Normal d-dimer levels in emergency department patients suspected of acute pulmonary embolism

Objectives We sought to determine: 1) whether normal d-dimer enzyme-linked immunosorbent assay (ELISA) assays predicted the absence of pulmonary embolism (PE) in the high-volume emergency department (ED) of the Brigham and Women’s Hospital, and 2) whether ED physicians accepted normal d-dimer levels as confirmation of no PE without further diagnostic testing such as lung scanning, chest computed tomography (CT) scanning, or pulmonary angiography. Background Although the plasma d-dimer ELISA is a sensitive screening test for excluding acute PE, this laboratory marker has not been widely integrated into clinical algorithms such as creatine kinase-MB fraction or troponin testing for acute myocardial infarction. Methods We mandated that ED physicians order d-dimer ELISA tests on all patients suspected of acute PE. We reviewed the clinical record of each ED patient initially evaluated for suspected PE during the year 2000. We determined whether additional imaging tests for PE were obtained and whether the final diagnosis was PE. Results Of 1,106 d-dimer assays, 559 were elevated and 547 were normal. Only 2 of 547 had PE despite a normal d-dimer. The sensitivity of the d-dimer ELISA for acute PE was 96.4% (95% confidence interval [CI]: 87.5% to 99.6%), and the negative predictive value was 99.6% (95% CI: 98.7% to >99.9%). Nevertheless, 24% of patients with normal d-dimers had additional imaging tests for PE. Conclusions The d-dimer ELISA has a high negative predictive value for excluding PE. By paying more attention to normal d-dimer results, fewer chest CT scans and lung scans will be required, and improvements may be realized in diagnostic efficiency and cost reduction.