Is sputum induction useful for examining airway inflammation in asthma?  

Inducing patients to cough up a sample of sputum by having them inhale an aerosol, or mist, of saline (salt water) has been used to test for lung cancer, tuberculosis, and other infections for many years. The idea of using saline aerosol to induce people with asthma to cough up a sample of sputum, which could then be analyzed for the presence and activity of inflammatory cells, occurred to us and to investigators in Canada at about the same time. Our first step was to determine whether examining the cells and chemicals in the induced sputum samples from people with asthma would differ from the cells and chemicals in the induced sputum samples from people without asthma. Our next step was to study whether induced sputum samples would contain more inflammatory cells after allergen inhalation and fewer after treatment with prednisone or with an inhaled corticosteroid.

Our results fulfilled our expectations.  

Our first study of 10 volunteers without asthma and of 18 volunteers with asthma showed sputum induction with saline mist to be easy to do, safe, and well tolerated. The sputum from the asthmatics contained more of a certain type of inflammatory cell, the eosinophil, and more of the chemicals made by eosinophils and by mast cells. We also found more mucin, the major protein in bronchial mucus, in the sputum from the asthmatics. These differences resemble those that have been found in actual biopsies of the airways from asthmatic and healthy subjects.

Our studies of the effects of inhaling allergen and of taking anti-inflammatory medications also showed that induced sputum samples reflect changes in the airways. The samples after allergen challenge contained more eosinophils; the samples after steroid treatment showed the opposite.

We are proud of this work, for it has led to the development of a useful, well tolerated tool for research on the diagnosis and treatment of asthma that has been adapted by many asthma researchers around the world. Details about this work are in a series of articles in scientific journals. 

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Fahy JV, Wong H, Liu J, Boushey HA. Comparison of samples collected by sputum induction and bronchoscopy from asthmatic and healthy subjects. American Journal of Respiratory and Critical Care Medicine 1995;152:53-58.

Fahy JV, Liu J, Wong H, Boushey HA. Analysis of cellular and biochemical constituents of induced sputum after allergen challenge: A method for studying allergic airway inflammation. Journal of Allergy and Clinical Immunology 1994;93:1031-1039.

Claman D, Boushey HA, Liu J, Wong H, Fahy JV. Analysis of induced sputum to examine the effects of prednisone on airway inflammation. Journal of Allergy and Clinical Immunology 1994;94:861-869.

Fahy JV, Liu J, Wong H, Boushey HA. Cellular and biochemical analysis of induced sputum from asthmatic and healthy subjects. American Review and Respiratory Diseases 1993;147:1126-1131.

Fahy JV, Steiger DJ, Liu J, Basbaum CB, Finkbeiner WE, Boushey HA. Markers of mucus secretion and DNA levels in induced sputum from asthmatic and healthy subjects. American Review and Respiratory Diseases 1993;147:1132-1137

Last Update: 5/24/06