Sputum eosinophils and asthma control in daily practice

Published online: April 4, 2017

The technique of induced sputum is a well-recognized noninvasive technique to assess airway inflammation in patients with asthma. Sputum is induced by inhalation of saline for 10-20 minutes with an ultrasonic nebulizer, collected and then processed with a mucolytic agent before performing a differential cell count. The presence of eosinophils in sputum is a cardinal feature of asthma and has been shown to be associated with the disease severity and in particular with the propensity to develop exacerbations. Inhaled corticosteroids are able to reduce sputum eosinophils and asthma exacerbations. Contrary to the relationship between sputum eosinophilia and the risk of exacerbations, the relationship between sputum eosinophils and day-to-day asthma control is still controversial in the literature.

In a recent article published in The Journal of Allergy and Clinical Immunology: In Practice, Demarche and colleagues assessed the relationship in daily practice between the fluctuations in sputum eosinophils over time and asthma control, defined by the “Asthma Control Questionnaire-6 items” score. The authors retrospectively collected data from an initial cohort of 187 patients who had produced at least 2 readable sputum samples as part of routine investigation in an Asthma Clinic of a University Center. A second independent cohort of 79 patients was also analyzed in order to validate the results of the initial cohort.

After multiple regression analysis, the authors found that asthma control was associated with individual changes in sputum eosinophils over time, with an increase in sputum eosinophils being associated with a worsening of asthma control, and a decrease in sputum eosinophils with an improvement in asthma control. This finding was confirmed in the validation cohort. The results of this article also suggested that inhaled corticosteroids provide asthma control by modulating eosinophilic inflammation.

This study therefore encourages the clinician to monitor sputum eosinophilic inflammation in order to reduce it as much as possible. The data suggest that patients with uncontrolled eosinophilic asthma despite usage of corticosteroids have room for improvement in asthma control by intensifying treatment with inhaled corticosteroids. Conversely, in patients with noneosinophilic asthma, it is unlikely that an increase in the dose of inhaled corticosteroids will improve asthma control.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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