False-negative chest radiographs in emergency department diagnosis of pneumonia.

Background: Emergency department (ED) patients frequently undergo chest x-ray (CXR) to evaluate for pneumonia. The rate of false-negative CXR in patients with pneumonia is unclear.
Objectives: Identify patients admitted with pneumonia who were diagnosed by CT despite nondiagnostic CXR.
Methods: Retrospective analysis of quality improvement data on adult ED patients admitted with pneumonia over 21 months. Primary outcome was percent of patients diagnosed by CT despite normal CXR. Patients were classified as CXR-diagnosed if they had CXR and no CT, or if antibiotics were ordered after CXR and before CT. CT-based diagnosis was indicated by administration of antibiotics only after CT was completed.
Results: 49 patients (11.4%) were diagnosed by CT (p<0.001). These patients were younger (p<0.001) and more often complained of chest pain (p<0.001).
Conclusions: Patients with pneumonia may present with normal or nondiagnostic CXR, although false negatives may be less common than previously reported.