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Three Part Question

In [ED patients with suspected pneumonia], is [chest x-ray as sensitive as chest CT] for [supporting a diagnosis of pneumonia]?

Clinical Scenario

A 28 year old male presents to the emergency department with a 2-week history of cough and progressive shortness of breath. An outside chest x-ray was non-diagnostic. Chest CT here demonstrates bilateral interstitial infiltrates, consistent with pneumonia. You wonder how often CT scan is necessary to diagnose a pneumonia after an equivocal chest x-ray.

Search Strategy

In [ED patients with suspected pneumonia], is [chest x-ray as sensitive as chest CT] for [supporting a diagnosis of pneumonia]?
Medline 1996-present using the OVID interface.
[(exp pneumonia/ OR pneumonia.mp.) AND (chest xray or CXR).mp. AND (computed tomography or ct).mp.]
LIMIT to English language and humans

Search Outcome

Altogether 30 papers were identified, of which four were relevant to the question. Details are shown in table 1.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Maughan BC et al. Aug 2014 USA	428 ED patients from a single center admitted with a diagnosis of pneumonia	Retrospective cohort study	Percent of diagnoses made by chest x-ray vs chest CT	11% of patients diagnosed by CT after negative / nondiagnostic chest x-ray	Single-center, retrospective design, not all CXR-diagnosed pts received CT
Self WH et al. Feb 2013 USA	3423 ED patients from 12 EDs who received both CXR and chest CT	Retrospective cohort study	Opacity, infiltrate, consolidation, pneumonia, or bronchopneumonia on radiology report	CXR sensitivity 43.5% CXR positive predictive value 26.9%	Retrospective study design, reliance on CT as gold standard
Cereser L et al. Mar 2010 Italy	64 immuno-compromised patients with clinically suspected pneumonia	Experimental study	Retrospective read of CXR as consistent with pneumonia	CXR sensitivity 39-58.5% without clinical information, 41.5-43.9% with.	Small number of patients, reads by two radiologists, limited patient population
Hayden GE and Wrenn KW 2009 USA	97 ED patients from a single center with a diagnosis of pneumonia who received both CXR and chest CT	Retrospective cohort study	Numbers of negative or non-diagnostic chest radiographs in the setting of diagnostic CT scans	27% of patients diagnosed by CT after negative / nondiagnostic chest x-ray	Single-center, retrospective design

Comment(s)

All studies noted a higher sensitivity of CT compared to chest x-ray in the diagnosis of pneumonia. The largest retrospective study also analyzed false positive CXR findings and noted a very low positive predictive value. Of note, in the small single study investigating an immunocompromised patient population, there was no significant difference in the sensitivity of CXR with clinical context versus without. In total, while CXR may provide supporting data in the context of an elevated index of suspicion, its sensitivity and specificity are inadequate to be relied upon to rule in or out a diagnosis of pneumonia.

Clinical Bottom Line

Computed tomography is more sensitive than chest x-ray for the diagnosis of pneumonia; a negative or nondiagnostic CXR in the context of a high clinical suspicion should not be used to rule out this diagnosis.

References

1. Maughan BC; Asselin N; Carey JL; Sucov A; Valente JH. False-negative chest radiographs in emergency department diagnosis of pneumonia. Rhode Island Medicine Aug 2014; 97(8):20-3
2. Self WH; Courtney DM; McNaughton CD; Wunderink RG; Kline JA. High discordance of chest x-ray and computed tomography for detection of pulmonary opacities in ED patients: implications for diagnosing pneumonia. American Journal of Emergency Medicine Feb 2013; 31(2):401-5
3. Cereser L; Zuiani C; Graziani G; Girometti R; Como G; Zaja F; Bazzocchi M. Impact of clinical data on chest radiography sensitivity in detecting pulmonary abnormalities in immunocompromised patients with suspected pneumonia. Radiologia Medica Mar 2010; 115(2):205-14
4. Hayden GE; Wrenn KW. Chest radiograph vs. computed tomography scan in the evaluation for pneumonia. Journal of Emergency Medicine Apr 2009; 36(3):266-70