Induced sputum in interstitial lung diseases: novel insights in the diagnosis, evaluation and research

The search for noninvasive procedures of retrieving cells and soluble material from the lung has gained momentum over the past few years. Induced sputum (IS) by inhalation of hypertonic saline solution is a noninvasive technique used to collect cellular and soluble material from lung airways. During the past decade, this method has been widely used to assess airway inflammation in asthma and chronic obstructive disease, since it produces reliable results and compares favorably to other invasive techniques, such as biopsy and bronchoalveolar lavage fluid. However, recent attention has been paid to its efficacy in the evaluation of interstitial lung diseases. Recent research in this area clearly showed that IS analysis could give extensive information regarding the inflammation in pulmonary sarcoidosis, such as the lymphocytic cell count, the CD4+/CD8+ ratio and the Th1 immunologic response. The CD4+/CD8+ ratio recovered from lymphocytes from IS is as useful as the same value retrieved from examination of lymphocytes recovered from bronchoalveolar lavage fluid for clinical use. The above findings suggest that integrating IS procedure in the diagnosis, evaluation, follow-up and research in patients with pulmonary sarcoidosis is necessary. Besides sarcoidosis, the review of the current literature in other interstitial lung diseases showed that IS could provide us with useful information regarding inflammatory molecules, but cannot fully replace more invasive techniques. This review analyzes the applications of IS in the assessment of fibrotic and granulomatous diseases such as sarcoidosis and extrinsic allergic alveolitis, idiopathic pulmonary fibrosis, connective tissue disorders, occupational lung diseases and other systemic diseases.