In cystic fibrosis (CF), respiratory disease is the main determinant of prognosis. However, the prevalence and determinants of bronchodilator reversibility (BDR) in pediatric patients remain poorly characterized.

This study aimed to estimate the prevalence of significant BDR and to identify associated clinical and microbiological factors in children with CF (CwCF).

We conducted a retrospective study including CwCF under 20 years of age followed at Armand Trousseau Hospital between April 2018 and July 2024. A total of 48 CwCF and 164 pulmonary function tests (PFTs) including a bronchodilator assessment were analyzed. BDR was assessed using spirometric indexes and respiratory resistance measured by the interrupter technique (Rint). Univariate and multivariate logistic regression analyses were performed to identify factors associated with BDR.

Significant BDR (BDR+) was observed in 16 CwCF (33% [95% CI: 20–48]) at least once during follow-up, mainly detected through a significant decrease in Rint (n = 14, 87.5%), and less frequently through spirometric criteria (increase in forced expiratory volumes, n = 6, 37.5%). In multivariate analysis, BDR+ remained independently associated with the presence of an obstructive ventilatory defect (p = 0.007) and with the total number of PFTs performed (p = 0.035). Chronic colonization with Pseudomonas aeruginosa was associated with BDR+ in univariate analysis (p = 0.006) but not after adjustment (p = 0.30). No significant association was found with sex, clinical asthma, or allergic bronchopulmonary aspergillosis.

Significant bronchodilator reversibility was present in approximately one-third of CwCF, predominantly detected using respiratory resistance measurements. These findings highlight the importance of comprehensive functional respiratory follow-up in CwCF, including resistance measurements, and support a more individualized and functionally guided use of inhaled therapies.