CHANGES IN SPUTUM COMPOSITION DURING SPUTUM INDUCTION IN HEALTHY AND ASTHMATIC SUBJECTS

Background Induced sputum is increasingly used to characterize the cel lular and biochemical composition of the airways. Objective We studied whether the composition of induced sputum is different between sample s obtained sequentially during one sputum induction. Methods Subjects with mild asthma (n = 7) or healthy subjects (n = 6) produced sputum d uring and after three consecutive 10 min periods of hypertonic saline inhalation. Samples were analysed separately for the three periods. To determine the reproducibility of the cellular composition, sputum ind uction was repeated on another two days. Results The mean percentage o f neutrophils decreased significantly (P<0.01) during sputum induction in asthmatic (36.9, 29.8, 16.3%) and healthy subjects (43.6, 17.2, 18 .0%). Correspondingly, percentages of macrophages increased and percen tages of eosinophils were 4.9, 3.5, and 3.7% in the asthmatic and 0.6, 0.7, and 0.5% in the healthy subjects, without significant change ove r the three periods; mean eosinophil numbers were significantly higher in the subjects with asthma (P < 0.05). Reproducibility of percentage cell counts did not markedly depend on sampling periods in terms of c oefficients of variation. The concentration of eosinophil cationic pro tein decreased in both groups during sputum induction (P < 0.01), geom etric mean values being 579, 143, 57.4 mu g L-1 in the asthmatic and 1 30, 47.3, 28.4 mu g L-1 in the healthy subjects. Similar changes were seen for lactate dehydrogenase. Conclusion The separate analysis of in duced sputum from three consecutive sampling periods of a single induc tion procedure demonstrated significant changes in their cellular and biochemical composition, both in healthy and mild asthmatic subjects.