options
If CTPA is contraindicated (contrast allergy, renal dysfunction, pregnancy):
- Ventilation-perfusion (V/Q) scan is the first-line alternative. 1, 4
- Lower extremity venous ultrasound can be considered as a complementary test—a positive DVT finding provides evidence of venous thromboembolic disease and may preclude need for pulmonary imaging. 1, 5
Critical Pitfalls to Avoid
Do Not Skip D-dimer in Moderate Probability
- Unlike high pretest probability patients (where imaging should be obtained directly without D-dimer), moderate probability patients benefit from D-dimer risk stratification. 1
- D-dimer testing in moderate probability patients prevents unnecessary imaging in those with negative results. 1, 6
Do Not Order Imaging First
- Starting with CTPA in moderate probability patients exposes those with negative D-dimers to unnecessary radiation, contrast nephropathy risk, and incidental findings requiring follow-up. 1
- The radiation exposure is particularly concerning in young women due to radiosensitive breast tissue. 1
Recognize Pleuritic Chest Pain Significance
- The presence of pleuritic chest pain in this patient is highly suggestive of PE and commonly associated with pleural effusion when PE is present. 7
- Nearly all pleural effusions due to PE are exudates and frequently hemorrhagic. 7
Clinical Context
This algorithmic approach balances diagnostic accuracy with patient safety by avoiding overuse of CT imaging, which has increased dramatically without corresponding improvements in mortality. 1 The strategy is cost-effective and reduces exposure to radiation and contrast-related complications while maintaining diagnostic sensitivity through appropriate D-dimer utilization. 1