Horsley AR, Belcher J, Bayfield K, et al. - Researchers sought to evaluate feasibility, repeatability and longitudinal lung clearance index (LCI) change in children and adults with cystic fibrosis (CF) with predominantly mild baseline disease in order to help inform clinical practice. Repeated LCI measurement at the time of clinical review in patients with CF > 5 years, administered utilising a quick wash-in system, in a prospective, 3-year, multicentre, observational study. At the end of the study, 112 patients had completed at least one LCI assessment, and 98 (90%) were still being followed up on. The majority of CF patients with preserved lung function have stable LCI over time. It is possible to identify cluster behaviours, and baseline LCI is a risk factor for future progression. Such findings support the use of LCI in clinical practice to identify patients at risk of declining lung function.