Airway surface liquid pH in paediatric patients with cystic fibrosis

Background: Cystic fibrosis (CF) patients have more acidic airway surface liquid (ASL), which can denature antimicrobial defensins. Induced sputum is non-invasive and is as representative as bronchoalveolar lavage. Objectives: The objectives of this study were to analyse the ASL pH obtained by induced sputum and assess the relationship between clinical features in paediatric CF patients. Methods: This is a prospective observational study in CF paediatric patients. Sputum was induced in a patient by inhaling 4.5% hypertonic saline, the sputum was collected into a sterile container for pathological analysis, and the pH was measured from the liquid part (ASL) in a gas machine. Results: A total of 27 patients were included in the study: mean age (11.96 ± 3.9) years, mean sweat test (99.38 ± 17.76) ng/L, common mutation Del508F (N24, 88.8%), mean FEV1% 91.94% ± –12.6%, Staphylococcus colonization 14 (51.9%), normal chest CT 8 (29.6%), air trapping 12 (44.4%), bronchiectasis 6 (22.2%), and mean ASL pH 6.72 ± 0.06 (n = 15). A significant correlation was found between a higher sweat test and lower ASL pH (R = 0.683, p = 0.005). There were no differences between altered chest CT (p = 0.199) and positive Staphylococcus aureus (p = 0.17). Conclusion: This is the first publication that use induced sputum to obtain the ASL pH in CF patients. The ASL pH in CF patients is usually acidic and correlated with altered transmembrane function conductance.