The association between persistent eosinophilia and asthma in childhood is independent of atopic status

Background Although peripheral blood eosinophilia is associated with risk of asthma, the relation with atopy has not been established. Objective To assess the relationship between eosinophils and chronic asthma in childhood, and to determine the factors associated with eosinophil levels over time. Methods Percent eosinophils/300 white blood cell (WBC) count (‘eos’) was measured at 9 months, 6 years and 11 years in subjects participating in the prospective Tucson Children's Respiratory Study. Children were classified based on the number of measurements in which they had low (≤ 2%) or high (> 5%) eosinophils, as follows: (1) Persistently low eos (n = 130); (2) Low eos (intermittently low or consistently moderate, but never high, n = 317); (3) Intermittently high eos (n = 192); and (4) Persistently high eos (n = 17). Only children with ≥ 2 eos measurements were included in the analysis. Chronic asthma was defined as medical doctor (MD)‐diagnosed asthma with reports of wheezing during the previous year, on ≥ 3 questionnaires completed between 2 and 13 years of age. Children with at least one positive skin prick test (SPT; ≥ 3 mm) at age 6 or 11 were considered ‘atopic’. Results Chronic asthma was linearly related to longitudinally ascertained eosinophils (trend χ2P