Study objectives: Sputum induction (SI) is a noninvasive tool for sampling inflamed airways. The purpose of this study was to determine the optimal duration of collection in patients with cystic fibrosis (CF). The hypothesis was that the duration of SI collection would quantitatively and qualitatively alter the content of the induced sputum.
Methods: In 10 clinically stable patients with CF (mean +/- SD age, 28 +/- 7 years; mean FEV(1), 2.6 +/- 0.7 L), SI was performed with 3% hypertonic saline solution at five time points over 20 min.
Results: SI was well tolerated, with an average maximum fall in FEV(1) of 7 +/- 7%. The sample volumes, urea concentrations, interleukin-8 concentrations, total cell counts, and nonsquamous cell counts remained constant (p > 0.05). The percentage of neutrophils decreased from 89 +/- 5% to 86 +/- 4% (p = 0.03), and the percentage of alveolar macrophages increased 5 +/- 2% to 8 +/- 4% (p < 0.01). The mean quantitative microbiological counts of nonmucoid Pseudomonas aeruginosa and Staphylococcus aureus decreased over the 20-min time period each by half a log (p = 0.05 and p < 0.01, respectively). Surfactant protein-A concentration increased from 1.6 +/- 0.3 to 2.4 +/- 0.4 ng/mL (log(10); p < 0.001).
Conclusions: We conclude that aliquots of induced sputum are similar in clinically stable patients with CF during 4-min intervals, although there is more alveolar sampling after 20 min. When induced-sputum samples are fractionated for research monitoring of inflammatory or microbiologic indexes, power calculations accounting for these variations over time are required.