20th February 2025

Diagnosis of HP

History is essential. Investigations include:

• Bloods: inflammatory markers may be raised (lymphocytosis; non specific). Certain IgG antibodies may support the diagnosis but are not specific. Eosinophilia is not usually present as HP is not a type I hypersensitivity reaction
• CXR: Acute – can be normal or may show diffuse micronodular interstitial shadowing, sometimes with ground-glass change. Chronic – reticular pattern of fibrosis with honeycombing, which can be more severe in the upper lobes. Volume loss and peribronchial thickening may also be visible.
• High-resolution CT: Acute – bilateral, patchy ground-glass opacity and numerous round centrilobular opacities may be seen. Areas of radiolucency may occur due to air trapping. Chronic – diffuse centrilobular nodules, ground-glass change and air trapping. Honeycombing and traction bronchiectasis (predominantly upper lobes)
• Lung function tests: typically restrictive with reduced gas transfer and lung volumes, but obstruction may also be noted, particularly in chronic forms
• Bronchoalveolar lavage: lymphocytosis and a CD4:CD8 ratio <1