Development and evaluation of spirometry reference equations at high altitude

Approximately 400 million people live at high altitudes worldwide, yet reference equations for spirometry in these populations are inadequately documented. This study aims to develop reference equations for spirometry and assess their applicability to residents at altitudes ranging from 2,100 to 4,700 metres above sea level. This extensive cross-sectional study encompassed healthy non-smokers aged 15 years or older living at Xinjiang and Tibet autonomous region, which covered eight high-altitude areas by a multistage stratified sampling procedure. All individuals underwent pre- and post-bronchodilator measurement. We used the Lambda-Mu-Sigma (LMS) method to establish reference equations for various spirometry parameters. We assessed model fit using mean absolute error (MAE), mean absolute percentage error (MAPE), and residual values (standard deviation), relative to established benchmarks such as GLI, ECSC, and NHANES III, to evaluate the applicability of our equations to high-altitude residents. Between June 2015 and August 2016, 3174 healthy subjects were included. The reference equations utilise age and height as independent variables, with improved accuracy achieved through spline functions. Our spirometry reference equations demonstrate minimal MAE, MAPE, and residual values (standard deviation) for most of the analysed spirometry parameters, stratified by gender. Our spirometry reference equations are more applicable to residents of high-altitude regions.