Circadian variation of urinary eosinophil protein X in asthmatic and healthy children

Background: It is suggested that urinary eosinophil protein X (EPX) is a noninvasive tool to monitor bronchial inflammation in asthmatic children. However, circadian variation of the number and activation of eosinophils might possibly influence urinary EPX excretion. Objective: Measurements of urinary EPX (radioimmunoassay) were used to investigate circadian variation of eosinophilic activation and to monitor bronchial inflammation in children with asthma before and after treatment with corticosteroids. Methods: Urinary EPX excretion (μg/mmol creatinine) was measured in the morning and afternoon in 22 stable asthmatics and in 16 nonatopic, nonasthmatic controls to investigate circadian variation. Additionally, EPX excretion in the afternoon was analysed in 21 children with chronic asthma before and after 6 weeks of treatment with inhaled corticosteroids, and in seven children within 24 h of admission due to an asthma exacerbation and again 3 months after discharge. Results EPX excretion in the first morning urine sample of the day compared with the afternoon urine sample was significantly higher both in children with asthma (n = 22; mean ± standard deviation: 179.7 ± 97.3 vs 60 9 ± 40.7 μg/mmol creatinine, P = 0.0001) and in nonatopic nonasthmatic controls (n = 16; 114.5 ± 57.1 vs 53.4 ± 29.0 μg/mmol creatinine, P = 0.0001). EPX excretion decreased significantly after 6 weeks of anti-inflammatory treatment in the group of children with chronic asthma (n=21; 124.7 ± 84.6 vs 87.5 ± 61.9 μg/mmol creatinine, P = 0.02) and in the group of children with an acute asthma exacerbation 3 months after discharge (n=7; 233.2 ± 174.5 vs 75.8 ± 59.5 μg/mmol creatinine, P = 0.02). Conclusion: This study suggests a circadian variation of EPX excretion in children with asthma and in nonatopic, nonasthmatic controls. Measurement of EPX excretion is helpful monitoring therapy in asthmatic children if circadian variation is considered.