From the Guidelines
The first-line diagnostic test to rule out pulmonary embolism (PE) is the D-dimer blood test, particularly in patients with low to intermediate clinical probability of PE. This recommendation is based on the guidelines from the American College of Physicians, as outlined in the study by 1, which suggests that a high-sensitivity D-dimer measurement should be obtained as the initial diagnostic test in patients with intermediate pretest probability of PE or in patients with low pretest probability of PE who do not meet all Pulmonary Embolism Rule-Out Criteria.
The D-dimer test measures fibrin degradation products that are elevated when blood clots are being actively broken down in the body. A negative D-dimer test in a patient with low clinical suspicion can effectively rule out PE without the need for further imaging. However, D-dimer has high sensitivity but low specificity, meaning false positives are common, especially in elderly patients, pregnant women, those with cancer, recent surgery, or inflammation.
If the D-dimer is positive or if the patient has high clinical probability of PE, imaging studies such as CT pulmonary angiography (CTPA) should follow, as recommended by 1. Clinical probability assessment using validated tools like the Wells score or PERC rule should precede D-dimer testing to determine the appropriate diagnostic pathway. This approach minimizes unnecessary radiation exposure while ensuring that potentially life-threatening PEs are not missed.
Some key points to consider when using the D-dimer test include:
- Using age-adjusted D-dimer thresholds (age × 10 ng/mL) in patients older than 50 years to determine whether imaging is warranted, as suggested by 1.
- Not obtaining any imaging studies in patients with a D-dimer level below the age-adjusted cutoff, as recommended by 1.
- Reserving imaging with CTPA for patients with high pretest probability of PE, as suggested by 1 and 1.
Overall, the D-dimer test is a useful initial diagnostic tool for ruling out PE in patients with low to intermediate clinical probability, and its use should be guided by clinical probability assessment and age-adjusted thresholds.
From the Research
Diagnostic Tests for Pulmonary Embolism (PE)
To rule out pulmonary embolism (PE), the following diagnostic tests can be considered:
- Computed Tomography Pulmonary Angiography (CTPA) is the most commonly used and reliable test for diagnosing PE, as it provides accurate images of the pulmonary arteries and can detect blood clots 2, 3, 4, 5.
- Ventilation-Perfusion (V/Q) scan is an alternative test that can be used, especially in patients with contraindications to CTPA, but it has lower sensitivity and specificity compared to CTPA 4, 6.
- Magnetic Resonance Imaging (MRI) and Magnetic Resonance Pulmonary Angiography are not commonly used for diagnosing PE due to limited availability and higher levels of expertise required 3, 5.
- Compression ultrasonography can be used to diagnose deep vein thrombosis (DVT), which is often associated with PE, but it is not a primary test for diagnosing PE 3.
- D-dimer test can be used as a screening test to rule out PE, but it has low specificity and requires confirmation with imaging tests like CTPA 3, 4.
First-Line Diagnostic Test
The first-line diagnostic test to rule out PE is Computed Tomography Pulmonary Angiography (CTPA), due to its high sensitivity and specificity, and ability to provide rapid turnaround time 2, 3, 5. CTPA can detect blood clots in the pulmonary arteries and provide information on other potential causes of acute chest pain. However, it is essential to consider the patient's clinical probability of PE, medical history, and potential contraindications to CTPA before ordering the test 3, 4.