What is the diagnostic protocol for suspected pulmonary embolism (PE)?

Diagnostic Protocol for Pulmonary Embolism

Initial Risk Stratification

Begin by assessing pretest probability using either validated clinical decision rules (Wells score, revised Geneva score) or clinical gestalt—both are acceptable, though gestalt may outperform structured scores in experienced hands. 1, 2

Clinical Probability Assessment Tools

• Wells Score: Assigns points for clinical signs of DVT (3 points), PE more likely than alternative diagnosis (3 points), heart rate >100 bpm (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). Score ≤4 = PE unlikely; >4 = PE likely 1

• Revised Geneva Score: Uses age >65 years (1 point), previous DVT/PE (3 points), surgery/fracture within 1 month (2 points), active malignancy (2 points), unilateral leg pain (3 points), hemoptysis (2 points), heart rate 75-94 bpm (3 points) or ≥95 bpm (5 points), and unilateral edema with deep vein tenderness (4 points). Score 0-3 = low probability (8% PE prevalence); 4-10 = intermediate (28%); ≥11 = high (74%) 3

• Clinical gestalt may achieve better discrimination than structured scores (AUC 0.81 vs 0.71 for Wells and 0.66 for Geneva), particularly for identifying truly low-risk (7.6% PE prevalence) and high-risk patients (72.1% prevalence) 2

Hemodynamically Unstable Patients (High-Risk PE)

For patients presenting with shock or sustained hypotension (systolic BP <90 mmHg for ≥15 minutes), perform immediate bedside transthoracic echocardiography to assess for right ventricular dysfunction. 1

• If RV dysfunction is present and the patient is critically unstable, echocardiographic findings alone justify emergency reperfusion therapy without further testing 1

• If the patient can be stabilized, proceed directly to CT pulmonary angiography (CTPA) without D-dimer testing 1

• Ancillary bedside tests include transesophageal echocardiography (may visualize thrombi in main pulmonary arteries) and bilateral compression ultrasound (positive DVT confirms venous thromboembolism) 1

Hemodynamically Stable Patients

Low Pretest Probability

For patients with low clinical probability, apply the Pulmonary Embolism Rule-Out Criteria (PERC) before ordering any tests. 1

PERC Criteria (all 8 must be met to rule out PE):

• Age <50 years

• Heart rate <100 bpm

• Oxygen saturation ≥95% on room air

• No hemoptysis

• No estrogen use

• No prior DVT/PE

• No unilateral leg swelling

• No surgery/trauma requiring hospitalization within 4 weeks 1

• If all 8 PERC criteria are met, PE is ruled out—do not order D-dimer or imaging (pooled sensitivity 97%, missed PE rate only 0.3%) 1

• If any PERC criterion is not met, proceed to D-dimer testing 1

D-Dimer Testing in Low Probability Patients

• Use age-adjusted D-dimer cutoffs for patients >50 years (age × 10 ng/mL) rather than the standard 500 ng/mL threshold—this maintains >97% sensitivity while significantly improving specificity 1

• If D-dimer is negative (below age-adjusted or standard threshold), PE is excluded—no imaging needed 1

• If D-dimer is positive, proceed to CTPA 1

Intermediate Pretest Probability

For intermediate-risk patients, proceed directly to D-dimer testing (PERC is not validated for this group). 1

• Use age-adjusted D-dimer cutoffs (age × 10 ng/mL for patients >50 years) 1

• If D-dimer is negative, PE is excluded—no imaging required 1

• If D-dimer is positive, proceed to CTPA 1

Alternative: YEARS Algorithm

• The YEARS algorithm offers an alternative approach: assess for 3 clinical items (signs of DVT, hemoptysis, PE most likely diagnosis) 1

• PE is excluded if: no clinical items present AND D-dimer <1000 ng/mL, OR ≥1 clinical item present AND D-dimer <500 ng/mL 1

• This approach safely avoided CTPA in 48% of patients vs 34% with standard Wells/D-dimer strategy, with only 0.61% VTE rate at 3 months 1

High Pretest Probability

For high-risk patients, proceed directly to CTPA without D-dimer testing—a negative D-dimer cannot safely exclude PE when pretest probability is high (negative predictive value only 60%). 1

Imaging Studies

CT Pulmonary Angiography (CTPA)

CTPA is the preferred imaging modality for PE diagnosis with sensitivity 83% and specificity 96% 1

• A negative CTPA in low or intermediate probability patients effectively rules out PE (negative predictive value 96% and 89% respectively) 1

• In high probability patients with negative CTPA, consider additional testing (negative predictive value only 60% in this group) 1

• CTPA visualizes pulmonary arteries to subsegmental level and may provide alternative diagnoses 1

• Radiation effective dose is 3-10 mSv with significant breast tissue exposure in young women 1

Ventilation-Perfusion (V/Q) Scanning

Use V/Q scanning when CTPA is contraindicated (iodine allergy, renal insufficiency, pregnancy concerns) or unavailable 1

• V/Q SPECT has lowest rate of non-diagnostic results (<3%) compared to planar V/Q (50% inconclusive) 1

• Lower radiation than CTPA (effective dose 2 mSv) 1

• Cannot provide alternative diagnosis if PE is excluded 1

Compression Ultrasound

Consider lower extremity compression ultrasound as initial test in patients with obvious clinical signs of DVT—a positive result confirms venous thromboembolism and justifies anticoagulation without pulmonary imaging 1, 4

• Approximately 50% of patients with proven PE have detectable proximal DVT 1

• A negative ultrasound does not rule out PE and requires pulmonary imaging 1

Special Populations

Hospitalized Patients

D-dimer has severely limited utility in hospitalized patients due to high false-positive rates from surgery, infection, inflammation, and malignancy—fewer than 10% will have negative D-dimer regardless of PE status 1

• In hospitalized patients with suspected PE, proceed more directly to imaging rather than relying on D-dimer 1

Pregnant Patients

Refer to dedicated pregnancy-specific PE diagnostic algorithms—standard D-dimer thresholds and radiation considerations differ 1

Critical Pitfalls to Avoid

• Never use positive D-dimer alone to diagnose PE—confirmation with imaging is mandatory (D-dimer specificity only 35%) 5, 4

• Never order D-dimer in high probability patients—proceed directly to imaging 1

• Do not skip pretest probability assessment—D-dimer and imaging interpretation depend critically on pretest probability 1

• Avoid CTPA overuse in truly low-risk patients—apply PERC criteria rigorously to prevent unnecessary testing 1

• Do not use point-of-care D-dimer assays except in low probability patients—they have lower sensitivity (88% vs ≥95% for laboratory assays) 1

• In patients >50 years, use age-adjusted D-dimer cutoffs—standard 500 ng/mL threshold causes excessive false positives in elderly patients 1