Health Care Professionals' Estimation of Home Spirometry Use Among People With Cystic Fibrosis: Cross-Sectional Study.

Background: Home spirometry has been widely adopted in the delivery of cystic fibrosis (CF) care. While existing literature largely supports its feasibility and positive outcomes, behavior around home disease monitoring remains poorly understood. Inaccurate assumptions about home spirometry behavior may affect resource prioritization and influence clinical decisions and follow-up. Objective: This study aimed to evaluate health care professionals' (HCPs') ability to estimate home spirometry use among people with CF and compare these estimates with actual recorded data. Methods: Home spirometry data from 48 people with CF attending a large adult CF center in the United Kingdom were obtained from the NuvoAir platform for the period from January to December 2024. The home spirometry data were sampled to represent 3 predefined use categories: infrequent, expected, and highly frequent users. A paper-based survey was distributed to HCPs with experience using home spirometry within the CF service, including physicians, CF specialist nurses, and physiotherapists, with survey dissemination and data collection completed in January 2025. Participants rated their familiarity with each person with CF and estimated their spirometry use both categorically (infrequent, expected, or highly frequent user) and numerically as an open-ended response. CF experience was defined as the number of years worked within the CF service. Estimation accuracy was evaluated using mean bias and mean absolute error (MAE). Results: Of the 29 HCPs invited to participate, 28 (96.6%) responded to the survey, including 10 (35.7%) physicians, 6 (21.4%) nurses, and 12 (42.9%) physiotherapists. There were 790 completed categorical estimates and 794 numerical estimates. The mean CF experience was 15.7 (SD 8.2) years. Across all roles, HCPs systematically underestimated home spirometry use (mean bias -4.9, SD 8.9; MAE 6.32, SD 8.1). No substantial differences in estimation accuracy were observed based on professional role, reported familiarity, or CF experience. Estimation accuracy declined with increasing actual spirometry use, with a strong negative Spearman rank correlation (ρ=-0.88; Conclusions: This study suggests that clinical perception by HCPs alone may not accurately reflect real-world engagement with home spirometry in people with CF. As CF care increasingly incorporates remote monitoring and virtual consultations, understanding actual patient engagement becomes increasingly important. Further qualitative and mixed methods research is needed to better understand the factors influencing home spirometry use and how different patterns of engagement can be effectively identified and supported.