Blood eosinophils associate with reduced lung function growth in adolescent asthmatics

BACKGROUND AND OBJECTIVE: Some children with asthma have low lung growth, putting them at increased risk for COPD later in life. However, it is currently not clear who will experience this adverse growth pattern. We therefore investigated the predictive role of blood eosinophils as a type 2 inflammation marker in lung growth, focusing on the presence and severity of asthma. METHODS: We investigated blood eosinophils and lung function growth (percentage of predicted values) using linear mixed models in children and adolescents from two longitudinal cohorts. One cohort was hospital‐based and consisted of asthmatic children at their first outpatient clinic visit after referral by the general practitioner (n = 133, mean age 9.8), while the second was a general population‐based birth cohort (PIAMA, asthma n = 52 and non‐asthma n = 433, mean age 8.1). The hospital‐based cohort had not been treated with inhaled corticosteroids (ICS) before referral. RESULTS: Subjects in the hospital‐based asthma cohort had more severe asthma compared with the asthmatic subjects in the population‐based cohort, defined by lower lung function levels and a higher prevalence of bronchial hyper‐responsiveness. In the asthma cohort, higher blood eosinophil numbers were associated with less growth in FEV(1) (estimated change in lung function per 1 unit increase in ln blood eosinophils (B): −0.66%/year (95% confidence interval (CI): −1.11 to −0.20, p < .01)) and FVC (B: −0.40%/year (95% CI: −0.75 to −0.05), p = .025)) during follow‐up in adolescence (min 7, max 17 years). These associations were not observed in the general population‐based birth cohort, regardless of asthma status during follow‐up (age 8–16). CONCLUSIONS AND CLINICAL RELEVANCE: Blood eosinophil counts in children with asthma not treated with ICS at referral were predictive of lower growth in FEV(1) and FVC during follow‐up in adolescence. Our findings indicate that this association is dependent on the degree of asthma severity. Future studies should address whether anti‐eosinophilic treatments preserve lung function growth in children with asthma.