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The development of standardized methods for sputum induction has improved the quality and reproducibility of sputum samples. This technique has been used to optimize samples in the investigation of pulmonary tuberculosis and lung cancer, but its clinical application as a noninvasive measure of airway inflammation has highlighted the enormous potential of this technique. Sputum induction has allowed researchers to characterize the inflammatory profiles of a variety of airway diseases including asthma, COPD, and chronic cough. To date, the identification of sputum eosinophilia has the greatest clinical value as this predicts a favorable response to corticosteroids and can therefore guide treatment. In asthma and COPD management, protocols aimed at normalizing the sputum eosinophil count have markedly reduced exacerbations without an overall increase in therapy. Currently, no other noninvasive measure of airway inflammation has demonstrated a benefit in reducing exacerbations. The value of sputum induction and analysis is not restricted to the recognition of sputum eosinophilia but also may be used to direct novel antineutrophilic therapies. Thus, it is time for sputum induction to move from the research laboratory to the clinic. (CHEST 2006; 129:1344-1348)
Key words: asthma; COPD; cough; sputum
Abbreviation: eNO = exhaled nitric oxide
Analysis of sputum in respiratory disease has a long pedigree. However, in many clinical settings induced-sputum analysis is hampered as an investigative tool by the inability to obtain an adequate sample. This problem has been overcome by inducing sputum using hypertonic saline solution.1 This technique has now been applied to a number of diverse conditions. The improved yield and quality of sputum samples afforded by sputum induction provides a real alternative to bronchoscopy and BAL in the diagnosis of pulmonary tuberculosis, and has rekindled interest in sputum cytology in the management of lung cancer. However, the development over the last 15 to 20 years of this technique as a noninvasive measure of airway inflammation has focused much attention on the potential clinical application of this technique in the assessment of airway disease.1
Airway disease accounts for a significant proportion of a respiratory specialist's caseload. The main airway diseases asthma and COPD are defined in terms of typical symptoms and abnormal airway physiology, but additionally it is well recognized that airway inflammation is a key component of both diseases. Although...