Age and body mass index affect fit of spirometry Global Lung Function Initiative references in schoolchildren

References from the Global Lung Function Initiative (GLI) are widely used to interpret children's spirometry results. We assessed fit for healthy schoolchildren.LuftiBus in the School was a population-based cross-sectional study undertaken in 2013-2016 in the canton of Zurich, Switzerland. Parents and their children aged 6-17 years answered questionnaires about respiratory symptoms and lifestyle. Children underwent spirometry in a mobile lung function lab. We calculated GLI-based z-scores for forced expiratory volume in 1 s (FEVWe analysed data from 2036 children with valid FEVGLI-based FEV