17th February 2025

Investigating pneumonia

Patients with bacterial pneumonia often present with a productive cough, shortness of breath and fever. They may be tachypnoeic with localised crackles with dullness to percussion on auscultation, reflecting underlying consolidation. Other symptoms or signs typical of any severe infection, such as tachycardia and reduced urine output, may also be present.

Initial investigations

A full history, examination, bloods and a chest X-ray would be expected as a minimum. Blood cultures and sputum cultures may be useful, especially for atypical organisms. Urine samples may be used to look for pneumococcal or Legionella antigen; PCR is necessary for confirmation of Mycoplasma.

If unable to achieve samples, a bronchoalveolar lavage may help. If there is an effusion, a pleural aspirate may offer a diagnosis. A pH <7.2 is diagnostic of a complicated parapneumonic effusion. If the patient requires a pleural tap, the triangle of safety offers borders which minimise the risk of iatrogenic harm: lateral border of the pectoralis major, lateral border of the latissimus dorsi and line of the fifth intercostal space.

Further investigations

A CT thorax can be used in severe cases or to assess for cavitation or abscess. A pulmonary abscess could be from septic emboli from endocarditis and an echocardiogram would be recommended. 

Recurrent or atypical bacterial pneumonia should prompt consideration of an underlying immunodeficiency such as HIV or cancer, including myeloma. Alternatively, recurrent bacterial infections in a young person with worsening respiratory function may prompt testing for cystic fibrosis or alpha-1 antitrypsin deficiency-related COPD.

On discharge, patients should be followed up with a 6 week post-discharge chest X-ray to assess for resolution and possible underlying causes of pneumonia, including malignancy.