Cellular profiles of induced sputum in children with stable cystic fibrosis: comparison with BAL

Abstract

Neutrophil-dominated endobronchial inflammation is a major characteristic of cystic fibrosis (CF) and there is increasing demand for easy-to-perform noninvasive monitoring for prediction and intervention. Fourteen stable paediatric CF patients (8-17 yrs; mean forced expiratory volume in one second 86.7% of the predicted value) were investigated once by fractional bronchoalveolar lavage (BAL) and by sputum induction on three occasions, 2-6 weeks apart. Sputum was induced by consecutive 10-min inhalations of 3, 4 and 5% saline. CF sputum cellular profiles were compared with BAL fluid cell counts and samples from age-matched healthy children, and between different time points to assess reproducibility. Adequate sputum was recovered on >95% of occasions. In all sputum fractions, CF patients showed higher neutrophil counts than healthy children. Neutrophil percentages were highest in the first BAL fraction (median 92%), followed by sputum, in which the percentages decreased in consecutive fractions (72, 66 and 64%), whereas counts were lowest in the pooled BAL fraction (53%). Increasing percentages of macrophages mirrored the decreases in neutrophil percentage. Results of sputum induction at different time points in the CF patients showed good reproducibility and nonoverlap with counts from healthy children. In conclusion, the results of sputum induction in children with mild stable cystic fibrosis adequately describe airway inflammation by providing cellular profiles with lower relative neutrophil counts than in the first ("bronchial") bronchoalveolar lavage fraction and higher relative neutrophil counts than in subsequent pooled ("more peripheral") bronchoalveolar lavage fractions.