12th January 2024

Investigations

Investigations in suspected pneumonia aim to confirm the diagnosis, establish the causative pathogen and determine the severity.

Investigations to consider include:

• Blood tests
  • Full blood count – to assess the white cell count and differential. Mycoplasma infection can also cause cold autoimmune haemolytic anaemia. If this is suspected, the full blood count should be followed up with a blood film showing spherocytes and reticulocytosis and direct antiglobulin test (DAT).
  • Urea & electrolytes – urea is included as part of the CURB-65 score. Legionella pneumonia is typically associated with hyponatraemia.
  • Liver function tests – Legionella can cause deranged liver function tests
  • C-reactive protein
  • Blood cultures
  • Venous blood gas for lactate
  • Serology for atypical organisms, e.g. Mycoplasma
• Arterial blood gas – if hypoxic
• Chest X-ray to assess for consolidation
• Sputum culture
• Urine for Legionella and Pneumococcal antigens

Image Source: Wikimedia Commons (2017).  X-ray_of_lobar_pneumonia, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/5/51/X-ray_of_lobar_pneumonia.jpg (Accessed: 22 February 2022).