From the Guidelines
The best initial diagnostic test for suspected pulmonary embolism (PE) is a high-sensitivity D-dimer measurement, combined with clinical probability assessment using validated tools, as recommended by the American College of Physicians 1. This approach allows for the safe exclusion of PE in patients with low clinical probability and negative D-dimer results. For patients with high clinical probability or positive D-dimer results, CT pulmonary angiography (CTPA) is the gold standard diagnostic test, as it directly visualizes the pulmonary arterial tree and can detect filling defects caused by emboli with high sensitivity and specificity 2. The diagnostic approach should be tailored to the individual patient's risk factors, clinical presentation, and contraindications to specific tests, with the goal of balancing diagnostic accuracy with minimizing unnecessary radiation and contrast exposure. Some key considerations include:
- Using age-adjusted D-dimer thresholds in patients older than 50 years to determine whether imaging is warranted 1
- Reserving ventilation-perfusion scans for patients who have a contraindication to CTPA or if CTPA is not available 1
- Avoiding imaging tests in patients with a D-dimer level below the age-adjusted cutoff 1
- Considering alternative diagnostic strategies, such as compression ultrasonography of the legs, in specific populations, such as pregnant patients.
From the Research
Diagnostic Tests for Pulmonary Embolism
The best diagnostic test for suspected pulmonary embolism (PE) is computed tomography pulmonary angiography (CTPA) due to its high sensitivity and specificity for the diagnosis of PE 3, 4, 5, 6.
Characteristics of CTPA
- CTPA is the imaging test of first choice for diagnosing PE 3
- It has a high sensitivity and specificity for the diagnosis of PE 3, 4
- A negative CTPA result can essentially rule out the diagnosis of PE without the need for additional imaging tests 3, 4, 5
- CTPA is considered the gold standard diagnostic technique in patients with suspected acute PE in emergency departments 6
Alternative Diagnostic Tests
- Ventilation-perfusion (V/Q) scanning is an alternative diagnostic test for PE, but it has a lower sensitivity and specificity compared to CTPA 4, 7
- Compression ultrasonography is reserved for patients with concomitant symptomatic deep vein thrombosis 3
- Magnetic resonance pulmonary angiography is not a suitable alternative for CTPA 3
- Single photon emission tomography (SPECT) V/Q and modified diagnostic criteria for V/Q scan interpretation can increase diagnostic accuracy compared to V/Q scanning 4
Considerations for Diagnostic Testing
- The choice of initial diagnostic test should be guided by clinical assessment of the probability of PE and patient characteristics that may influence test accuracy 7
- Diagnostic algorithms using either CTPA or V/Q scanning have proven to be comparably safe to exclude the diagnosis of PE 4
- Excluding low-risk patients for PE as defined by clinical scoring systems and D-dimer testing would enhance the yield of diagnostic testing 4