What is the recommended test for ruling out a pulmonary embolus (blood clot in the lungs)?

From the Guidelines

The recommended test for ruling out a pulmonary embolism (PE) is a CT pulmonary angiogram (CTPA), which is considered the gold standard diagnostic test. This imaging study involves injecting contrast material into the bloodstream and using computed tomography to create detailed images of the pulmonary arteries. Before proceeding to CTPA, clinicians typically assess the patient's clinical probability of PE using validated tools like the Wells score or Geneva score, followed by a D-dimer blood test in patients with low or intermediate probability 1. A negative D-dimer in low-risk patients can effectively rule out PE without further imaging. For patients with contraindications to CTPA (such as severe kidney disease or contrast allergy), a ventilation-perfusion (V/Q) scan is an alternative option. In some cases, lower extremity ultrasound may be performed to look for deep vein thrombosis, which is often the source of pulmonary emboli. The diagnostic approach should be tailored to the individual patient, considering their clinical presentation, risk factors, and contraindications to specific tests.

Key Considerations

• The Pulmonary Embolism Rule-Out Criteria (PERC) can be used to identify low-risk patients in whom the risks of any testing, including a plasma d-dimer level, outweigh the risk for PE 1.
• Age-adjusted d-dimer thresholds (age × 10 ng/mL) can 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.
• CTPA is the preferred imaging modality for patients with high pretest probability of PE, while ventilation-perfusion scans can be used as an alternative in patients with contraindications to CTPA 1.

Diagnostic Approach

• For patients with low pretest probability of PE, apply the PERC criteria and consider a plasma d-dimer test if the criteria are not met 1.
• For patients with intermediate pretest probability of PE, a normal plasma d-dimer level provides sufficient negative predictive value for PE, while an elevated level should prompt imaging studies 1.
• For patients with high pretest probability of PE, imaging studies should be performed, with CTPA being the preferred modality 1.

From the Research

Diagnostic Tests for Pulmonary Embolus

The recommended test for ruling out a pulmonary embolus (blood clot in the lungs) is:

• Computed Tomography Pulmonary Angiography (CTPA) 2, 3, 4, 5

Characteristics of CTPA

CTPA has been shown to have:

• High sensitivity and specificity for the diagnosis of pulmonary embolism 2
• The ability to determine the presence or absence of pulmonary embolism with sufficient certainty without the need for additional imaging tests after a negative CTPA 2
• Emerging as the imaging test of first choice 2

Alternative Diagnostic Tests

Alternative tests include:

• Ventilation-perfusion (V/Q) scanning, which may be preferred in some patient populations 3
• Compression ultrasonography, reserved for patients with concomitant symptomatic deep vein thrombosis 2
• Magnetic resonance pulmonary angiography, which is not currently a suitable alternative for CTPA 2

Clinical Considerations

When using CTPA to rule out pulmonary embolism:

• A negative CTPA result can essentially rule out the diagnosis of pulmonary embolism without the need to routinely exclude the presence of deep vein thrombosis 3
• Clinical outcome studies have demonstrated that pulmonary embolism can be safely ruled out in patients with a clinical probability indicating pulmonary embolism to be unlikely and a normal D-dimer test result 2