Implications of Global Lung Function Initiative Spirometry Reference Equations in Northeast Asian Patients With COPD.

Background: Accurate spirometry interpretation is critical in the diagnosis and management of COPD. With increasing efforts for a unified approach by the Global Lung Function Initiative (GLI), this study evaluated the application of race-specific 2012 GLI and race-neutral 2022 GLI reference equations compared with Choi's reference equations, which is derived and widely used in South Korea, for spirometry interpretation in Northeast Asian patients with COPD.

Research question: What are the effects of applying race-specific 2012 GLI, race-neutral 2022 GLI, and Choi's reference equations on the diagnosis, severity grade, and clinical outcome associations of COPD?

Study design and methods: Serial spirometry data from the Korea COPD Subgroup Study (KOCOSS) consisting of 3,477 patients were used for reanalysis using 2012 GLI, 2022 GLI, and Choi's reference equations. The COPD diagnosis and severity categorization, associations with disease manifestations and health outcomes, and longitudinal trajectories of lung function were determined.

Results: Although there was strong concordance in COPD diagnosis comparing 2012 GLI, and 2022 GLI reference equations with Choi's reference equations, a notable portion of patients were reclassified to milder disease severity (17.0% and 23.4% for 2012 GLI and 2022 GLI reference equations, respectively). Relationships between FEV₁ % predicted values calculated using 2012 GLI, 2022 GLI, and Choi's equations with clinical outcomes including dyspnea severity, exercise capacity, health-related quality of life, and frequency of exacerbations remain consistently significant. Similar annual decline rates of FEV₁ and FVC % predicted were observed among the reference equations used, except for slower annual decline rate of FEV₁ in Choi's equation compared with 2022 GLI race-neutral equation.

Interpretation: Application of GLI reference equations for spirometry interpretation in Northeast Asian patients with COPD has potential implications on disease severity grade for clinical management and trial participation, and maintains consistent significant relationships with key disease outcomes.