How to Diagnose Pneumonia

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Pneumonia can be suspected initially on the basis of clinical signs and symptoms like fever, cough with sputum, breathlessness, chest pain. There maybe some atypical signs like absence of fever if the patient is immuno-compromised or malnourished. Cough maybe dry, depending upon the cause of pneumonia. There might be confusion, lethargy, abdominal pain and lethargy if it pneumonia is due to legionella. Past history of exposure and occupational history might give some clue about cause of pneumonia.

Chest X-ray

As far as tests are concerned chest x-ray is the single most initial test which not only tells about the presence of disease but also initial clue to determining the diagnosis. On the basis of chest X-ray it can be determine if the disease is restricted to one lobe (Lobar Pneumonia) or it is bilaterally present in both the lungs with interstitial infiltrates. X-ray also helps in finding out if pneumonia is associated with pleural effusion or not.

Lobar Pneumonia is mainly caused by typical agents like s.pneumoniae, haemophilus, morexella.

Interstitial Infiltrates : Seen mainly in pneumonia caused by pneumocyctis, mycoplasma, chlamydia, coxiella and sometimes legionella.

Sputum culture

Sputum also helps in diagnosing pneumonia, it might be rusty colored if caused by s.pneumoniae or currant jelly if the causative organism is klebsiella. The sputum culture is the most specific test for diagnosing lobar pneumonia as the other atypical organisms do not produce enough sputum and also difficult to show up on Grams stain or regular bacterial culture.

Other tests

Sometimes invasive tests are required to diagnose pneumonia like bronchoscopy, thoracentesis, pleural biopsy, or culture of pleural fluid.

Most specific test for diagnosing pneumonia is with open lung biopsy which is almost never performed.

Specific diagnostic methods for diagnosing pneumonia based on causative organism

Mycoplasma : antibody titre. Cold agglutinins can also be performed but it has limited sensitivity and specificity.

Peumocyctis Jiroveci: Bronchioalveolar lavage. Increased LDH.

Coxiella, Chlamydia (Pneumoniae and Psittaci), coccidioidomycoses : specific antibody titres.

Legionella: Bacteria can be cultured in charcoal yeast extract, urine antigen test, direct fluorescent antibodies and specific antibody titers.