What is the best diagnostic approach for a suspected pulmonary embolism in an adult patient?

Diagnostic Approach for Suspected Pulmonary Embolism

Begin with validated clinical prediction rules (Wells score or revised Geneva score) to stratify pretest probability, then proceed with D-dimer testing (using age-adjusted thresholds for patients >50 years) for low/intermediate probability patients, or proceed directly to CT pulmonary angiography for high probability patients. 1

Risk Stratification Using Clinical Prediction Rules

All patients with suspected PE must be stratified using validated clinical decision tools before ordering any tests. 1, 2

• Wells Score assigns points for: clinical signs of DVT (3 points), PE as likely diagnosis as or more likely than alternative (3 points), heart rate >100 (1.5 points), immobilization/surgery in past 4 weeks (1.5 points), previous PE/DVT (1.5 points), hemoptysis (1 point), and malignancy (1 point) 3
• Low probability: Wells score ≤4 or simplified Geneva score 0-1 (PE prevalence ~3-13%) 2, 3
• Intermediate probability: Wells score 2-6 or simplified Geneva score 2-4 (PE prevalence ~16-26%) 2
• High probability: Wells score >6 or simplified Geneva score ≥5 (PE prevalence ~36-50%) 2, 3

Diagnostic Algorithm by Risk Category

Low Pretest Probability Patients

Apply the Pulmonary Embolism Rule-Out Criteria (PERC) before ordering any laboratory tests. 1, 4

• PERC criteria (all 8 must be met): age <50 years, heart rate <100 bpm, oxygen saturation ≥95% on room air, no unilateral leg swelling, no hemoptysis, no recent trauma/surgery within 4 weeks, no prior VTE history, and no hormone use 2, 4
• If all 8 PERC criteria are met: PE is ruled out, no further testing needed 1, 2
• If any PERC criterion is not met: Proceed to high-sensitivity D-dimer testing 1, 2

Critical pitfall: PERC should only be applied to patients already determined to have low pretest probability—never use it as a general screening tool 2

Intermediate Pretest Probability Patients

Proceed directly to high-sensitivity D-dimer testing without applying PERC. 1, 2

High Pretest Probability Patients

Proceed directly to CT pulmonary angiography (CTPA) without D-dimer testing. 1, 2, 3

• A negative D-dimer cannot safely exclude PE when pretest probability is high 2, 3
• Ordering D-dimer in high probability patients wastes time and resources 2

D-Dimer Testing and Interpretation

Use only high-sensitivity D-dimer assays (ELISA or turbidimetric methods) with sensitivity ≥95%. 2

Age-Adjusted D-Dimer Thresholds

For patients >50 years old, use age-adjusted D-dimer cutoff (age × 10 ng/mL) instead of the standard 500 ng/mL threshold. 1, 2

• Patients ≤50 years: Use standard cutoff <500 ng/mL 2, 3
• Patients >50 years: Use age-adjusted cutoff (age × 10 ng/mL) 1, 2
• Age-adjusted thresholds maintain sensitivity >97% while significantly improving specificity, which drops to only 10% in patients >80 years using standard cutoffs 2
• This approach increases the proportion of older patients in whom PE can be excluded from 6.4% to 30% without additional false-negative findings 2

D-Dimer Results

• If D-dimer is below the appropriate threshold: PE is ruled out, no imaging needed (negative predictive value 99.5%) 2, 4, 3
• If D-dimer is elevated: Proceed immediately to CTPA 2, 3

Critical pitfall: Never use positive D-dimer alone to diagnose PE—confirmation with imaging is mandatory 3

Imaging Studies

CT Pulmonary Angiography (CTPA)

CTPA is the imaging test of first choice with sensitivity 83% and specificity 96%. 3, 5, 6

• Indications for CTPA: High pretest probability patients (without D-dimer) or low/intermediate probability patients with elevated D-dimer 1, 3
• Positive CTPA: Segmental or more proximal filling defect confirms PE diagnosis without further testing 3
• Negative CTPA: In low/intermediate probability patients, effectively rules out PE without additional testing 3, 5
• Negative CTPA in high probability patients: Consider additional testing such as compression ultrasonography of lower extremities 3

Ventilation-Perfusion (V/Q) Scanning

Reserve V/Q scanning for patients with contraindications to CTPA (renal insufficiency, contrast allergy) or when CTPA is unavailable. 1, 3

• V/Q SPECT has the lowest rate of non-diagnostic results and lower radiation exposure than CTPA 3
• Normal perfusion scan rules out PE without further testing 3

Compression Ultrasonography

Consider compression ultrasonography in patients with clinical signs of DVT or as an adjunct in high probability patients with negative CTPA. 1, 4, 3

• Finding proximal DVT is sufficient to warrant anticoagulation without further PE imaging 3
• Color Doppler imaging is the investigation of choice for suspected lower limb DVT 1

Special Populations

Hemodynamically Unstable Patients

Perform immediate bedside transthoracic echocardiography to assess for right ventricular dysfunction. 3

• Echocardiographic findings of RV dysfunction, RV dilatation, pulmonary artery enlargement, and tricuspid regurgitation can justify emergency reperfusion therapy without further testing 1, 3
• If patient can be stabilized, proceed directly to CTPA without D-dimer testing 3

Hospitalized Patients

D-dimer specificity is lower in inpatients due to comorbidities, but testing remains appropriate as sensitivity stays high. 2

• Consider proceeding more directly to imaging rather than relying heavily on D-dimer in hospitalized patients 3
• A normal D-dimer with appropriate pretest stratification still prevents unnecessary imaging 2

Pregnant Patients

Consider lower-extremity venous ultrasonography before CT to reduce radiation exposure, especially in first trimester. 2

• Refer to pregnancy-specific PE diagnostic algorithms as standard D-dimer thresholds and radiation considerations differ 3

Common Pitfalls to Avoid

• Never apply PERC to patients >50 years old, as age <50 is a required criterion 2
• Never use standard 500 ng/mL D-dimer cutoff in patients >50 years, as this leads to unnecessary imaging due to poor specificity 2
• Never order D-dimer in high pretest probability patients—proceed directly to imaging 2, 3
• Never skip pretest probability assessment, as D-dimer and imaging interpretation depend critically on it 3
• Never use point-of-care D-dimer assays when laboratory-based tests are available, as they have lower sensitivity (88% vs. 95%) 2