Serum eosinophil cationic protein (ECP): reference values in healthy nonatopic children

Background: Although serum ECP concentrations have been reported in normal children, there are currently no published upper cutoff reference limits fo r serum ECP in normal, nonatopic, nonasthmatic children aged 1-15 years. Methods: We recruited 123 nonatopic, nonasthmatic normal children attending the Royal Belfast Hospital for Sick Children for elective surgery and meas ured serum ECP concentrations. The effects of age and exposure to environme ntal tobacco smoke (ETS) on the upper reference limits were studied by mult iple regression and fractional polynomials. Results: The median serum ECP concentration was 6.5 mu g/l and the 95th and 97.5th percentiles were 18.8 and 19.9 mu g/l. The median and 95th percenti le did not vary with age. Exposure to ETS was not associated with altered s erum ECP concentrations (P=0.14). Conclusions: The 95th and 97.5th percentiles for serum ECP for normal, nona topic, nonasthmatic children (aged 1-15 years) were 19 and 20 mu g/l, respe ctively. Age and exposure to parental ETS did not significantly alter serum ECP concentrations or the normal upper reference limits. Our data provide cutoff upper reference limits for normal children for use of serum ECP in a clinical or research setting.