Rationale: Implementation of intervention strategies to prevent lung damage in early cystic fibrosis (CF) requires objective outcome measures that capture and track lung disease.
Objectives: To define the utility of the Lung Clearance Index (LCI), measured by multiple breath washout, as a means to track disease progression in preschool children with CF.
Methods: Children with CF between the ages of 2.5 and 6 years with a confirmed diagnosis of CF and age-matched healthy control subjects were enrolled at three North American CF centers. Multiple breath washout tests were performed at baseline, 1, 3, 6, and 12 months to mimic time points chosen in clinical care and interventional trials; spirometry was also conducted. A generalized linear mixed-effects model was used to distinguish LCI changes associated with normal growth and development (i.e., healthy children) from the progression of CF lung disease.
Measurements and main results: Data were collected on 156 participants with 800 LCI measurements. Although both LCI and spirometry discriminated health from disease, only the LCI identified significant deterioration of lung function in CF over time. The LCI worsened during cough episodes and pulmonary exacerbations, whereas similar symptoms in healthy children were not associated with increased LCI values.
Conclusions: LCI is a useful marker to track early disease progression and may serve as a tool to guide therapies in young patients with CF.
Keywords: cystic fibrosis; disease progression; lung clearance index; lung function.