Navigating bronchodilator response in impulse oscillometry: are the latest cut-offs the optimal choice?

<bold>Background:</bold> Proposed new bronchodilator response (BR) cut-offs for impulse oscillometry (IOS) have introduced variations in interpretation. <bold>Aims and Objectives:</bold> This study aims to compare positive BR rates using different cut-offs for IOS indices, including new standards (R5 -40% or X5 +50% in children, R5 -32%, R5 -40%, X5 +44%, or X5 +50% in adults, or AX -80%), as well as earlier cut-offs (R5 -25%, Fres -20%, or AX -40%). <bold>Methods:</bold> A retrospective study analyzed 745 IOS results from children aged 2-12 years and 255 IOS results from individuals aged 12-84 years with recurrent respiratory symptoms at the Community Healthcare Center, Vietnam, from 01/2023 to 01/2024. All IOS results met ERS 2020 quality standards. Patients underwent a BR test with 400 mcg salbutamol MDI through a spacer, with a 15-20 minute waiting time. <bold>Results:</bold> In the children group, positive BR rates with R5 -25% and -40% were 20.9% and 2.0%, respectively; X5 +50% was 1.3%; AX -40% and -80% were 38.0% and 1.9%, respectively; Fres -20% was 18.0%. In the adult group, positive BR rates with R5 -25%, -32%, and -40% were 13.3%, 6.3%, and 0.8%, respectively; X5 +44% and +50% were 2.4% and 2.4%, respectively; AX -40% and -80% were 32.6% and 1.2%, respectively; Fres -20% was 16.1%. The new cut-offs yielded markedly lower positive BR results. X5 -50% in children was 7.3%, and X5 -44% in adults was 10.6%, followed by Fres and AX, indicating substantial internal variation. <bold>Conclusions:</bold> The latest recommended cut-offs might not be universally suitable for all populations, and the R5 index may provide a more valuable BR assessment. References: 1. Thamrin C et al. European Respiratory Journal. 2022;59(3).