Comparison of Blood Eosinophil Numbers Between Acute Asthma and Stable Disease in Children with Preschool Wheeze

Background: Preschool wheezing is common and many children experience exacerbations and are well in between. Raised blood eosinophils in older children are associated with exacerbation-prone wheeze, but there are currently no biomarkers to predict near-future exacerbations in preschoolers. There is evidence suggesting that eosinophils are acutely activated during an exacerbation using urinary markers, however, it is unknown whether blood eosinophil numbers fluctuate between the time of an exacerbation and stable disease. Objective: To investigate whether, in children with preschool wheeze, blood eosinophil numbers are different during an acute wheezing episode compared with periods of stable disease. Methods: Blood samples were taken from children aged 10 months to 6 years, presenting with acute, doctor-diagnosed wheeze, and tested for absolute leukocyte differential cell numbers. A repeat blood sample was obtained in a subset of children after full recovery. Main Outcome Measure: Difference between blood eosinophil counts during an acute wheezing episode and after recovery (stable disease) was also obtained. Results: Eighty-five children participated in this study, with 68 recruited during an acute wheezing episode (median absolute blood eosinophil numbers 0.10 × 109/L [range 0.00–2.41]) and 17 healthy controls. There was no significant difference in absolute blood eosinophil numbers between the acutely wheezy children when compared with the controls (median 0.17 × 109/L range 0.00–0.83). Absolute blood eosinophil numbers during stable disease were significantly greater (median 0.43 × 109/L; range 0.12 × 1.25 × 109/L) compared with periods of exacerbation (median 0.11 × 109/L range 0.01–1.10) in 20 children in whom paired blood samples were available. Absolute blood lymphocyte numbers were also higher during periods of stable disease, whereas absolute blood neutrophil numbers were higher during the exacerbation. Conclusions: Greater numbers of blood eosinophils are present during stable disease compared with the exacerbation state. This is an important consideration when planning future studies using blood eosinophils as a biomarker in wheezy preschool children.