Brief Report
High discordance of chest x-ray and computed tomography for detection of pulmonary opacities in ED patients: implications for diagnosing pneumonia

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Abstract

Objective

To evaluate the diagnostic performance of chest x-ray (CXR) compared to computed tomography (CT) for detection of pulmonary opacities in adult emergency department (ED) patients.

Methods

We conducted an observational cross-sectional study of adult patients presenting to 12 EDs in the United States from July 1, 2003, through November 30, 2006, who underwent both CXR and chest CT for routine clinical care. CXRs and CT scans performed on the same patient were matched. CXRs and CT scans were interpreted by attending radiologists and classified as containing pulmonary opacities if the final radiologist report noted opacity, infiltrate, consolidation, pneumonia, or bronchopneumonia. Using CT as a criterion standard, the diagnostic test characteristics of CXR to detect pulmonary opacities were calculated.

Results

The study cohort included 3423 patients. Shortness of breath, chest pain and cough were the most common complaints, with 96.1% of subjects reporting at least one of these symptoms. Pulmonary opacities were visualized on 309 (9.0%) CXRs and 191 (5.6 %) CT scans. CXR test characteristics for detection of pulmonary opacities included: sensitivity 43.5% (95% CI, 36.4%-50.8%); specificity 93.0% (95% CI, 92.1%-93.9%); positive predictive value 26.9% (95% CI, 22.1%-32.2%); and negative predictive value 96.5% (95% CI, 95.8%-97.1%).

Conclusion

In this multicenter cohort of adult ED patients with acute cardiopulmonary symptoms, CXR demonstrated poor sensitivity and positive predictive value for detecting pulmonary opacities. Reliance on CXR to identify pneumonia may lead to significant rates of misdiagnosis.

Introduction

A chest x-ray (CXR) is completed during approximately 18.5% of all emergency department (ED) visits in the United States, with an estimated 20.4 million ED CXRs performed annually [1].When evaluating patients with chest symptoms, such as shortness of breath, chest pain and cough, emergency clinicians must decide if CXR findings are consistent with pneumonia. Failure to promptly recognize and treat bacterial pneumonia may lead to significant morbidity and mortality [2], [3]. Meanwhile, inappropriate use of antibiotics for respiratory symptoms not caused by bacterial infection is likely a major contributor to the development of antibiotic resistance [4], [5], [6]. Furthermore, attributing a patient's symptoms to pneumonia based on CXR results when, in fact, pneumonia is not present may lead to diagnostic anchoring and failure to recognize the patient's true illness [7].

Pulmonary opacities, areas of increased attenuation visualized within the lung fields on chest imaging [8], [9], are commonly used as criteria to support a diagnosis of pneumonia [3], [10]. Despite CXR being used as the primary radiographic test to evaluate for pneumonia, the test characteristics of CXR for detecting pneumonia are not well understood. Computed tomography (CT) is a more precise technique for imaging the chest, but has not supplanted CXR as the primary imaging test for pneumonia due to increased time, cost, and radiation exposure associated with CT [11], [12], [13]. However, comparing CXR to CT offers an opportunity to evaluate the accuracy of CXR for demonstrating radiographic findings consistent with pneumonia and to help inform clinicians how to use CXR results when considering a diagnosis of pneumonia. The purpose of this study was to evaluate the diagnostic test characteristics of CXR for detection of pulmonary opacities compared to a chest CT criterion standard in adult ED patients.

Section snippets

Methods

We conducted an observational, multicenter, cross-sectional study of adult ED patients who underwent both a CXR and chest CT as part of their evaluation. The diagnostic test characteristics of CXR for detection of pulmonary opacities were calculated using a concurrent chest CT as a criterion standard. The institutional review board at all participating sites approved this study.

Results

During the study period, 4237 subjects underwent a chest CT scan; 3423 (80.8%) of these subjects also had a CXR completed and were included in the final analyses (Fig.). Demographic and clinical characteristics of these subjects are summarized in Table 1. Shortness of breath, chest pain and cough were the most common presenting complaints, with 96.1% of subjects reporting at least one of these symptoms.

Pulmonary opacities were visualized on 309 (9.0%) CXRs and 191 (5.6 %) CT scans. The

Discussion

From the standpoint of maximizing diagnostic accuracy, an optimal strategy for diagnosing pneumonia would involve culturing specimens obtained from the lower respiratory tract. However, due to the invasive nature of collecting these specimens and the time lapse needed for cultures to grow, this strategy is not practical. Therefore, the standard for diagnosing pneumonia that has developed over the past several decades involves recognition of a syndrome of clinical, laboratory, and radiographic

Conclusion

In this multicenter cohort of adult ED patients with acute cardiopulmonary symptoms evaluated with both CXR and chest CT, 9.8% of patients had discordant findings on CXR and CT with respect to the presence of pulmonary opacities as interpreted by radiologists. Using chest CT as a criterion standard for pulmonary opacities, CXR demonstrated poor sensitivity and PPV. Reliance on CXR to identify pneumonia may lead to significant rates of misdiagnosis. Further research is indicated to investigate

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Support: (1) Supported by the National Institutes of Health (R41HL074415, R42HL074415, K23HL077404 and R01HL074384). (2) Supported by the Office of Academic Affiliations, Department of Veterans Affairs, VA National Quality Scholars Program with resources and the use of facilities at VA Tennessee Valley Healthcare System, Nashville, TN.

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