The relationship of serum-eosinophil cationic protein and eosinophil count to disease activity in children with bronchial asthma

Background. The serum-eosinophil cationic protein level (S-ECP) has been promoted as a biomarker of asthma that reflects the degree of bronchial eosinophilic inflammation. Patients and methods. To investigate whether S-ECP is indeed a clinically useful objective parameter, especially in mild or moderate chronic childhood asthma, we studied 100 outpatient children with chronic asthma symptoms (63 boys and 37 girls, aged three to 15 years, median of age eight) and 25 controls (12 boys and 13 girls aged three to 15 years, median of age eight). Symptom scores, lung function parameters and atopy were compared with S-ECP determined by commercially available tests and eosinophils measured by an autoanalyser. Results. Asthma symptom scores in the patient group ranged between one and 13 (median of 8), S-ECP between 2.1 and 75.6 mu g/l (median of 13.3 mu g/l), and eosinophils between 30/mu l and 2002/mu l (median of 314). Symptom scores and S-ECP were correlated significantly (P < 0.001) as were symptom scores and eosinophils (P = 0.001). S-ECPs were significantly higher in children with chronic asthma symptoms compared with non-asthmatic, non-atopic children (P = 0.005 for non-atopic chronic asthmatics and P < 0.001 for atopic asthmatics); similar results were found comparing eosinophils in these groups. There was no difference in S-ECP between atopic and non-atopic asthmatic children, but the 25 polysensitised asthmatic children especially with sensitisations to mite, pollen and pet allergens were found to have significantly higher S-ECP compared to 15 monosensitised children (P = 0.002). Similar results were found when correlating eosinophil numbers with atopy. Polysensitised (mite, pollen, pet) asthmatics had significantly higher eosinophil counts compared with monosensitised (pollen) asthmatics (P = 0.01); there was, however a better discrimination between atopic and nonatopic asthmatics (P = 0.001). Non-asthmatic, non-atopic controls had significantly lower eosinophil counts compared with asthmatics (P < 0.001 for both non-atopic and atopic asthmatics). No correlation between S-ECP or eosinophils and any of the lung function parameters measured (FEV1, FEV1/FVC, MEF50, airway resistance and ITGV) was found. Summary. Our data thus indicate that 1) S-ECP is higher than normal in children with asthma symptoms and correlates with asthma symptom score. 2) S-ECP is better correlated to symptom score than to lung function parameters especially in children with mild and moderate asthma symptoms. 3) Raised S-ECP appears to reflect the extent of allergen sensitivity and may also reflect current allergen exposure. 4) Similar correlations were seen when measuring eosinophil number by an autoanalyser instead of S-ECP. Conclusions. Although S-ECP and eosinophils are not diagnostic of asthma they are useful inflammation markers especially in the context of clinical studies. However, both methods are not yet suitable for use in daily practice because they require extensive procedures and special equipment.