Sputum eosinophil count in a large population of patients with mild to moderate steroid-naive asthma: distribution and relationship with methacholine bronchial hyperresponsiveness

Background: Although airway eosinophilia is seen as a cardinal feature of asthma, data eosinophilia are still lacking on the proportion of the asthma group exhib iting raised airway eosinophilia. This study aimed to assess the distribution of sputum eosinophil count and its relationship with methacholine bronchial hyperresp onsiveness in mild to moderate steroid-naive asthmatic people. Methods: Sputum was induced by inhalation of hypertonic sali ne (NaCl 4.5%) in 118 mild to moderate steroidnaive asthmatic people consecutively recruited from our outpatient clinic, and in 44 healthy people. T he asthma group was selected on the basis of an forced expira tory volume in 1 s (FEV 1) of > 70% predicted, and a provocative methacholine concentration causing a fa ll of 20% in FEV 1 (PC 20 methacholine; PC 20 M) ≤ 16 mg/ml. Results: In the asthma group, the median (range) of the perc entage and the absolute values of sputum eosinophils were 4.8% (0-75) and 38 10 3 /g (0-14 191), respectively, vs 0% (0-2.3) (P 2%). In the asthma group, multiple regression analysis followed by a s tepwise procedure revealed that sputum eosinophil c ount was significantly and inversely associated with PC 20 M accounting for 16% of its total variance ( P < 0.001) while neutrophil counts positively related to PC 20 M accounting for 4% of total variance ( P < 0.05). By contrast, no significant relationship was found between either e osinophil or neutrophil counts and the slope of for ced vital capacity (FVC) vs FEV 1 from the methacholine challenge. Conclusions: We conclude that two-thirds of people in the mild t o moderate asthma group had increased sputum eosinophilia, which plays a limited role in determi ning the degree of methacholine airway hyperresponsiveness.