Introduction Although temporal variation is the hallmark of asthma, recommended diagnostic approaches largely rely on single clinic-based measurements. Ambulatory monitoring captures diurnal and day-to-day variability and may therefore enhance diagnostic accuracy. We evaluated the clinical feasibility and potential utility of home spirometry and fractional exhaled nitric oxide (FeNO) monitoring in asthma diagnosis.

Methods Symptomatic, untreated adults with GP-suspected asthma underwent diagnostic tests including bronchodilator reversibility, in-clinic FeNO, blood eosinophil counts and bronchial challenge. Participants measured spirometry and FeNO four times daily over one week; during the second week spirometry were measured twice daily. The reference standard was provided (asthma/not-asthma) by an expert panel of at least two asthma specialists based on clinical history and the results of all in-clinic testing; home spirometry (except for peak expiratory flow) and FeNO measurements were blinded to the panel.

Results Of 67 eligible participants, 51(76%) were recruited, and 38 had asthma confirmed or excluded by the panel. 1058 home spirometry measurements were obtained from 37(73%) participants; 848 home FeNO readings were obtained from 39(76%) participants. Among those completing at least one home measurement, median (IQR) adherence was 66.7(58.6-97.6)% for spirometry and 78.5(51.8-103.6)% for FeNO. Collection of health impact data for economic evaluation was feasible. In participants with a confirmed diagnostic outcome who completed home measurements (FeNO: n=32; spirometry: n=28), the putative home-testing metrics demonstrated high sensitivities at ≥90% specificity, and outperformed peak expiratory flow diurnal variability. Incorporating home testing into the BTS/NICE/SIGN 2024 diagnostic pathway had the potential to reduce reliance on bronchial challenge testing by 57%.

Conclusions Home spirometry and FeNO testing and the prospective collection of health-economic data in the diagnostic setting were feasible. Home-based testing strategy showed early potential to improve asthma diagnosis and pathway efficiency. These findings support further evaluation through an adequately powered diagnostic accuracy study and health-economic assessment.

Key messages

What is already known on this topic: Asthma can be difficult to diagnose, as objective tests may be normal when assessments are performed during periods of minimal or intermittent symptoms.

What this study adds: Our data suggest that home spirometry and FeNO monitoring could be successfully implemented within a diagnostic accuracy trial. Participants were able to perform these tests reliably in the home environment.

How this study might affect research, practice or policy: The early findings suggest that home-based physiological monitoring may offer additive diagnostic value beyond standard clinic-based assessments and could reduce reliance on bronchial challenge testing. These results provide a clear rationale for larger diagnostic accuracy trials and for undertaking early health-economic modelling to assess the potential impact on clinical pathways and resource utilisation.

The authors have declared no competing interest.

ISRCTN 11676160

This study was funded by National Institute for Health Research (NIHR) Research for Patient Benefit Grant (NIHR203591) and supported by the Manchester NIHR Biomedical Research Centre (BRC) (grant no. BRC-1215-20007, and NIHR203308), Asthma UK/Innovate (grant no. AUK-PG-2018-406) and North West Lung Centre Charity. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethics committee of North West - Greater Manchester East Research Ethics Committee gave ethical approval for this work (Reference: 18/NW/0777)

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

RW, MB, AS, SJF, HD and CSM are supported by the NIHR Manchester BRC. RW is supported by NIHR Clinical Lectureship (CL-2023-06-003). HJD is supported by MRC-CSF-MR/V029460/1

Competing Interests statement: We declare no competing interests.

Data sharing statement: The authors will consider all reasonable requests for deidentified data, following approval by the study sponsors. Proposals should be directed to research.sponsormft.nhs.uk. To gain access, data requestors will need to sign a data access agreement.

Funding: This study was funded by National Institute for Health Research (NIHR) Research for Patient Benefit Grant (NIHR203591) and supported by the Manchester NIHR Biomedical Research Centre (BRC) (grant no. BRC-1215-20007, and NIHR203308), Asthma UK/Innovate (grant no. AUK-PG-2018-406) and North West Lung Centre Charity. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care

The authors will consider all reasonable requests for deidentified data, following approval by the study sponsors. Proposals should be directed to research.sponsormft.nhs.uk. To gain access, data requestors will need to sign a data access agreement.