Spirometry results and proportion of children with spirometry data below the lower limit of normal (LLN) or above the upper limit of normal (ULN)

BoysGLI versus ZapletalGirlsGLI versus ZapletalBoys versus girls p-value#
Subjects n215227
Children aged <6 years31.632.2
Height cm131.2±19.7129.5±19.8
BMI kg·m−217.2±3.117.0±2.8
BMI z-score0.37±1.280.41±1.30
Mean z-scores
Zapletal [3, 4]
Distribution of z-scores<LLN+>ULN§<LLN+>ULN§Boys versus girls p-value
Zapletal [3, 4]

Data are presented as mean z-scores±sd or %, unless otherwise stated. BMI: body mass index; FVC: forced vital capacity, FEV1: forced expiratory volume in 1 s. #: comparisons of z-score difference performed by Student's t-test. Comparison of proportions of subjects relative to the LLN and ULN were performed by Chi-squared test or Fisher's exact test except when observed frequencies were <5. Means were compared to 0 using paired Student's t-tests and sds were compared to 1 using Chi-squared tests for variance; : Rolland-Cachera et al. [9]; +: <−1.645 z-score value ; §: >1.645 z-score value. *: p<0.05; **: p<0.01; ***: p<0.001.