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

Inclusion Criteria:

• Patients referred by GP with either (a) possible incident asthma or (b) a diagnostic label of asthma without prior confirmatory objective diagnosis
• Age≥18 years
• Willing to allow his or her General Practitioner and consultant, if appropriate, to be notified of participation in the study
• Able to give informed consent

Exclusion Criteria:

• Age <18 years
• A chest infection or exacerbation requiring antibiotics or steroids within 4 weeks of testing
• Contraindications to spirometry testing
• Established or coded diagnosis of COPD
• Pregnancy or lactating
• Other medical condition that in the opinion of the investigator would preclude compliance with the study protocoll
• Inability to understand English
• Involvement in Clinical Trial of an Investigational Medicinal Product

Participants will be eligible if being referred by their doctor for investigation for possible asthma, or for confirmation of asthma due to absence of objective diagnosis