Utility and interpretation of multiple breath washout in children with cystic fibrosis.

Transformative changes in the health of children with cystic fibrosis (CF) mean that more sensitive outcome measures are needed to monitor paediatric CF lung disease. Multiple breath washout (MBW) and its primary readout lung clearance index are gaining increasing traction as an endpoint for clinical trials in the CF space and show promise as a clinical investigation. In this article, we use four clinically based questions to explore what MBW can and cannot (yet) do and highlight some of its strengths and weaknesses as an investigation. We end by discussing how we can increase the utility of MBW as an investigation in children with CF.