What specific investigations should I consider for a patient suspected of having occupational asthma?

For a patient suspected of having occupational asthma, consider the following specific investigations:

• Serial home peak expiratory flow (PEF) measurements taken at work and away from work to detect variability related to occupational exposure, as this helps to support the diagnosis of occupational asthma.
• Spirometry to assess lung function and look for reversible airflow obstruction characteristic of asthma.
• Bronchodilator reversibility testing with spirometry to identify significant improvement in FEV1 after bronchodilator use, supporting asthma diagnosis.
• Fractional exhaled nitric oxide (FeNO) measurement and blood eosinophil count to detect eosinophilic airway inflammation typical of asthma.
• Skin prick testing or specific IgE testing to identify sensitisation to occupational allergens if relevant.
• Chest radiograph to exclude other pathologies that may mimic or coexist with asthma.

Referral to a respiratory specialist for further assessment, including bronchial challenge testing, may be necessary if diagnosis remains uncertain after initial investigations.

These investigations align with the NICE and BTS/SIGN guidelines on asthma diagnosis and monitoring, which recommend objective tests such as spirometry, FeNO, blood eosinophils, PEF variability, and allergen sensitisation testing to confirm asthma and its triggers, including occupational causes ². Serial PEF monitoring specifically helps to link symptoms to workplace exposure, a key step in diagnosing occupational asthma ². Chest X-ray is advised to exclude alternative diagnoses ¹.