A diagnosis of pneumonia is typically achieved by which of the following diagnostic tests?
A. ABG analysis
B. Chest x-ray
C. Blood cultures
D. Sputum culture and sensitivity
Correct Answer: D. Sputum culture and sensitivity
Sputum C & S is the best way to identify the organism causing the pneumonia. If good quality, sputum evaluation may reveal more than 25 WBC per low-power field and less than 10 squamous epithelial cells. Some bacterial causes present with specific biochemical evidence, such as Legionella, may present with hyponatremia and microhematuria.
Option A: ABG analysis will determine the extent of hypoxia present due to the pneumonia. An arterial blood gas may reveal hypoxia and respiratory acidosis. Pulse oximetry of less than 92% indicates severe hypoxia, and elevated CRP predicts a serious infection.
Option B: Chest x-ray will show the area of lung consolidation. Findings may vary from lobar to interstitial infiltrate, to occasionally cavitary lesions with air-fluid levels suggestive of a more severe disease process.
Option C: Blood cultures will help determine if the infection is systemic. These include a series of tests like blood culture, sputum culture and microscopy, routine blood counts, and lymphocyte count. Special tests such as urinary antigen testing, bronchial aspirate, or induced sputum may be used for certain pathogens.
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