Purpose: The purpose of this study was to assess the ability of d-dimer testing to obviate the need for cross-sectional imaging for patients at "non-high risk" for pulmonary embolism (PE).
Methods: This is a retrospective study of emergency department patients at an academic medical center who underwent cross-sectional imaging (MRA or CTA) to evaluate for PE from 2008 to 2013. The primary outcome was the NPV of d-dimer testing when used in conjunction with clinical decision instruments (CDIs = Wells', Revised Geneva, and Simplified Revised Geneva Scores). The reference standard for PE status included image test results and a 6-month chart review follow-up for venous thromboembolism as a proxy for false negative imaging. Secondary analyses included ROC curves for each CDI and calculation of PE prevalence in each risk stratum.
Results: Of 459 patients, 41 (8.9%) had PE. None of the 76 patients (16.6%) with negative d-dimer results had PE. Thus, d-dimer testing had 100% sensitivity and NPV, and there were no differences in CDI performance. Similarly, when evaluated independently of d-dimer results, no CDI outperformed the others (areas under the ROC curves ranged 0.53-0.55). There was a significantly higher PE prevalence in the high versus "non-high risk" groups when stratified by the Wells' Score (p = 0.03).
Conclusions: Negative d-dimer testing excluded PE in our retrospective cohort. Each CDI had similar NPVs, whether analyzed in conjunction with or independently of d-dimer results. Our results confirm that PE can be safely excluded in patients with "non-high risk" CDI scores and a negative d-dimer.
Keywords: CT; Clinical decision instruments; D-dimer; MRI; Pulmonary embolism.