A 33-year-old man has cough and breathlessness, worsening during the week related to his occupation. What further investigation is most appropriate?

In this scenario, the 33-year-old man's cough and breathlessness that worsen during the week related to his occupation suggest a potential occupational asthma or a respiratory condition linked to exposure to specific allergens or irritants at work. The most appropriate investigation is the measurement of IgE antibodies to isocyanate because it can help confirm sensitization to a specific occupational allergen, particularly in individuals exposed to isocyanate compounds commonly found in various industries, including paint and foam manufacturing.

Measuring IgE antibodies provides direct evidence of the immune response to a suspected allergen and can aid in establishing a diagnosis of allergic bronchospasm or sensitization linked to his work environment. This is particularly useful in the context of occupational asthma, as it identifies whether specific antibodies are present in response to known work-related exposures.

Other investigations, while potentially valuable in different contexts, may not specifically establish the link between the man's symptoms and occupational exposure to isocyanates. For instance, a cardiorespiratory exercise test typically evaluates exercise-induced asthma rather than occupational causes, a histamine challenge assesses non-specific bronchial hyperreactivity but does not target occupational allergens, and serial peak expiratory flow rate measurements, while helpful in monitoring asthma, do not provide specific serological