What is the recommended workup for a suspected pulmonary embolism (PE)?

Workup of Suspected Pulmonary Embolism

Begin with clinical probability assessment, then use D-dimer testing in low-to-intermediate risk patients to exclude PE, reserving CT pulmonary angiography (CTPA) as the definitive imaging modality for those with elevated D-dimer or high clinical probability. 1

Initial Assessment: Clinical Probability Stratification

• All patients must have their clinical probability assessed and documented using validated tools (such as Wells score or Geneva score) before any testing. 1
• Always consider alternative diagnoses at presentation, as many conditions mimic PE. 1
• Start anticoagulation immediately in patients with intermediate or high clinical probability while awaiting imaging, as this reduces mortality. 1

D-Dimer Testing Strategy

• Perform D-dimer testing only after clinical probability assessment—never order it reflexively. 1
• Do not perform D-dimer in high clinical probability patients because the negative predictive value is too low in this population. 1
• A negative D-dimer reliably excludes PE in low and intermediate clinical probability patients—no imaging is needed. 1
• Use age-adjusted D-dimer thresholds for patients over 50 years (age × 10 ng/mL for those >50 years) to improve specificity while maintaining sensitivity >97%. 1
• D-dimer is less useful in hospitalized patients due to high false-positive rates. 1

Imaging: The Definitive Diagnostic Step

CT Pulmonary Angiography (CTPA)

• CTPA is the recommended initial imaging modality for non-massive PE and has become the de facto gold standard. 1
• A good quality negative CTPA excludes PE—no further investigation or treatment is required. 1
• CTPA should be performed within 24 hours for non-massive PE and within 1 hour for massive PE. 1
• CTPA is the second-line test after elevated D-dimer and the first-line test in high clinical probability patients. 1

Alternative Imaging Modalities

Lower Extremity Compression Ultrasonography (CUS):

• Finding proximal DVT in a patient with suspected PE is sufficient to start anticoagulation without further testing. 1
• CUS is particularly useful before CTPA in patients with contraindications to CT (renal failure, contrast allergy, pregnancy, or lower extremity symptoms). 1
• CUS shows DVT in 30-50% of patients with PE. 1
• A single negative ultrasound should not be relied upon to exclude subclinical DVT. 1

Ventilation-Perfusion (V/Q) Scanning:

• V/Q scanning may be considered when: (a) facilities are available on-site, (b) chest X-ray is normal, (c) no significant concurrent cardiopulmonary disease exists, and (d) standardized reporting is used. 1
• V/Q scanning is preferred over CT in younger patients and pregnant women to minimize radiation exposure, particularly breast tissue radiation. 1
• A normal V/Q scan reliably excludes PE, but high-probability results have significant false positives. 1
• V/Q scanning is diagnostic in only 30-50% of cases; non-diagnostic results require further imaging. 1

Massive PE: Emergent Workup

• In patients presenting with shock or hypotension, perform CTPA or echocardiography immediately to diagnose massive PE. 1
• Thrombolysis may be instituted on clinical grounds alone if cardiac arrest is imminent—do not delay for imaging. 1
• Imaging should be performed within 1 hour in massive PE. 1

Common Pitfalls and Special Considerations

Avoid Over-Testing:

• Do not perform CTPA as a first-line test without clinical probability assessment and D-dimer—this leads to overdiagnosis and unnecessary radiation exposure. 1
• In patients with multiple prior CTs for PE, consider lower extremity ultrasound or V/Q scanning to reduce cumulative radiation exposure. 1

Pregnancy:

• In pregnant patients with lower extremity symptoms, start with compression ultrasonography to avoid fetal radiation exposure. 1
• If imaging is necessary, weigh risks carefully; CT exposes the fetus to less radiation than V/Q scanning but may have teratogenic effects. 1

Hospitalized Patients:

• D-dimer has limited utility in hospitalized patients due to high false-positive rates from comorbidities. 1
• Consider proceeding directly to CTPA in hospitalized patients with intermediate-to-high clinical probability. 1

Additional Workup After PE Diagnosis

• Testing for thrombophilia should be considered only in patients under 50 with recurrent PE or strong family history of VTE. 1
• Investigations for occult cancer are indicated only when clinically suspected or abnormal on routine blood tests/chest X-ray—not routinely. 1
• 7-12% of patients with idiopathic VTE have unrecognized cancer detectable by clinical assessment, routine labs, and chest X-ray. 1