Pneumonia - Diagnosis

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Highlights	Risk Factors	Surgery
Introduction	Diagnosis	Prevention
Causes	Treatment	Resources
Symptoms	Medications	References
Prognosis	Antibiotic and Antiviral Drug Classes

Urine Tests. Urine antigen tests for Legionella pneumophila (Legionnaires' disease) and Streptococcus pneumoniae may be performed in patients with severe CAP. The S. pneumoniae test takes only 15 minutes and may identify up to 77% of pneumonia cases and rule out S. pneumoniae infection in 98% of patients. It may not be useful in children.

Invasive Tests. In critically-ill patients with ventilator-associated pneumonia, doctors have tried sampling fluid taken from the lungs or trachea. These techniques enabled the physicians to identify the pneumonia-causing bacteria and start the appropriate antibiotics. However, this made no difference in the length of stay in the ICU or hospital, and there was no significant difference in outcome.

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Chest X-Rays and Other Imaging Techniques

X-Rays. A chest x-ray is nearly always taken on a patient admitted to the hospital to confirm a pneumonia diagnosis. This does not need to be repeated if the patient gets better.

X-rays are a form of electromagnetic radiation (like light). They are of higher energy, however, and can penetrate the body to form an image on film. Structures that are dense (such as bone) will appear white, air will be black, and other structures will be shades of gray depending on density. X-rays can provide information about obstructions, tumors, and other diseases, especially when coupled with the use of barium and air contrast within the bowel.

A chest x-ray may reveal the following:

Complications of pneumonia, including pleural effusions and abscesses
White areas in the lung called infiltrates, which indicate infection

Other Imaging Tests. Computed tomography (CT) scans or magnetic resonance imaging (MRI) scans may be useful in some circumstances, especially when:

A lung tumor is suspected
Complications occur
Patients do not respond to antibiotics
Patients have other serious health problems
Pulmonary embolism is suspected
X-ray results are unclear

Click the icon to see an image of a CT scan.

CT and MRI can help detect tissue damage, abscesses, and enlarged lymph nodes. They can also detect some tumors that block bronchial tubes. No imaging technique can determine the actual organism causing the infection. However, features on the CT scan of patients with certain forms of pneumonia -- for example, that caused by Legionella pneumophila -- are usually different from features produced by other bacteria in the lungs.