Evaluation of spirometry reference equations among healthy Jordanian adults: a comparative analysis of Jordanian and the global lung initiative equations

Accurate spirometry interpretation requires reference equations tailored to the target population. This study evaluated the performance and diagnostic agreement of the locally developed 2018 Jordanian equation and the Global Lung Initiative (GLI) global (2022), GLI-2012 Caucasian, and GLI-2012 Other/Mixed equations among healthy adult Jordanians. In this cross-sectional study, healthy nonsmoking Jordanian adults aged ≥18 years were recruited from various regions. Spirometry and anthropometric data were collected. Each equation’s suitability was assessed using mean z-score deviations from zero and standard deviations from one (via t-tests and chi-square tests). Linear and quantile regressions examined relationships between anthropometrics and lung function. Diagnostic agreement was evaluated using Cohen’s kappa and frequency of classification shifts. Among 799 participants (400 males), the Jordanian equation showed the best fit, with mean z-scores closest to zero and standard deviations near one. GLI global (2022) and GLI-2012 equations showed significant deviations (<i>p</i> &lt; 0.001), mainly due to age-related bias. Agreement was highest between GLI global (2022) and GLI-2012 Other/Mixed; GLI-2012 Caucasian classified the fewest as normal. The Jordanian equation provided better accuracy than GLI equations. Its use in practice may reduce misclassification and improve respiratory disease management, underscoring the value of population-specific standards.