Evaluation of serum eosinophilic cationic protein as a marker of disease activity in chronic asthma.

Background: Serum eosinophil cationic protein (ECP) has been promoted as a direct marker of eosinophilic inflammation of the bronchi, especially helpful in patients with asymptomatic asthma.

Objective: To evaluate serum ECP against indirect clinical markers of disease activity, we compared symptom score, bronchial obstruction, bronchial responsiveness, and blood eosinophil counts with serum ECP levels in children with symptomatic and asymptomatic chronic asthma and assessed ECP in others with allergic rhinitis alone.

Methods: Twenty-four children with symptomatic asthma, 10 children with asymptomatic asthma, and 16 children with allergic rhinitis were studied. Measurements were made by standardized symptom questionnaire, spirometry, inhalation challenge with histamine or methacholine, blood eosinophil counts, and radioimmunoassay of serum ECP.

Results: There was no difference in serum ECP levels between the symptomatic asthma, asymptomatic asthma, or rhinitis groups, and most values were within the normal range. Activated eosinophil counts were higher in subjects with symptomatic asthma than in those with asymptomatic asthma but not in subjects with rhinitis. Serum ECP correlated with eosinophil counts (p < 0.01) but not symptom score, forced expiratory volume in 1 second (FEV1), forced expiratory flow, mid-expiratory phase (FEF25-75), or provocative concentration causing a 20% fall in FEV1 (PC20). Symptom scores correlated with PC20 (p < 0.005) and FEF25-75 (p < 0.01).

Conclusions: Serum ECP is a poor indicator of disease activity in chronic asthma and cannot differentiate bronchial from nasal inflammation.