Characteristics of pneumonia with negative chest radiography in cases confirmed by computed tomography

Background: Chest radiography is commonly used for diagnosing community-acquired pneumonia (CAP). Computed tomography (CT) is not routinely recommended for initial assessment of CAP patients but is more sensitive and more specific than chest radiography. Objectives: To investigate characteristics of pneumonia with negative chest radiography in cases confirmed by CT. Methods: We included patients diagnosed with CAP in the emergency department, and chest radiography and CT were performed and sputum cultures were collected. The CR- group was defined as patients for whom infiltration of pneumonia was detected only on CT. The CR+ group was defined as patients for whom infiltration was detected on both chest radiography and CT. Data were collected retrospectively from medical records. Results: A total of 138 patients were included, with 58 patients in the CR- group and 80 patients in the CR+ group. Mean age was higher in the CR- group than in the CR+ group, and white blood cell counts and C-reactive protein (CRP) levels were lower in the CR- group than in the CR+ group (8.4 × 10³/μL vs 12.4 × 10³/μL, p = 0.01; 4.7 mg/dL vs 15.6 mg/dL, p < 0.001, respectively). Laterality of the infiltrated lungs differed between groups (right:left:bilateral = 14:30:14 vs 48:20:12, p = 0.006). Multivariate logistic analysis identified leukocytosis, elevated CRP levels (odds ratio (OR) 3.57, p = 0.003), laterality (OR 2.16, p = 0.006) as predictors of pneumonia in the CR- group. Conclusion: In pneumonia with negative chest radiography in cases confirmed by CT, milder inflammation and infiltration in the left lung tended to be seen.