Reference percentiles for FEV₁ and BMI in European children and adults with cystic fibrosis

Background: The clinical course of Cystic Fibrosis (CF) is usually measured using the percent predicted FEV₁ and BMI Z-score referenced against a healthy population, since achieving normality is the ultimate goal of CF care. Referencing against age and sex matched CF peers may provide valuable information for patients and for comparison between CF centers or populations. Here, we used a large database of European CF patients to compute CF specific reference equations for FEV₁ and BMI, derived CF-specific percentile charts and compared these European data to their nearest international equivalents. Methods. 34859 FEV₁ and 40947 BMI observations were used to compute European CF specific percentiles. Quantile regression was applied to raw measurements as a function of sex, age and height. Results were compared with the North American equivalent for FEV₁ and with the WHO 2007 normative values for BMI. Results: FEV₁ and BMI percentiles illustrated the large variability between CF patients receiving the best current care. The European CF specific percentiles for FEV₁ were significantly different from those in the USA from an earlier era, with higher lung function in Europe. The CF specific percentiles for BMI declined relative to the WHO standard in older children. Lung function and BMI were similar in the two largest contributing European Countries (France and Germany). Conclusion: The CF specific percentile approach applied to FEV₁ and BMI allows referencing patients with respect to their peers. These data allow peer to peer and population comparisons in CF patients.