Background Two distinct, stable inflammatory phenotypes have been described in adults with asthma: eosinophilic and non-eosinophilic. Treatment strategies based on these phenotypes have been successful. This study evaluated sputum cytology in children with asthma to classify sputum inflammatory phenotypes and to assess their stability over time.

Methods Sputum induction was performed in 51 children with severe asthma and 28 with mild to moderate asthma. Samples were classified as eosinophilic (>2.5% eosinophils), neutrophilic (>54% neutrophils); mixed granulocytic (>2.5% eosinophils, >54% neutrophils); or paucigranulocytic (≤2.5% eosinophils, ≤54% neutrophils). Sputum induction was repeated every 3 months in children with severe asthma (n=42) over a 1-year period and twice in mild to moderate asthma (n=17) over 3–6 months.

Results 62 children (78%) had raised levels of inflammatory cells in at least one sputum sample. In the longitudinal analysis 37 of 59 children (63%) demonstrated two or more phenotypes. Variability in sputum inflammatory phenotype was observed in both the severe and the mild to moderate asthma groups. Change in phenotype was not related to change in inhaled corticosteroid (ICS) dose or asthma control, nor was it reflected in a change in exhaled nitric oxide (FE_NO). 24 children (41%) fulfilled the criteria for non-eosinophilic asthma on one occasion and eosinophilic on another. There were no differences in severity, asthma control, atopy, ICS dose or forced expiratory volume in 1 s between those who were always non-eosinophilic and those always eosinophilic.

Conclusion Raised levels of inflammatory cells were frequently found in children with asthma of all severities. Sputum inflammatory phenotype was not stable in children with asthma.