RT Journal Article SR Electronic T1 Lung function in children with cystic fibrosis in the USA and UK: a comparative longitudinal analysis of national registry data JF Thorax JO Thorax FD BMJ Publishing Group Ltd and British Thoracic Society SP thoraxjnl-2021-216849 DO 10.1136/thoraxjnl-2021-216849 A1 Daniela K Schlüter A1 Josh S Ostrenga A1 Siobhán B Carr A1 Aliza K Fink A1 Albert Faro A1 Rhonda D Szczesniak A1 Ruth H Keogh A1 Susan C Charman A1 Bruce C Marshall A1 Christopher H Goss A1 David Taylor-Robinson YR 2021 UL http://thorax.bmj.com/content/early/2021/07/01/thoraxjnl-2021-216849.abstract AB Rationale A previous analysis found significantly higher lung function in the US paediatric cystic fibrosis (CF) population compared with the UK with this difference apparently decreasing in adolescence and adulthood. However, the cross-sectional nature of the study makes it hard to interpret these results.Objectives To compare longitudinal trajectories of lung function in children with CF between the USA and UK and to explore reasons for any differences.Methods We used mixed effects regression analysis to model lung function trajectories in the study populations. Using descriptive statistics, we compared early growth and nutrition (height, weight, body mass index), infections (Pseudomonas aeruginosa, Staphylococcus aureus) and treatments (rhDnase, hypertonic saline, inhaled antibiotics).Results We included 9463 children from the USA and 3055 children from the UK with homozygous F508del genotype. Lung function was higher in the USA than in the UK when first measured at age six and remained higher throughout childhood. We did not find important differences in early growth and nutrition, or P.aeruginosa infection. Prescription of rhDNase and hypertonic saline was more common in the USA. Inhaled antibiotics were prescribed at similar levels in both countries, but Tobramycin was prescribed more in the USA and colistin in the UK. S. aureus infection was more common in the USA than the UK.Conclusions Children with CF and homozygous F508del genotype in the USA had better lung function than UK children. These differences do not appear to be explained by early growth or nutrition, but differences in the use of early treatments need further investigation.Data may be obtained from a third party and are not publicly available. The data used in this study are from the US CF Foundation Patient Registry and the UK CF Registry. The data are available from the respective organisations on reasonable request.