Eosinophils and eosinophil-derived proteins in children with moderate asthma.

Laboratory parameters can contribute to the diagnosis of asthma, which is often a difficult procedure in paediatric patients. The aim of this study was to investigate the value of eosinophil cationic protein (ECP) and eosinophil-derived neurotoxin (EDN) in the diagnosis of paediatric asthma. The number of eosinophils, serum ECP and EDN, and urinary EDN were determined in 22 children with stable, allergic asthma, aged 4-14 yrs, and in 17 age-matched healthy controls. Symptoms were monitored, the peak expiratory flow rate (PEFR) was recorded in the younger children, and lung function tests (forced expiratory volume in one second (FEV1) and the provocative concentration of histamine causing a 20% fall in FEV1 (PC20)) were performed in the older children. None of the asthmatic children had respiratory symptoms. PEFR was not significantly different in asthmatic children compared to controls. The FEV1 % predicted was significantly lower compared to controls. The number of eosinophils, serum ECP and EDN, and urinary EDN were significantly higher in asthmatic children compared with controls. After correction of serum ECP and EDN, and urinary EDN for the number of eosinophils, the differences between patients and controls disappeared. The nocturnal PEFR and the FEV1 were significantly related to urinary EDN. The results suggest that serum and urinary concentration of eosinophil-derived proteins can be determined instead of the number of eosinophils to support the diagnosis of asthma in childhood. The urinary concentration of eosinophil-derived neurotoxin can be especially valuable in young children, because in this age group quantification of lung function cannot be performed and blood sampling can be difficulty.