[Sensitivity of sputum eosinophil cationic protein level for monitoring asthmatic patients with normal peak expiratory flow]

Abstract

Previous studies have shown that eosinophils and eosinophil cationic protein (ECP) levels in the sputum of patients with asthma closely reflect inflammatory activity of the bronchial mucosa. We examined whether the ECP level or eosinophil count in induced sputum provides information useful in determining whether to taper the dose of medications or to terminate treatment especially with inhaled corticosteroids in patients with well controlled asthma. We studied 15 adults with asthma who consistently maintained a peak expiratory flow (PEF) value within 80% or more of their predicted value (green zone) for at least 4 weeks with no asthmatic symptoms. All patients underwent at least two hypretonic saline inhalation tests. Forty sputum samples were obtained for evaluation of cell count and ECP level. Before the tests, patients were requested to record asthmatic symptoms, medications received, and morning and evening PEF values in a diary for more than 3 months. The relations among clinical and laboratory variables, including symptoms scores, medication scores, asthma scores (= symptom scores + medication scores). PEF values, forced expiratory volume (FEV1.0) during the test, and sputum eosinophil count or sputum ECP, were analyzed. The sputum ECP level correlated significantly with the percentage of eosinophils in the sputum (rs = 0.783). There were also significant correlations between the sputum ECP level and the mean weekly symptom scores (rs = 0.500-0.510), medication scores (rs = 0.510-0.540), and asthma scores (rs = 0.509-0.548). However, there were no significant correlations among sputum ECP level, mean morning PEF or evening PEF, daily variation in PEF, and FEV1.0. We conclude that the sputum ECP level is a sensitive laboratory variable useful in monitoring the presence of eosinophilic inflammation in the bronchial mucosa of patients with bronchial asthma, especially those who have mild or no symptoms with normal PEF.