Significance of the eosinophil cationic protein/eosinophil count ratio in asthmatic patients: its relationship to disease severity

Background: Serum levels of eosinophil cationic protein (ECP) may reflect the degree of bronchial inflammation in patients with asthma, but its clinical value as a parameter for monitoring asthma remains controversial. Objective: We measured the ratios of the serum ECP concentrations to peripheral blood eosinophil counts (ECP/Eo ratio) in patients with asthma and evaluated the correlation between these ratios and individual asthma severity. Methods: The serum ECP concentrations and peripheral blood eosinophil counts were measured by radioimmunoassay and an autoanalyzer, respectively. Each patient with asthma was in remission at the time the serum specimen was obtained. An overall evaluation of asthma severity for each patient was determined by the frequency and severity of asthma attacks and by clinical scores. Results: The ECP/Eo ratio in patients with severe asthma was significantly higher than in those with mild asthma. However, serum ECP concentrations and peripheral blood eosinophil counts were not different among the patients with mild, moderate, or severe asthma. The ECP/Eo ratios correlated significantly with the monthly average of the clinical scores, but the serum ECP concentrations did not correlate with the monthly average of the clinical scores. The ECP/Eo ratios were also increased in patients with more severe asthma whose serum IgE concentrations and peripheral eosinophil counts were not elevated. Conclusions: The ECP/Eo ratio may be useful in assessing asthma severity; however, the serum ECP concentration or peripheral blood eosinophil count is not useful.