What is the recommended diagnostic test for a patient who develops pulmonary emboli?

Diagnostic Testing for Suspected Pulmonary Embolism

CT pulmonary angiography (CTPA) is the recommended first-line diagnostic test for patients with suspected pulmonary embolism, as it has excellent accuracy and can definitively confirm or exclude PE without further testing in most cases. 1

Initial Clinical Assessment

Before ordering imaging, assess clinical probability using validated prediction rules (such as Wells score or Geneva score) and measure D-dimer levels in appropriate patients 1:

• In patients with low or intermediate clinical probability ("PE-unlikely"): Measure D-dimer first using a highly sensitive assay 1

  • If D-dimer is negative (using standard cut-off, age-adjusted cut-off >50 years: age × 10 μg/L, or probability-adjusted cut-off), PE is excluded without imaging 1
  • If D-dimer is positive, proceed to CTPA 1

• In patients with high clinical probability ("PE-likely"): Do not measure D-dimer, as a normal result does not safely exclude PE—proceed directly to CTPA 1

Primary Diagnostic Test: CTPA

CTPA should be performed as the definitive imaging test 1:

• Sensitivity of 83% and specificity of 96% for PE diagnosis 2
• Low rate of inconclusive results (3-5%) compared to other modalities 1
• Can provide alternative diagnoses when PE is excluded 1, 3
• Available 24 hours in most centers 2, 3

CTPA Interpretation Guidelines

• Accept PE diagnosis without further testing if CTPA shows segmental or more proximal filling defect in patients with intermediate or high clinical probability 1
• Reject PE diagnosis without further testing if CTPA is normal in patients with low or intermediate clinical probability 1
• Consider rejecting PE diagnosis if CTPA is normal even in high clinical probability patients 1
• Consider further imaging only for isolated subsegmental filling defects 1

CTPA Contraindications and Limitations

• Severe renal failure (contrast nephropathy risk) 1
• Contrast allergy 2
• Pregnancy concerns (radiation exposure to breast tissue, though still can be used when clinically indicated) 1
• Radiation exposure: effective dose 3-10 mSv 2

Alternative Diagnostic Tests

Ventilation-Perfusion (V/Q) Scintigraphy

Use V/Q scanning when CTPA is contraindicated 1:

• Lower radiation than CTPA (effective dose ~2 mSv) 1
• Almost no contraindications 1
• Reject PE diagnosis if perfusion scan is normal 1
• Consider accepting PE diagnosis if V/Q scan shows high probability for PE 1
• Major limitation: inconclusive in 50% of cases with planar imaging 1
• V/Q SPECT reduces non-diagnostic rate to <3% but lacks validation in prospective management studies 1

Lower-Limb Compression Ultrasonography (CUS)

Accept PE diagnosis if CUS shows proximal DVT in a patient with clinical suspicion of PE 1:

• High specificity (96%) but low sensitivity (41%) for PE 1
• Most useful in patients with leg symptoms suggesting DVT 1
• If only distal DVT is found, further testing should be considered to confirm PE 1
• If positive proximal CUS is used to confirm PE, assess PE severity for risk-adjusted management 1

Tests NOT Recommended

• CT venography as adjunct to CTPA: Not recommended 1
• Magnetic resonance angiography (MRA): Not recommended for ruling out PE 1
• Pulmonary angiography: Invasive with highest radiation (10-20 mSv), reserved only for cases where non-invasive tests remain indeterminate 1

Special Situation: Hemodynamically Unstable Patients (High-Risk PE)

In patients with shock or hypotension 1:

• Perform bedside echocardiography if CT is not immediately available or patient is too unstable to transport 1
• Initiate IV anticoagulation with unfractionated heparin (including weight-adjusted bolus) without delay while diagnostic workup proceeds 1
• Accept PE diagnosis based on echocardiographic findings of RV overload if other tests unavailable and patient critically unstable 1
• Confirm with CTPA once patient stabilized 1

Critical Pitfalls to Avoid

• Do not order D-dimer in high clinical probability patients—it will not safely exclude PE even if normal 1
• Do not routinely perform lower extremity ultrasound after negative multidetector CTPA—it is unnecessary 4, 5
• Do not dismiss subsegmental PE findings—consider clinical context and further testing if isolated 1
• Do not use clinical judgment alone after non-diagnostic tests—this approach increases VTE episodes and sudden death 1