Induced sputum: opening a new window to the lung

The interest in sputum assessment as a non-invasive technique to retrieve cells and soluble material from the lung has increased and gained momentum during the last decade. As a marker of inflammation in airway diseases, induced sputum (IS) is a particularly promising procedure since it provides specific information on both the cellular and molecular constituents in inflammation. From 1950-1970, sputum cells had been examined on stained smears, with the procedure having been applied in both research and clinical settings. After having been recovered by spontaneous coughing, the cells were used to study lung cancer and respiratory infections and, later on, to diagnose Pneumocystis carinii pneumonia in patients infected with human immuno-deficiency virus (HIV). The method was widely improved upon by the induction of Sputum with aerosol of hypertonic saline and then extended to become part of the assessment of airway inflammation in bronchial asthma and chronic obstructive pulmonary disease (COPD). It was recently shown that IS can be used to study interstitial lung diseases (ILD) and, more specifically, pneumoconiosis, sarcoidosis, non-granulomatous ILD and occupational lung diseases. In light of the fact that immunologic and functional bronchopulmonary abnormalities may be present in up to two-thirds of patients with Crohn's disease, we studied the use of IS in this condition as well. This review analyzes the value of IS and its present applications in pulmonary medicine.