Serum Eosinophil Cationic Protein (ECP) in Chronic Asthma. Relationship to Spirometry, Flow-volume Curves, PC20, and Exacerbations

Serum ECP was measured in a double-blind study in relation to spirometry, flow-volume curves, and histamine PC20 (30-s tidal breathing method, normal value > 32 mg ml-1) in 20 chronic asthmatic patients (five male), mean age 48.9 yr (SD 11.0), once a month and at additional visits due to acute exacerbations over a 6-month period. All patients were on maintenance inhaled corticosteroid therapy. Serum ECP was considered elevated at > or = 20 micrograms l-1. ECP showed significant negative correlations with lung function, especially when ECP was elevated (45/143 observations): r = -0.48, -0.48, and -0.49 for respectively FEV1, PEF, and MMEF (all at baseline and as % predicted, P = 0.001), the best correlation being with FEV1/FVC ratio (r = -0.61, P < 0.001). PC20 only had a weak overall correlation with ECP (r = -0.21, P = 0.015). Eosinophilia at > or = 0.400 x 10(9) cells l-1 (38/143 observations) did not show any significant correlations with the lung function variables. The patients were subdivided into three groups according to exacerbations. Group A consisted of seven patients with suspected infectious exacerbations (mean 1.4), group B of six patients with suspected inflammatory exacerbations (mean 3.2), and group C of seven patients who did not experience any symptomatic exacerbations. A significant difference in mean ECP was found between group B and A (33.1 vs. 10.2, P = 0.003). Group B also differed significantly from group A with respect to lung function and PC20, but not to atopy, lung function and PC20 being lower and variability higher in group B. The findings of this study suggest that serum ECP is a sensitive marker of inflammatory airflow obstruction in chronic asthma. Elevated ECP seems to denote patients at risk from inflammatory exacerbations, resulting in practical implications for the therapeutic management of chronic asthma.