A number of studies have suggested a pathogenetic role for airway inflammation in the induction of both chronic sputum production and chronic airflow obstruction in smokers.1 It is therefore important to characterise and quantify inflammatory changes in the assessment of subjects with chronic obstructive pulmonary disease (COPD). Assessment of inflammation may be achieved by different means including invasive methods such as bronchial biopsies, bronchoalveolar lavage (BAL) or examination of surgical specimens and non-invasive methods such as spontaneous or induced sputum.

The induction of sputum by inhalation of hypertonic saline is a safe, reliable, and relatively non-invasive method in COPD, provided the technique is performed in a standardised way and measures are used to prevent adverse reactions.2-4 Induced sputum differs from spontaneous sputum by having a higher number of viable cells and less squamous cell contamination.3 There are no differences between spontaneous and induced samples from patients with COPD or asthma in the total and differential cell counts, but there is poor agreement in the fluid phase components.5 ,6

Bronchial biopsies and BAL can be performed in COPD for investigative use according to the published recommendations.7 ,8 When the different methods of assessing airway inflammation are compared in the same subjects, a different profile of inflammatory cells is obtained depending on the compartment of the lung examined by each technique—that is, the lumen of the central airways using sputum analysis,9 the airway wall using bronchial biopsies, and the peripheral airways using BAL.10 By combining these techniques, integrated and comprehensive information on cell traffic and inflammatory processes in COPD at different levels of the airway can be obtained. Analysis of induced or spontaneous sputum has contributed to the identification of smokers susceptible to developing COPD, to the characterisation of the inflammatory process during …