[Cut-off point for a positive bronchodilation test]

To determine bronchodilation in healthy children aged 7-14 years in order to establish the value defining a positive bronchodilation test.

We performed a cross-sectional study in healthy, nonsmoking schoolchildren aged 7-14 years in the city of Huesca (Spain). The sample (n 145) was representative of the pediatric population aged 7-14 years (N 4,272). Health was determined through a validated questionnaire. Expired carbon monoxide was measured with a Micro III Smokerlyzer EC50(R). Forced basal and post-bronchodilation spirometry (0.2 mg of inhaled salbutamol with a Babyhaler(R) chamber) was performed with a Vitalograph spirometer mod. 2120(R). Forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC, forced expiratory flow at 24-25 % of forced vital capacity (FEF25-75 %) and peak expiratory flow (PEF) were measured. To establish whether increments in the variables followed normal distribution, the Kolmogorov-Smirnov test (Lilliefors modification) and histograms were used. The relationship between increases in FEV1 and the variables in the questionnaire was analyzed using Student's t-test (qualitative variables) and Pearson's correlation (quantitative variables). To evaluate the reliability of the test, Spearman's non-parametric correlation coefficient and dispersion graphs were used.

The percentage increase in FEV1 compared with the theoretical value was: mean (SD), 3.97 (2.65); 95 % percentile, 8.87 %; and 97.5 percentile, 10.25 %. The percentage increase in FEV1 compared with the previous value was: mean: 3.99 (2.63), 95-percentile: 8.43 %; and 97.5 percentile: 10.14 %.

In children aged 7-14 years, increases of greater than 9 % above the theoretical or previous FEV1 value define the bronchodilation test as positive.