Eosinophil cationic protein (ECP) in schoolchildren living in a mountainous area of Norway:: a population-based study of ECP as a tool for diagnosing asthma in children with reference values

Background: Most previous studies on eosinophil cationic protein (ECP) have been performed on carefully selected groups of asthmatic patients. Few studies based upon population cohorts have been reported. The primary objective of the present study was to assess the usefulness of serum eosinophil cationic protein (s-ECP) in the diagnosis of asthma in schoolchildren and determine reference values based on measurements in healthy children. Methods: The population consisted of 216 schoolchildren (aged 7-16 years) who in a previous questionnaire had reported asthma or asthma-like symptoms and a control group. The questionnaire study comprised the entire population of schoolchildren in Upper Hallingdal. After clinical assessment, blood samples, and skin prick tests, these subjects were then reclassified into four groups: atopic and nonatopic asthmatic and nonasthmatics. S-ECP was assessed in relation to atopy, asthma severity, allergen exposure, and sex. Results: The asthma group (n = 105) had significantly higher mean s-ECP level than the nonasthma group (n=111) (13.3 vs 8.3 mug/l, P<0.001), with no significant difference between atopic asthmatics and atopic nonasthmatics. Mean s-ECP levels in children with mild, moderate, or severe asthma were 12.1, 18.5, and 12.2 <mu>g/l, respectively. The children with animal dander allergy demonstrated higher levels of s-ECP than children without this allergy (12.9 vs 9.1 mug/l, P = 0.001). The upper reference limit (determined as the 95th percentile in healthy children) of 19.1 mug/l, showed low sensitivity (24%) and high specificity (93%) for the diagnosis of asthma. The positive and negative likelihood ratios for the asthma diagnosis were found to be 3.2 and 0.83, respectively. Conclusions: The highest s-ECP values were found among children with moderate asthma. Animal dander allergy resulted in elevated s-ECP. However, mean values were still below the reference value of 19.1 mug/l, and the sensitivity was low, suggesting that s-ECP is not a useful parameter for diagnosing asthma in population-based studies.