CHANGES IN SPUTUM COMPOSITION BETWEEN 2 INDUCTIONS PERFORMED ON CONSECUTIVE DAYS

Background - Sputum induction is a noninvasive method for obtaining ce llular and biochemical material from the airways and appears to be par ticularly suited for repeated testing. However, it has not been clarif ied whether repeated inductions lead to a change in sputum composition . The aim of this study was to compare induced sputum results between two inductions performed 24 hours apart.Methods - Ten subjects with mi ld asthma and 19 healthy subjects were included. Sputum was obtained d uring three consecutive 10 minute periods of hypertonic saline inhalat ion. Samples were analysed separately for the three inhalation periods . Corresponding pooled values were computed, taking into account total cell numbers of each inhalation period. Results - In the three consec utive inhalation periods mean (SE) percentages of neutrophils increase d from 29.2 (4.2)%, 22.0 (4.6)% and 14.5 (2.9)% on day 1 to 43.1 (5.3) %, 34.8 (5.5)% and 25.7 (5.3)% on day 2 in healthy subjects and from 2 1.3 (4.3)%, 24.1 (5.9)% and 15.9 (3.7)% to 35.9 (6.9)%, 30.7 (7.1)% an d 31.8 (6.5)% in asthmatic subjects. This parallel shift corresponded to a mean (95% CI) increase in the pooled percentages of neutrophils o f 17.4 (11.6 to 23.3)% in healthy and 14.6 (1.2 to 28.0)% in asthmatic subjects. In contrast to neutrophils, the percentage of macrophages d ecreased from day 1 to day 2, while eosinophil and lymphocyte percenta ges did not change significantly. Conclusion - These results suggest t hat the induction procedure itself causes a change in the composition of sputum detectable after 24 hours. This effect has to be taken into account when repeated sputum induction is performed.