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Updated: Mar 20, 2026
Methodology for Sputum Induction and Laboratory Processing
Published on: December 17, 2017
Exacerbation risk in severe asthma is stratified by inflammatory phenotype using longitudinal measures of sputum
C J Walsh1, T Zaihra2, A Benedetti3,4,5
1Department of Medicine, Institute of Medical Sciences, Keenan Centre for Biomedical Research, Li Ka Shing Knowledge institute, St. Michael's Hospital, University of Toronto, Toronto, ON, Canada.
Background:
Airway inflammatory phenotyping is increasingly applied to subjects with asthma. However, its relationship to clinical outcomes in difficult asthma is incompletely elucidated.
Objective:
The goal of our study was to determine the relationship between exacerbation rates and phenotypes of difficult asthma based on the longitudinal measures of sputum eosinophils and neutrophils.
Methods:
Subjects in the longitudinal observational study from two tertiary care centres that completed 1 year of observation and provided at least three sputum samples were classified by inflammatory phenotypes using previously established thresholds. Kaplan-Meier curves and univariable and multivariable Cox proportional hazard models were used to determine the association between inflammatory phenotypes and exacerbation rate.
Results:
During the study, 115 exacerbations occurred in 73 severe asthmatic subjects. Subjects with the persistently eosinophilic phenotype had a significantly shorter time to first exacerbation and greater risk of exacerbation over a 1-year period than those with the non-eosinophilic phenotype based on the univariable and multivariable Cox proportional hazard model (hazard ratio [HR], 3.24; 95% confidence interval [CI], 1.35-7.72; adjusted HR, 3.90; 95% CI, 1.34-11.36). No significant differences in time to first exacerbation or exacerbation risk over a 1-year period were observed among the neutrophilic phenotypes.
Conclusions:
The persistent eosinophilic phenotype is associated with increased exacerbation risk compared with the non-eosinophilic phenotype in severe asthma. No differences in time to first exacerbation or exacerbation risk over a 1-year period were detected among neutrophilic phenotypes.
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