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Background The Global Lung Function Initiative (GLI) 2022 reference equations introduced race neutral spirometry predictions that differ from the previously used GLI-2012 equations. While these equations aim to improve interpretation of lung function, their impact on physiological severity indices used in idiopathic pulmonary fibrosis (IPF), including the Gender–Age–Physiology (GAP) index, Distance–Oxygen–Gender–Age–Physiology (DO-GAP) index and the Composite Physiologic Index (CPI), remains unclear.Aim To compare GAP, DO-GAP and CPI calculated using GLI-2022 versus GLI-2012 and assess physiological and clinical implications.Methods Retrospective data were analysed from 721 white patients with IPF who performed spirometry, diffusing capacity for carbon monoxide (DLCO) and six-minute walk testing. Percent-predicted values were recalculated using GLI-2012 and GLI-2022 reference equations. GAP was derived from sex, age, FVC% and DLCO%. DO-GAP additionally incorporated exertional desaturation and six-minute walk distance. CPI was calculated as: 91 − (0.65 × DLCO%) − (0.53 × FVC%) + (0.34 × FEV1%). Paired t-tests assessed within patient differences in lung function and index values. GAP and DO-GAP stage reclassification was examined using McNemar test.Results Mean FVC% predicted was higher using GLI-2022 compared with GLI-2012 (77.2 ± 15.1% vs 74.2 ± 15.1%, p<0.001). Mean FEV1% predicted was also higher using GLI-2022 (83.1 ± 16.2% vs 77.9 ± 15.7%, p<0.001). Mean CPI was slightly lower under GLI-2022 (47.7 ± 11.7 vs 48.2 ± 11.5, p<0.001), and mean GAP score decreased (3.99 ± 1.25 vs 4.08 ± 1.26, p<0.001). Mean DO-GAP score was also slightly decreased under GLI-2022 compared with 2012 (7.02 ± 3.57 vs 7.11 ± 3.57 p<0.001). GAP stage remained unchanged in 692/721 (96.0%) patients; 27 patients were up staged and 2 down staged (McNemar p<0.001). DO-GAP stage remained unchanged in 709/721 (98.3%) patients; 11 were up staged and 1 down staged (McNemar p<0.001).Conclusion Recalculation using GLI-2022 produced small increases in FVC and FEV1 percent predicted and modest reductions in CPI and GAP values in white patients with IPF. Although statistically significant, these changes resulted in minimal stage reclassification for GAP and DO-GAP.