Induced sputum in interstitial lung diseases - A pilot study

Induced sputum with hypertonic saline has been suggested as a safer and cheaper alternative to bronchoalveolar lavage for evaluation of patients with interstitial lung diseases (ILD).

To evaluate the safety and feasibility of sputum induction in ILD and to compare sputum cellular profiles with paired bronchoalveolar lavage fluid results.

Twenty patients underwent sputum induction with 4.5% saline within 2 weeks of bronchoalveolar lavage. Total, differential cell counts and cellular viability were assessed. Wilcoxon test and Spearman's rank correlation coefficient were used and a p<0,05 was considered statistically significant.

From a total of 20 subjects (mean age 49.4±16.4 years, 70% male) a satisfactory sputum sample was obtained in 15 subjects (75%). Induction was stopped in one subject, due to a significant decrease in PEF. The cell profiles for induced sputum and bronchoalveolar lavage fluid (BALF) were different (P <.05), except for eosinophils, and there were no significant correlations between the two methods. Compared to sputum reference values there was an increase of lymphocytes (3.2% vs 0.5%) and eosinophils (1.4% vs 0.0%). Comparing sarcoidosis and hypersensitivity pneumonitis sputum, both diseases had an increase in lymphocytes (4.4 vs 3.9%), with a significant higher neutrophil count in hypersensitivity pneumonitis (65.4% vs 10.6% P <0.05), a finding also seen in BALF.

Induced sputum is feasible and safe in interstitial lung diseases. Although sputum cellular counts are not correlated with bronchoalveolar lavage fluid, sputum cellular profiles may help to distinguish different ILD.