Does a Clinical Decision Rule Using D-Dimer Level Improve the Yield of Pulmonary CT Angiography?

Abstract

This retrospective observational study from the Los Angeles Veterans Administration analyzed the impact of incorporating a clinical decision rule on the yield of pulmonary computed tomography angiography (CTA) in studying pulmonary embolism (PE). From December 2006 to November 2008, the authors implemented guidelines into the CTA order menu in the hospital's electronic medical record system. The ordering physician completed a checklist that generated a Wells score. If the Wells score was 5 or more, a pulmonary CTA using a 64-multi-detector CT scanner was ordered. If the Wells score was 4 or less, the ordering physician was required to obtain an enzyme-linked immunosorbent assay D-dimer level. For D-dimer levels≤500 ng/mL, no CTA was performed. For D-dimer>500, the patient went on to CTA. Patients had 3-month follow-up. During the study period, 261 pulmonary CTA studies were performed on 252 patients (8 patients underwent multiple CT scans), with 43 examinations (16.5%) positive for PE. In the 2 years before the implementation of the clinical decision rule, 196 CTAs were ordered, and 6 (3.1%) were positive for PE. Implementation of the study protocol resulted in a statistically significant increase in the positivity rate of 13.4%, (p<0.0001). In the positive-CTA group, the Wells score was significantly higher than in the negative-CTA group (5.5±2.4 vs 4.5±2.1, p=0.007). The mean D-dimer level was also significantly higher in the positive-CTA group (4956±2892 vs. 2398±2100, p<0.0001). In the study population, the authors found that a combination of a Wells score<4 and a D-dimer<1000 ng/mL had a negative predictive value of 1.0.