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

Background It is suggested that urinary eosinophil protein X (EPX) is a non invasive tool to monitor bronchial inflammation in asthmatic children. Howe ver, circadian variation of the number and activation of eosinophils might possibly influence urinary EPX excretion. Objective Measurements of urinary EPX (radioimmunoassay) were used to inves tigate circadian variation of eosinophilic activation and to monitor bronch ial inflammation in children with asthma before and after treatment with co rticosteroids. Methods Urinary EPX excretion (mu g/mmol creatinine) was measured in the mo rning and afternoon in 22 stable asthmatics and in 16 nonatopic, nonasthmat ic controls to investigate circadian variation. Additionally, EPX excretion in the afternoon was analysed in 21 children with chronic asthma before an d after 6 weeks of treatment with inhaled corticosteroids, and in seven chi ldren within 24 h of admission due to an asthma exacerbation and again 3 mo nths 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 mu g/mmol creatinine, P = 0.0001) and in nonatopic nonasthmatic cont rols (n = 16; 114.5 +/- 57.1 vs 53.4 +/- 29.0 mu g/mmol creatinine, P = 0.0 001). EPX excretion decreased significantly after 6 weeks of anti-inflammat ory treatment in the group of children with chronic asthma (n = 21; 124.7 /- 84.6 vs 87.5 +/- 61.9 mu g/mmol creatinine, P = 0.02) and in the group o f children with an acute asthma exacerbation 3 months after discharge (n = 7; 233.2 +/- 174.5 vs 75.8 +/- 59.5 mu g/mmol creatinine, P = 0.02). Conclusion This study suggests a circadian variation of EPX excretion in ch ildren with asthma and in nonatopic, nonasthmatic controls. Measurement of EPX excretion is helpful monitoring therapy in asthmatic children if circad ian variation is considered.