From the Guidelines
The first investigation to be done in suspected pulmonary embolism is a D-dimer blood test, particularly in patients with low to intermediate clinical probability of PE. This approach is supported by the most recent guidelines, including those from the European Society of Cardiology (ESC) and the American College of Physicians (ACP) 1. 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 probability can effectively rule out pulmonary embolism 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, or after surgery.
Key Considerations
- Before ordering tests, clinicians should assess the patient's clinical probability using validated tools like the Wells score or Geneva score to guide the diagnostic approach 1.
- If the D-dimer is positive or if the patient has a high clinical probability of PE, the next step would be imaging studies, typically a CT pulmonary angiogram (CTPA) 1.
- Age-adjusted d-dimer thresholds should be used in patients older than 50 years to determine whether imaging is warranted 1.
- Clinicians should not obtain any imaging studies in patients with a d-dimer level below the age-adjusted cutoff 1.
Diagnostic Approach
- The strategy of combining clinical probability assessment with selective D-dimer testing helps avoid unnecessary radiation exposure while ensuring that potentially life-threatening pulmonary emboli are not missed 1.
- CTPA is the method of choice for imaging the pulmonary vasculature in patients with suspected PE, especially when the clinical probability is high or when D-dimer testing is positive 1.
From the Research
Diagnostic Approaches for Pulmonary Embolism
The first investigation to be done in pulmonary embolism is often a topic of discussion among medical professionals.
- Computed Tomography Pulmonary Angiography (CTPA) is considered a reliable test for the diagnosis of pulmonary embolism 2, 3, 4, 5.
- CTPA has been shown to have a high sensitivity and specificity for the diagnosis of pulmonary embolism, making it a suitable first-line investigation 4.
- Ventilation-perfusion (V/Q) scanning is another diagnostic approach, but its use has been largely replaced by CTPA in many centers due to concerns about its low sensitivity 2.
- The choice of initial investigation may depend on various factors, including patient population, clinical presentation, and availability of resources 3.
Comparison of Diagnostic Tests
- Studies have compared the diagnostic accuracy of CTPA and V/Q scanning, with CTPA being found to be more sensitive and reliable 2, 3.
- CTPA has been associated with a higher incidence of diagnosed pulmonary embolism, but its use also raises concerns about radiation exposure, particularly in young women 3.
- Alternative diagnostic approaches, such as single photon emission tomography (SPECT) V/Q and modified diagnostic criteria for V/Q scan interpretation, may offer safer alternatives to CTPA in certain patient populations 3.
Clinical Guidelines and Recommendations
- Clinical outcome studies have demonstrated that pulmonary embolism can be safely ruled out in patients with a low clinical probability and a normal D-dimer test result, obviating the need for additional radiological imaging tests 4.
- CTPA is generally considered the imaging test of first choice for diagnosing pulmonary embolism, with compression ultrasonography and ventilation-perfusion scintigraphy reserved for specific cases 4.