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Diagnosis of Pulmonary Embolism
Study Questions:
What is the safety and efficacy of a D-dimer threshold for diagnoses of pulmonary embolism (PE) based on clinical probability?
Methods:
The authors performed a prospective study comparing two D-dimer thresholds for ruling out PE. For patients with low pretest probability based on the Wells score (0-4.0), a D-dimer threshold of 1000 ng/ml was used to rule out acute PE. For patients with a moderate pretest probability based on the Wells score (4.5-6.0), a D-dimer threshold of 500 ng/ml was used to rule out acute PE. All patients who did not rule out acute PE (either high pretest probability or elevated D-dimer level) underwent chest imaging. All patients were followed for 3 months to detect any new diagnosis of venous thromboembolism (VTE).
Results:
Of 2,017 patients enrolled and evaluated, 7.4% had acute PE diagnosed on initial imaging. Of 1,325 patients with low (n = 1,285) or moderate (n = 40) pretest probability and a negative D-dimer test, none developed VTE during follow-up (95% confidence interval [CI], 0-0.29%). This included 315 patients with low pretest probability and a D-dimer level between 500-900 ng/ml. This diagnostic strategy resulted in the use of chest imaging in 34.3% of patients compared to 51.9% of patients if a standard D-dimer threshold of 500 ng/ml were used for all patients (difference, 17.6%; 95% CI, 15.9%-19.2%).
Conclusions:
The authors concluded that the use of a higher D-dimer threshold (1000 ng/ml) for patients at low pretest probability for acute PE was safe and reduced the overall number of chest imaging procedures.
Perspective:
While the Wells score is commonly used to assess the pretest probability for acute PE, most clinicians use the same D-dimer threshold for rule out testing across the pretest probability range. As compared to some other studies exploring the use of an age-adjusted D-dimer threshold (usually age x 100 for age 50+ years), this study used two different D-dimer thresholds. Doing so proved safe and significantly reduced the number of chest imaging procedures (e.g., CT pulmonary angiography). Emergency department providers should consider methods to standardize diagnostic strategies that employ some form of variable D-dimer threshold based either on age or pretest probability in an effort to reduce unnecessary imaging testing.
Keywords: Angiography, Anticoagulants, Diagnostic Imaging, Emergency Service, Hospital, Fibrin Fibrinogen Degradation Products, Pulmonary Embolism, Secondary Prevention, Tomography, X-Ray Computed, Vascular Diseases, Venous Thromboembolism
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