To assess the sensitivity and specificity of serum eosinophil cationic
protein (ECP) in the diagnosis of asthma and evaluation of asthma sev
erity, we conducted a prospective study to compare parameters of asthm
a severity, peripheral blood eosinophilia, and serum ECP concentration
s in 88 children presenting to a university hospital outpatient clinic
with suspected (n=59) or recently diagnosed asthma (n=29). Serum ECP
correlated significantly (r(s)=0.676, P=0.0001) with peripheral eosino
phil counts, but only weakly with asthma severity (r(s)=0.21, P=0.046)
. Serum ECP was significantly higher in atopic children (25+/-11 mu g/
l) than in nonatopic children (16+/-15 mu g/l) (P=0.01). Bronchial hyp
erresponsiveness had no significant correlation (r(s)=-0.21, P=0.30) w
ith serum ECP. Lung function test results had no (peak flow) or only a
weak (FEV1) correlation with serum ECP, In distinguishing between chi
ldren with and without asthma or in assessing asthma severity, serum E
CP is not superior to the peripheral blood eosinophil count. The diagn
ostic sensitivity and specificity of ECP in serum for detecting sympto
matically active asthma, evaluated against the cutoff level of ECP in
serum of 16 mg/l, were 54% and 71%, respectively.