Impact of race-neutral GLI reference equations in Northeast Asian patients with IPF

Background The Global Lung Function Initiative (GLI) has recently introduced race-neutral reference equations for pulmonary function tests, replacing traditional ethnic-specific equations. However, the clinical impact of this transition in Northeast Asian patients with idiopathic pulmonary fibrosis (IPF) remains unclear. Methods We evaluated the implications of switching from the ethnic-specific equations to the race-neutral GLI equations in 903 Korean patients newly diagnosed with IPF between 2005 and 2020. Per cent predicted values of forced vital capacity (FVC) and diffusing capacity for carbon monoxide (DLCO) were calculated using both equations and used to derive the baseline gender-age-physiology (GAP) index scores. We then compared the prognostic performance of GAP staging derived from each equation in predicting all-cause mortality. Additionally, we assessed the clinical impacts of 1-year absolute declines in FVC and DLCO % predicted, as determined by each equation. Results The race-neutral GLI equations yielded higher FVC % predicted and lower DLCO % predicted values compared with the ethnic-specific equations, resulting in GAP stage reclassification in 203 of 903 patients (22.5%), predominantly toward lower stages. Despite these differences, the agreement in GAP staging between the two equations was substantial (Cohen’s kappa 0.628) and their predictive performance for mortality did not significantly differ (C-index 0.686 vs 0.684; p=0.598). One-year absolute declines in FVC and DLCO % predicted were similarly associated with increased mortality, regardless of reference equation used. Conclusions In Northeast Asian patients with IPF, race-neutral GLI equations resulted in reclassification of GAP stage for some patients but did not affect the overall prognostic performance of the GAP index in predicting mortality.