Objective To evaluate the effect of allergic bronchopulmonary aspergillosis (ABPA) on FEV₁ percent predicted in children and adolescents with cystic fibrosis.

Design Longitudinal data analysis (2008–2010).

Setting Patients participating in the European Cystic Fibrosis Society Patient Registry.

Participants 3350 patients aged 6–17 years.

Main outcome measure FEV₁ percent predicted was the main outcome measure (one measurement per year per child). To describe the effect of ABPA (main explanatory variable) on FEV₁ while controlling for other prognostic factors, a linear mixed effects regression model was applied.

Results In 2008, the mean (±SD) FEV₁ percent predicted was 78.6 (±20.6) in patients with ABPA (n=346) and 88 (±19.8) in those without ABPA (n=2806). After considering other variables, FEV₁ in subjects with ABPA on entry to the study was 1.47 percentage points lower than FEV₁ in patients of similar age without ABPA (p=0.003). There was no FEV₁ decline associated with ABPA over the subsequent study years as the interaction of ABPA with age was not significant (p>0.05). For patients aged 11.82 years (population mean age), poor body mass index had the greatest impact on FEV₁ in 2008, followed by high-risk genotype (two severe mutations), female gender, diabetes mellitus, chronic Pseudomonas aeruginosa infection and ABPA in descending order of effect size.

Conclusions In contrast to the common clinical belief of ABPA having a serious impact on lung function, the difference in FEV₁ between young patients with and without the complication was found to be modest when the effect of other prognostic factors was considered.