What is the diagnostic approach for pulmonary embolism (PE)?

Diagnostic Approach for Pulmonary Embolism

The diagnosis of pulmonary embolism (PE) requires a structured approach using clinical probability assessment, D-dimer testing, and appropriate imaging studies, as PE cannot be accurately diagnosed based on signs, symptoms, and history alone. 1

Initial Risk Stratification

• Begin with clinical probability assessment using either validated prediction rules or clinical gestalt to categorize patients into low, intermediate, or high probability of PE 1
• For patients with suspected high-risk PE (presenting with shock or hypotension), echocardiography is the most useful initial test to detect signs of right ventricular overload 1
• In hemodynamically stable patients (non-high-risk PE), use structured assessment tools like Wells score or clinical judgment to determine pre-test probability 1

Low Clinical Probability Patients

• Apply the Pulmonary Embolism Rule-Out Criteria (PERC) for patients with low clinical probability 1
• If all 8 PERC criteria are met (age <50 years, heart rate <100/min, oxygen saturation >94%, no recent surgery/trauma, no prior VTE, no hemoptysis, no unilateral leg swelling, no estrogen use), no further testing is needed 1, 2
• If PERC criteria are not all met, proceed to D-dimer testing 1
• A normal D-dimer level (<500 ng/mL) in low-risk patients safely excludes PE without need for imaging 1
• For patients >50 years, consider age-adjusted D-dimer cutoff (age × 10 ng/mL) to improve specificity while maintaining sensitivity 1
• If D-dimer is elevated, proceed to imaging studies 1

Intermediate Clinical Probability Patients

• Order D-dimer testing for all patients with intermediate pre-test probability 1
• A normal D-dimer level excludes PE without need for further imaging 1
• If D-dimer is elevated, proceed to imaging studies 1

High Clinical Probability Patients

• D-dimer testing is not recommended in high clinical probability patients as a normal result does not safely exclude PE 1
• Proceed directly to imaging studies 1

Imaging Studies

• CT pulmonary angiography (CTPA) is the preferred imaging modality for diagnosing PE when available and not contraindicated 1
• Ventilation-perfusion (V/Q) lung scanning is an alternative when CTPA is contraindicated (contrast allergy, renal dysfunction) or unavailable 1
• A normal perfusion scan excludes PE 1
• A high-probability V/Q scan confirms PE in patients with high clinical probability 1
• Lower-limb compression ultrasonography (CUS) can be considered in selected patients to detect deep vein thrombosis (DVT), as finding a proximal DVT confirms PE 1
• Echocardiography is not recommended for routine diagnosis in hemodynamically stable patients but is valuable for risk stratification 1

Special Scenarios

• For suspected high-risk PE with shock or hypotension where CT is not immediately available, bedside echocardiography showing right ventricular overload may justify PE-specific treatment 1
• In pregnant patients, consider V/Q scanning to reduce radiation exposure to the fetus if chest X-ray is normal 1
• For patients with renal failure, consider V/Q scanning instead of CTPA to avoid contrast-induced nephropathy 1

Common Pitfalls and Caveats

• PE symptoms are nonspecific and may be confused with other cardiopulmonary disorders, leading to underdiagnosis 3, 4
• Failure to follow evidence-based diagnostic strategies when withholding anticoagulation despite clinical suspicion of PE is associated with increased VTE episodes and sudden death 1
• Relying solely on clinical features without appropriate diagnostic testing is inadequate for definitive diagnosis or exclusion of PE 3
• Overuse of CT imaging has led to increased diagnosis of less severe PEs without clear mortality benefit, while exposing patients to radiation and contrast risks 1
• Repeated imaging is common - approximately one-third of ED patients who had CT for PE evaluation underwent another CT for the same reason within 5 years 1

By following this structured diagnostic approach, clinicians can accurately diagnose or exclude PE while minimizing unnecessary testing and radiation exposure.