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Patient with chest infection,: A) first choice of radiological investigation.

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The textbooks are unambiguous. Here is the answer:

First-Choice Radiological Investigation for Chest Infection: Chest X-Ray (CXR) — Posteroanterior (PA) View

Why CXR First?

The plain chest radiograph (CXR) is universally the first-line imaging investigation for a suspected chest infection. Multiple authoritative sources confirm this:
  • "The diagnosis of pneumonia requires a chest radiograph; thus, the first decision in the outpatient setting is often whether someone with cough or other respiratory symptoms needs an imaging study to confirm the diagnosis." — Goldman-Cecil Medicine
  • "The plain chest radiograph (CXR) is usually the first imaging test requested by clinicians." — Grainger & Allison's Diagnostic Radiology
  • "All patients with possible community-acquired pneumonia should have a chest radiograph to establish the diagnosis and presence of complications." — Berek & Novak's Gynecology (internal medicine key points)

What CXR Shows in Chest Infection

FindingSuggests
Lobar/segmental consolidationBacterial pneumonia (S. pneumoniae, Klebsiella, Legionella)
Diffuse/patchy bilateral infiltratesViral pneumonia, Pneumocystis jirovecii
CavitationS. aureus, TB (especially upper lobe)
Parapneumonic effusionOccurs in up to 60% of CAP cases
Upper lobe infiltrateTB, histoplasmosis

Why Not CT First?

CT chest has higher sensitivity and specificity than CXR, but is not the initial test because of:
  • Limited availability
  • Higher cost
  • Greater radiation exposure
  • Not necessary in straightforward presentations
CT is reserved for:
  • Complicated pneumonia (e.g., suspected empyema, lung abscess)
  • Abnormal CXR where the cause is uncertain (e.g., ruling out mass, COPD exacerbation, PE)
  • Immunocompromised patients
  • CXR-negative but clinically high suspicion (CT-positive pneumonia)

Summary

Chest X-ray (PA view) → first-line
CT chest → second-line / problem-solving tool
Lung ultrasound → point-of-care adjunct (no standardized criteria; does not replace CXR)
Sources: Goldman-Cecil Medicine (26th ed.); Grainger & Allison's Diagnostic Radiology; Gray's Anatomy for Students; Tintinalli's Emergency Medicine
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