What are the diagnostic criteria and treatment options for pulmonary embolism?

Diagnostic Criteria for Pulmonary Embolism

The diagnosis of pulmonary embolism requires a structured, sequential approach based on clinical probability assessment, D-dimer testing in appropriate patients, and confirmatory imaging with CT pulmonary angiography (CTPA) as the preferred modality. 1

Initial Clinical Assessment and Risk Stratification

Determine hemodynamic stability first—this dictates your entire diagnostic pathway. 2

• High-risk PE (hemodynamically unstable): Defined by shock or systolic blood pressure <90 mmHg; requires immediate bedside echocardiography if CT is unavailable, and treatment should not be delayed for imaging 2
• Non-high-risk PE (hemodynamically stable): Proceed with structured clinical probability assessment using validated tools like Wells score or structured clinical judgment 3, 2

The European Society of Cardiology recommends either a three-level scheme (low, intermediate, high probability) or two-level scheme (PE unlikely vs. PE likely) for clinical probability assessment 2

D-Dimer Testing Strategy

Only measure D-dimer in patients with low or intermediate clinical probability, or those classified as "PE unlikely"—never order it in high clinical probability patients. 2

• A negative D-dimer (<500 ng/mL) in low/intermediate probability patients safely excludes PE without further testing, with 3-month thromboembolic risk below 1% 4, 3, 2
• Consider age-adjusted cutoffs (age × 10 ng/mL in patients >50 years) to improve specificity 4
• If D-dimer is elevated, proceed directly to imaging 3, 2

Special Rule-Out Criteria

Apply the Pulmonary Embolism Rule-Out Criteria (PERC) in patients with low clinical probability—if all 8 PERC criteria are met, no further testing is needed 3

Imaging Modalities for Confirmation

CT Pulmonary Angiography (First-Line)

CTPA is the imaging test of first choice and should be performed in patients with elevated D-dimer or high clinical probability. 3, 2

• Accept the diagnosis of PE if CTPA shows a segmental or more proximal filling defect 1, 2
• A normal multidetector CT (MDCT) alone safely excludes PE in patients with non-high clinical probability 1
• Single-detector CT (SDCT) requires additional compression ultrasonography (CUS) of lower extremities due to lower sensitivity 1
• Reject the diagnosis without further testing if CTPA is normal in patients with low or intermediate clinical probability 4

Ventilation-Perfusion (V/Q) Scintigraphy (Alternative)

V/Q scanning is a valid option when CTPA is contraindicated (renal failure, contrast allergy, pregnancy with normal chest X-ray) 1, 3

• A normal perfusion scan definitively excludes PE without further testing 4, 2
• A high-probability V/Q scan confirms PE in patients with high clinical probability 1, 3
• Non-diagnostic scans (low or intermediate probability) combined with low clinical probability and negative proximal CUS can exclude PE 1

Compression Ultrasonography

Finding a proximal deep vein thrombosis (DVT) on CUS is sufficient to warrant anticoagulation without further testing for PE 1

• CUS shows DVT in 30-50% of patients with PE 1
• Particularly useful before CT in patients with contraindications to contrast (renal failure, allergy) to potentially avoid CT altogether 1
• Mandatory when using single-detector CT due to its lower sensitivity 1

Pulmonary Angiography (Gold Standard)

Pulmonary angiography remains the reference standard but should be reserved for patients in whom non-invasive tests remain indeterminate 1

• Direct angiographic signs include complete vessel obstruction with concave border or filling defect 1
• Sensitivity and specificity both range from 95-98% 1

Validated Diagnostic Criteria Summary

For excluding PE (no further testing required): 1

• Normal pulmonary angiogram
• Negative highly sensitive D-dimer assay in low/intermediate probability patients
• Normal perfusion lung scan
• Normal MDCT alone in non-high clinical probability patients
• Normal SDCT plus negative proximal CUS

For confirming PE (treatment warranted): 1

• Pulmonary angiogram showing PE
• High-probability V/Q scan
• Proximal DVT on CUS
• MDCT or SDCT showing PE at least at segmental level

Post-Diagnosis Risk Stratification

All patients with confirmed PE must be stratified by hemodynamic stability to identify high-risk patients with elevated early mortality. 4

• Assess right ventricular function via imaging or biomarkers even in patients with low PESI/sPESI scores, as RV dysfunction affects early prognosis 4
• The presence of proximal DVT on CUS increases risk of recurrent VTE in PE patients 1

Critical Pitfalls to Avoid

Failure to follow evidence-based diagnostic strategies when withholding anticoagulation despite clinical suspicion is associated with significantly increased VTE episodes and sudden death. 3

• Never measure D-dimer in high clinical probability patients—it wastes time and can be falsely reassuring 2
• Do not use MR angiography to rule out PE—it is not validated for this purpose 2
• Avoid CT venography as an adjunct to CTPA—it adds no diagnostic value 2
• Subsegmental PE on CT remains controversial and may require additional testing for confirmation 1
• 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 3