Pulmonary function of healthy Korean children from three independent birth cohorts: Validation of the Global Lung Function Initiative 2012 equation

Background and Objective: Global Lung Function Initiative (GLI) 2012 equations were developed to resolve the age-related disparity in interpreting spirometry results. Local validation of the equation is needed, especially in Northeast Asian children. This study evaluated the GLI equation in Korean children. Methods: Spirometry indices (FEV1, FVC, FEV1/FVC, and FEF25%–75%) and clinical information were gathered from three population-based birth cohorts. Predicted GLI reference values and z scores of spirometry results were calculated for 1239 healthy children. The mean, standard deviation of z scores were compared with the expected 0 and 1. Probabilities of falling below the lower limit of normal (LLN) (z score: −1.64) were compared with the expected value 5%. GLI z scores were assessed according to low (<−2), normal (≥−2 and ≤2), and high (>2) BMI z score groups. Results: Mean z scores significantly differed from 0 for FEV1/FVC in males (mean [95% confidence interval]: 0.18 [0.08, 0.27]) and forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) in females (−0.23 [−0.31, −0.15] and −0.26 [−0.36, −0.16], respectively). The standard deviation was larger than 1 for all variables in males and FVC and FEV1/FVC in females. The probability of falling below the LLN was significantly larger than 5% for FEV1 (12.13% [9.64, 14.77]), FVC (15.86% [13.06, 18.81]), and forced expiratory flow at 25%–75% of forced vital capacity (FEF25%–75%) (7.31% [5.29, 9.49]) in males and FVC (11.91% [9.40, 14.60]) in females. FEV1 and FVC z scores increased across low to high body mass index (BMI) groups, and FEV1/FVC decreased from low to high BMI groups. Conclusion: GLI equations marginally differ from real-world values, which should be considered by pulmonologists in practice or research.