Background: Plasma D-dimer measurement is used in the assessment of the clinical probability of pulmonary embolism (PE), in order to minimize the requirement for pulmonary computed tomography angiography (CTA).
Purpose: To evaluate whether doubling the threshold value of serum D-dimer from 500 μg/L to 1000 μg/L could safely reduce utilization of pulmonary CTA to exclude PE in our emergency department patient population.
Material and methods: Emergency department patients evaluated for PE with a quantitative D-dimer assay and pulmonary CTA were eligible for inclusion. D-dimer values were retrospectively collected in all included patients. Pulmonary CT angiograms were reviewed and scored as positive or negative for PE. Receiver-operating characteristic (ROC) analysis was used to determine the accuracy of quantitative D-dimer measurements in differentiating between positive and negative PE patients as per CTA.
Results: A total of 237 consecutive patients underwent pulmonary CTA and had a D-dimer measurement performed. Median D-dimer level was 1007 μg/L and in 11 (5%) patients the pulmonary CT CTA was positive for PE. The ROC curve showed an area under the curve (AUC) of 0.91 (P < 0.0001). Increasing the D-dimer threshold value of 500 μg/L to 1000 μg/L increased the specificity from 8% to 52% without changing the sensitivity.
Conclusion: Adjusting the D-dimer cut-off value for the emergency department community population and patient age increases the yield and specificity of the ELISA D-dimer assay for the exclusion of PE without reducing sensitivity.