Diagnostic Accuracy of a Bedside D-dimer Assay and Alveolar Dead-Space Measurement for Rapid Exclusion of Pulmonary Embolism

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Abstract
Research from JAMA — Diagnostic Accuracy of a Bedside D-dimer Assay and Alveolar Dead-Space Measurement for Rapid Exclusion of Pulmonary Embolism — A Multicenter Study — ContextA previous study suggested that the combination of a normal D-dimer assay and normal alveolar dead-space fraction is a highly sensitive screening test for pulmonary embolism (PE).ObjectiveTo determine if the combination of a normal alveolar dead-space fraction (volume of alveolar dead space/tidal volume ≤20%) and a normal whole-blood agglutination D-dimer assay can exclude PE in emergency department (ED) patients.DesignProspective, noninterventional study conducted in 1998-1999. Study data were obtained prior to standard testing for PE, consisting of radionuclide lung scanning or contrast-enhanced computed tomography and 6-month follow-up plus selective use of venous ultrasonography and pulmonary angiography. Imaging studies were interpreted by blinded observers.SettingSix urban teaching hospitals in the United States.PatientsA total of 380 hemodynamically stable ED patients aged 18 years or older with suspected acute PE.Main Outcome MeasuresSensitivity and specificity for PE with a positive test defined as having either alveolar dead-space fraction or D-dimer assay results abnormal. Alveolar dead-space fraction was determined by subtracting airway dead space from physiological dead space (determined using the modified Bohr equation) and D-dimer assay, assayed at bedside using 20 µL of arterial blood.ResultsPulmonary embolism was diagnosed in 64 patients (16.8%), of those 20 had an abnormal D-dimer assay result, 3 had an abnormal alveolar dead-space fraction, 40 had abnormal results in both, and 1 had normal results for both tests. The sensitivity for diagnosis of PE was 98.4% (95% confidence interval [CI], 91.6%-100.0%). Among the 316 patients without PE, both D-dimer and dead-space results were normal in 163, for a specificity of 51.6% (95% CI, 46.1%-57.1%). Posterior probability of PE with normal results on both tests was 0.75% (95% CI, 0%-3.4%).ConclusionIn this multicenter study of ED patients, a normal D-dimer assay result plus a normal alveolar dead-space fraction was associated with a low prevalence of PE.