The WISDOM study (NCT00975195) reported a change in lung function following withdrawal of fluticasone propionate in patients with severe to very severe COPD treated with tiotropium and salmeterol. However, little is known about the validity of home-based spirometry measurements of lung function in COPD. Therefore, as part of this study, following suitable training, patients recorded daily home-based spirometry measurements in addition to undergoing periodic in-clinic spirometric testing throughout the study duration. We subsequently determined the validity of home-based spirometry for detecting changes in lung function by comparing in-clinic and home-based forced expiratory volume in 1 second in patients who underwent stepwise fluticasone propionate withdrawal over 12 weeks versus patients remaining on fluticasone propionate for 52 weeks. Bland-Altman analysis of these data confirmed good agreement between in-clinic and home-based measurements, both across all visits and at the individual visits at study weeks 6, 12, 18, and 52. There was a measurable difference between the forced expiratory volume in 1 second values recorded at home and in the clinic (mean difference of -0.05 L), which may be due to suboptimal patient effort in performing unsupervised recordings. However, this difference remained consistent over time. Overall, these data demonstrate that home-based and in-clinic spirometric measurements were equally valid and reliable for assessing lung function in patients with COPD, and suggest that home-based spirometry may be a useful tool to facilitate analysis of changes in lung function on a day-to-day basis.
Keywords: FEV1; home-based spirometry; inhaled corticosteroid; lung function; severe COPD.