London Asthma Diagnostics Study

The goal of this trial is to learn if the addition of oscillometry with reversibility testing increases diagnostic accuracy in adult asthma diagnosis, when added to current standard of care tests: spirometry with reversibility testing and Fractional Exhaled Nitric Oxide (FeNO). The main question it aims to answer is: \- Does oscillometry with reversibility testing increase diagnostic accuracy in detection of asthma in adults when added to spirometry with reversibility and FeNO? Researchers will evaluate the diagnostic accuracy of this approach with the reference standard, which is a clinically adjudicated diagnosis of asthma by two respiratory clinicians based on history and investigation results. Participants will * Undergo oscillometry testing alongside their routine asthma investigations within their scheduled clinic visit * Optionally participate in our sub-studies on new breath and nasal swab tests for asthma * Optionally participate in our qualitative substudy on patients views and attitudes to asthma testing and oscillometry