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Sputum induction as a method of analyzing pulmonary cells: reproducibility and acceptability
P S Thomas1, D H Yates, P J Barnes
1Department of Thoracic Medicine, National Heart and Lung Institute, London, UK. paul.thomas@unsw.edu.au
Summary
Sputum induction is safe and acceptable for assessing airway inflammation in asthma patients and healthy individuals. While it caused a slight decrease in lung function in healthy subjects, this was prevented in asthmatics with medication, showing good reproducibility for total cell counts.
Area of Science:
- Pulmonary Medicine
- Respiratory Cell Biology
- Clinical Immunology
Background:
- Sputum induction is a noninvasive method for sampling airway cells to assess airway inflammation in asthma.
- Its clinical applicability for managing anti-inflammatory therapy in a respiratory clinic setting remains unevaluated.
- Research settings have demonstrated its utility, but clinical translation requires assessment of patient factors and technique reliability.
Purpose of the Study:
- To evaluate the clinical applicability of sputum induction in an asthma clinic setting.
- To assess patient acceptability, effects on airway caliber, and reproducibility of cell counts at 2-week intervals.
- To compare these parameters between asthma patients and normal controls.
Main Methods:
- Thirty-seven subjects (20 asthmatics, 17 normal controls) underwent standardized sputum induction using inhaled 3.5% saline over 12 minutes on two occasions, 2 weeks apart.
- Patient acceptability was assessed via questionnaire; airway caliber was measured by spirometry, with asthmatics receiving albuterol premedication.
- Total and differential cell counts of induced sputum were analyzed and correlated with bronchial hyperresponsiveness and technique reproducibility.
Main Results:
- Sputum induction was found to be safe and acceptable for all subjects, with mild side effects reported by over 90%.
- A significant decrease in forced expiratory volume in 1 second (FEV1) was observed in normal subjects, but not in asthmatics pre-medicated with albuterol.
- Reproducibility of total pulmonary cell yield at 2 weeks showed a reliability coefficient of 0.77, though variability existed in differential cell counts.
Conclusions:
- Sputum induction is a safe and well-tolerated procedure for both asthmatic and normal individuals in a clinical setting.
- Albuterol premedication effectively prevents the decrease in FEV1 observed in normal subjects, making the technique suitable for asthmatics.
- While total cell counts are reproducible, variability in inflammatory cell counts may limit its value in a clinical setting compared to research.