Late Breaking Abstract - ERS technical standard: Global Lung Function Initiative reference values for lung clearance index and functional residual capacity

<bold>Background:</bold> Multiple breath washout is a lung function test that assesses lung volume and ventilation distribution. The aim of this analysis was to use the Global Lung Function Initiative methodology to develop all-age reference equations for the multiple breath washout indices lung clearance index (LCI) and functional residual capacity (FRC). <bold>Methods:</bold> Multiple breath washout data from healthy individuals were collated. Data were re-analysed using the latest software versions. Reference equations were derived using the lambda-mu-sigma (LMS) method. The impact of equipment type, inert tracer gas, and equipment dead space volume on the derived reference ranges were investigated. <bold>Results:</bold> Data from 23 sites (n=3647 test occasions) were submitted. Reference equations were derived from 1581 unique observations from participants between the ages of 2 and 81 years. Equipment type, inert tracer gas, and equipment dead space volume did not significantly affect the prediction equations for either LCI or FRC. Reference equations for LCI include age as the only predictor, whereas sex-specific reference equations for FRC included height and age (Figure 1). <bold>Conclusions:</bold> Global Lung Function Initiative all-ages reference equations for LCI and FRC improve our understanding of how these outcomes evolve with age in healthy subjects and provide a new standard for reporting and interpretation. <bold>Funding:</bold> ERS TF-2020-01