Investigations

Chest radiology may reveal diffuse interstitial bilateral perihilar shadowing, though there is a spectrum of appearance ranging from subtle shadowing to extensive consolidation. 10% of radiographs will be normal, whilst 10% will show unusual, perhaps misleading features.

Definitive diagnosis is by bronchial alveolar lavage with silver staining. The lavage is performed using fibreoptic bronchoscopy.

Other tests include:

• Induced sputum techniques may be used, in which the inhalation of nebulised hypertonic saline provokes bronchorrhoea and the coughing up of material from which P. carinii can be identified. This, however takes time and requires meticulous technique.
• serology to identify anti-Pneumocystis antibodies is unreliable
• lactate dehydrogenase is usually raised
• blood gases or some indication of gas transfer function may be performed to determine if the patient is sufficiently ill to require hospitalisation.