An important test for making a diagnosis of pneumonia is a chest x-ray. Chest x-rays can reveal areas of opacity (seen as white) which represent consolidation. Pneumonia is not always seen on x-rays, either because the disease is only in its initial stages, or because it involves a part of the lung not easily seen by x-ray.

Patients with the following conditions should be evaluated with a chest X-ray:^[1]

• Fever (>37.8° C / 100° F)
• Tachypnea (> 20 breaths/min)
• Tachycardia (> 100 bpm)
• Decreased breath sounds and crackles in the physical exam

• X-rays of the chest reveal areas of opacity.
• A normal chest x-ray makes community-acquired pneumonia (CAP) less likely; however, CAP is sometimes not seen on x-rays because the disease is either in its initial stages or involves a part of the lung not easily seen by x-ray.
• X-rays can be misleading, because other problems, like lung scarring and congestive heart failure, can mimic pneumonia on x-ray.^[2] Chest x-rays are also used to evaluate for complications of pneumonia.
• Chest x-ray findings are usually nonspecific in viral pneumonia.
• Computed tomography is used in situations when the diagnosis is not clear with a chest x-ray

• The American Thoracic Society recommends that all patients with a suspicion of nosocomial pneumonia should have a chest x-ray to confirm diagnosis and determine the severity of the disease.^[3]
• A chest X-ray also helps to determine pleural effusions or cavitations, as a possible complication.
• Ideally, the chest X-ray should be posteroanterior and lateral, but this will depend on the patient’s condition.
• Findings include the following:^[4]

• Unilateral or bilateral consolidation
• Air bronchogram
• Pleural effusion
• Cavitation
• Ground glass opacities

• Chest x-ray is also used to assess improvement or lack of clinical response in hospitalized patients.

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