Which reference equation should we use for interpreting spirometry values for First Nations Australians? A cross‐sectional study

Abstract Objectives To evaluate the suitability of the Global Lung Function Initiative (GLI)‐2012 other/mixed and GLI‐2022 global reference equations for evaluating the respiratory capacity of First Nations Australians. Design, setting Cross‐sectional study; analysis of spirometry data collected by three prospective studies in Queensland, the Northern Territory, and Western Australia between March 2015 and December 2022. Participants Opportunistically recruited First Nations participants in the Indigenous Respiratory Reference Values study (Queensland, Northern Territory; age, 3–25 years; 18 March 2015 – 24 November 2017), the Healthy Indigenous Lung Function Testing in Adults study (Queensland, Northern Territory; 18 years or older; 14 August 2019 – 15 December 2022) and the Many Healthy Lungs study (Western Australia; five years or older; 10 October 2018 – 7 November 2021). Main outcome measures Goodness of fit to spirometry data for each GLI reference equation, based on mean Z ‐score and its standard deviation, and proportions of participants with respiratory parameter values within 1.64 Z ‐scores of the mean value. Results Acceptable and repeatable forced expiratory volume in the first second (FEV 1 ) values were available for 2700 First Nations participants in the three trials; 1467 were classified as healthy and included in our analysis (1062 children, 405 adults). Their median age was 12 years (interquartile range, 9–19 years; range, 3–91 years), 768 (52%) were female, and 1013 were tested in rural or remote areas (69%). Acceptable and repeatable forced vital capacity (FVC) values were available for 1294 of the healthy participants (88%). The GLI‐2012 other/mixed and GLI‐2022 global equations provided good fits to the spirometry data; the race‐neutral GLI‐2022 global equation better accounted for the influence of ageing on FEV 1 and FVC, and of height on FVC. Using the GLI‐2012 other/mixed reference equation and after adjusting for age, sex, and height, mean FEV 1 (estimated difference, –0.34; 95% confidence interval CI, –0.46 to –0.22) and FVC Z ‐scores (estimated difference, –0.45; 95% CI, –0.59 to –0.32) were lower for rural or remote than for urban participants, but their mean FEV 1 /FVC Z ‐score was higher (estimated difference, 0.14; 95% CI, 0.03–0.25). Conclusion The normal spirometry values of healthy First Nations Australians may be substantially higher than previously reported. Until more spirometry data are available for people in urban areas, the race‐neutral GLI‐2022 global or the GLI‐2012 other/mixed reference equations can be used when assessing the respiratory function of First Nations Australians.