Can home spirometry and FeNO testing improve asthma diagnosis? a feasibility study

Introduction: Asthma misdiagnosis is common. Despite temporal variability being a hallmark of asthma, diagnosis largely relies on single clinic-based measurements. We evaluated the feasibility and potential diagnostic utility of home spirometry and fractional exhaled nitric oxide (FeNO) testing. Methods: Symptomatic, untreated adults with GP-suspected asthma underwent routine diagnostic tests including bronchodilator reversibility, in-clinic FeNO, blood eosinophil counts and bronchial challenge testing (BCT). Participants also performed home spirometry and FeNO measurements over two weeks. The reference standard (asthma/not-asthma) was determined by an expert panel of at least two asthma specialists based on clinical history and routine test results; home spirometry and home FeNO measurements (index tests) were blinded to the panel. Results: Of 51 recruited participants, 38 had asthma confirmed or excluded by the panel. Home measurements yielded 1058 spirometry recordings from 37 (73%) participants and 848 FeNO recordings from 39 (76%). Among those completing any home measurement, median (IQR) adherence was 66.7(58.6-97.6)% for home spirometry and 78.5(51.8-103.6)% for home FeNO. In participants with a diagnostic outcome (home FeNO: n=32; home spirometry: n=28), the putative home-testing metrics demonstrated high sensitivities at >=90% specificity, outperformed diurnal peak expiratory flow. Incorporating home testing into the BTS/NICE/SIGN 2024 diagnostic pathway could reduce reliance on BCT by 65%. Collection of health impact data was feasible, with economic scoping indicating the potential value for money. Conclusions: Home spirometry and FeNO testing for diagnosing asthma were feasible and showed potential to improve asthma diagnosis. These findings support further evaluation through a fully powered diagnostic accuracy study.