Diagnosis of pneumonia
Complete blood count: WBC count is often increased with a polymorphic predominance in bacterial infections. Lymphocytic predominance may be seen in viral pneumonias, pertussis and atypical infections.
Cultures: In the cooperative older child with a productive cough, a sputum Gram stain is useful. Sputum cultures and immunofluorescent antibody testing may be useful. Bactec cultures (sputum or blood) are useful to isolate the organisms).
Imaging Studies: Chest x-ray PA view is the diagnostic test for pneumonias. Sometimes to differentiate from a sine-pneumonic effusion, a USG chest may be required. In rare cases of children who have an effusion or an empyema identified on CXR, a CT scan may be needed to further define the scope of the problem.
Mantoux Test: To diagnose pneumonia due to mycobacterial tuberculosis.
Cold agglutinin test: A bedside cold agglutinins test may help confirm the clinical suspicion of mycoplasmal infection. This test is performed by placing a small amount of blood in a specimen tube containing anticoagulant and inserting this into a cup filled with ice water. After a few minutes in the cold water the tube is held up to the light, tilted slightly, and slowly rotated. Small clumps of red blood cells coating the tube are indicative of a positive test result. This test is positive only in about one half of the cases of mycoplasmal infection and has high chances of false positive reactions.
Other tests: If there is presence of pleural fluid, pleural fluid aspiration and culture and microscopy.
Differentiation between bacterial and viral pneumoniaBacterial pneumonia: Usually associated with a fever more than 103 degree F. It is often a lobar, segmental or rounded well-defined pneumonia affecting a single lobe or multiple lobes. There may associated pleural effusion with abscess, bullae or pneumatoceles.
Viral pneumonia: The fever is usually lower than 103 degree F. The pneumonia is poorly defined, interstitial or peribronchial affecting multiple sites predominantly in multiple sites and poorly defined. There may be subsegmental atelectasis.