Induced sputum as a diagnostic tactic in pulmonary diseases.

The induced sputum technique allows sampling of the airways in a non-invasive manner and thus offers a unique opportunity to identify biomarkers of potential clinical utility in respiratory medicine. Sputum cells were originally examined in stained smears and the procedure was applied in both research and clinical settings from the 1950s through the 1970s. The cells, recovered from spontaneous coughing, were used to study lung cancer and respiratory infections and, later on, to diagnose Pneumocystis carinii pneumonia in patients infected with human immunodeficiency virus. The method was largely improved by the induction of sputum with aerosol of hypertonic saline and was extended to become part of the assessment of airway inflammation in bronchial asthma and chronic obstructive pulmonary disease. It was recently shown that induced sputum can be used to study interstitial lung diseases and, more specifically, sarcoidosis, non-granulomatous ILD, occupational lung diseases and other systemic diseases with lung involvement.