Diagnostic Strategies in Pulmonary Embolism

Key to the diagnosis of pulmonary embolism (PE) is a careful bedside evaluation. After this, there are three further diagnostic steps. In all patients, estimation of the clinical probability of PE is performed. The other two steps are measurement of D-dimer when indicated and chest imaging when indicated. The clinical probability of PE is estimated at low, moderate, or high. The prevalence of PE is less than 15% among patients with low clinical probability, 15 to 40% with moderate clinical probability, and >40% in patients with high clinical probability. Clinical gestalt has been found to be very useful in estimating probability of PE. However, clinical prediction rules, such as Wells criteria, the modified Geneva score, and the PE rule out criteria have been advocated as adjuncts. In patients with high clinical probability, the high prevalence of PE can lower the D-dimer negative predictive value, which could increase the risk of diagnostic failure. Consequently, patients with high probability for PE need to proceed directly to chest imaging, without prior measurement of D-dimer level. Key studies in determining which low to moderate probability patients require chest imaging are the Age-adjusted D-dimer cutoff levels to rule out pulmonary embolism (ADJUST-PE), the Simplified diagnostic management of suspected pulmonary embolism (YEARS), and the Pulmonary Embolism Graduated D-Dimer trials. In patients with low clinical probability, PE can be excluded without imaging studies if D-dimer is less than 1,000 ng/mL. In patients in whom there is not a low likelihood for PE, this can be excluded without imaging studies if the D-dimer is below the age-adjusted threshold.