Introduction: The clinical impact of routine spirometry with bronchodilator response (BDR) testing in pediatric asthma patients treated with inhaled corticosteroid (ICS) or ICS/long acting beta-agonist therapy (ICS/LABA), is not well known. The purpose of this study was to determine the characteristic spirometry patterns in pediatric patients with treated asthma, and the added clinical value of BDR testing.
 
Methods: Retrospective review of spirometry tests performed for a clinical diagnosis of asthma in patients treated with ICS or ICS/LABA at the Hospital for Sick Children, Toronto, from January 1, 2020 to December 25, 2023.
 
Results: 1015 spirometries with BDR testing in children with a median age of 12.2 (IQR 9.3-15.2) years were included. 546 were normal (54%), 274 (27%) showed an obstructive ventilatory defect with insignificant BDR, and 124 (12%) obstruction with significant BDR, according to ATS criteria. 771 (64%) patients were on ICS/LABA at the time of testing. The frequency of obstruction with insignificant BDR was similar between patients on ICS/LABA or on ICS (27% vs. 25%). In patients on ICS/LABA with insignificant BDR, 42% who underwent scoring by asthma control questionnaire (ACQ) had uncontrolled asthma, and 42% who performed exhaled nitric oxide (eNO) testing had an eNO ?25ppb.

Conclusions: The two most common patterns on spirometry in treated pediatric asthma patients were normal and obstructive ventilatory defect with insignificant BDR. However, in patients treated with ICS/LABA insignificant BDR did not correlate well with ACQ scores or eNO. The clinical utility of routine BDR testing in children with treated asthma may be low and may require a greater level of caution when used to guide therapy.