Abnormal spirometry in pediatric asthma – real-life application of the updated ATS/ERS guidelines.

<bold>Background</bold> We applied the updated ATS/ERS guidelines in a nationwide specialist-care cohort to explore abnormal lung function, prevalence of moderate/severe airway obstruction and associations with asthma morbidity. <bold>Methods</bold> Pre- and post-bronchodilator (BD) FEV1, FEV1/FVC, Asthma Control Test (ACT) scores and data on asthma treatment were extracted from the Swedish National Airway Register from 3301 asthmatic children (age 6-17y). GLI reference equations were used, abnormal values identified by lower limits of normal (LLN), i.e., z-score <-1.65, and moderate/severe obstruction by z-score <-2.51. Bronchodilator response (BDR) was calculated using ((postBD – preBD) / predicted value) x 100 and >10% was considered positive. <bold>Results</bold> The mean (standard deviation) FEV1 and FEV1/FVC z-scores were −0.65 (1.1) and −0.57 (1.1) preBD and −0.25 (1.1) and 0.01 (1.1) postBD. The proportions of children with preBD FEV1<LLN or FEV1/FVC<LLN were 16.5% and 17.5%, respectively, whereas the proportions were 9.2% and 6.2% postBD. Among all children, 26.4% had at least one abnormal spirometric value preBD (FEV1<LLN or FEV1/FVC<LLN), and 7.5% had both. In preBD analysis, moderate/severe obstruction was prevalent among 25.5% and 22.2% of the children with FEV1<LLN and FEV1/FVC<LLN, respectively. Having both FEV1<LLN and FEV1/FVC<LLN preBD was associated with older age, ACT<20, GINA step 3-5 treatment and a positive BDR (p<0.001 for all comparisons). <bold>Conclusion</bold> In this nationwide specialist-care asthma cohort, 26% of the children had at least one abnormal spirometric value preBD, the majority had mild obstruction and abnormal spirometry associated with uncontrolled asthma, more treatment and positive BDR.