Interobserver Reliability of the Chest Radiograph in Community-Acquired Pneumonia

¹ From the Division of General Internal Medicine, Department of Medicine, University of Pittsburgh
² From the Division of General Internal Medicine, Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh
³ From the Division of General Internal Medicine, Department of Radiology, University of Pittsburgh

Objective: To evaluate the interobserver reliability of pulmonary radiographic findings in patients with community-acquired pneumonia (CAP).

Design: A prospective, muiticenter study.

Setting: Physician offices, medical walk-in clinics, emergency departments, and inpatient wards affiliated with three university hospitals, one community hospital, and one staff model health maintenance organization in three geographic areas.

Methods: Copies of the initial chest radiograph of patients suspected of having CAP were independently read by two staff radiologists at the coordinating university hospital. Interobserver reliability for the interpretation for radiographic findings was assessed by calculation of agreement rates and the kappa statistic.

Participants: Adults (age 18 years) with symptoms or signs of CAP and a pulmonary radiographic infiltrate documented by a local study site radiologist.

Results: Among the 282 patients whose initial pulmonary radiographs were evaluated, there was agreement between the two staff radiologists on the presence of infiltrate in 79.4% and on the absence of an infiltrate in 6.0% (kappa=0.37; 95% confidence interval [CI]=0.22 to 0.52). For the 224 patients with an infiltrate identified by both radiologists, there was further agreement that the infiltrate was unilobar in 41.5% and multilobar in 33.9% (kappa=0.51; 95% CI=0.28 to 0.62), pleural effusion was present in 10.7% and absent in 73.2% (kappa=0.46; 95% CI=0.33 to 0.50), and the infiltrate was alveolar in 96.3% of patients and interstitial in no patients (kappa=0.01; 95% CI=0.03 to 0.00). Among the 210 patients with an alveolar infiltrate, both radiologists classified the infiltrate as lobar in 74.6% and bronchopneumonia in 2.4% (kappa=0.09; 95% CI=0.04 to 0.22), and agreed on the presence of air bronchograms in 7.6% and their absence in 52.9% (kappa=0.01; 95% CI=0.13 to 0.15).

Conclusion: In patients with CAP, two university radiologists identified the presence of infiltrate, multilobar disease, and pleural effusion with fair to good interobserver reliability. However, inter-observer reliability for the pattern of infiltrate and the presence of air bronchograms was poor.

Key Words: agreement • chest radiograph • community-acquired pneumonia • reliability

Submitted on August 29, 1995
Accepted on February 8, 1996

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