Related Experiment Video
Updated: Jun 19, 2026
Methodology for Sputum Induction and Laboratory Processing
Published on: December 17, 2017
Assessment and reproducibility of non-eosinophilic asthma using induced sputum
Jodie L Simpson1, Patrick McElduff, Peter G Gibson
1Centre for Asthma and Respiratory Disease, The University of Newcastle, Callaghan, NSW, Australia. Jodie.simpson@hnehealth.nsw.gov.au
Background:
The assessment of eosinophilic airway inflammation using induced sputum identifies a corticosteroid-responsive subtype that can be used to guide anti-inflammatory therapy. The stability of airway inflammation in asthma over time is not known, yet this information is crucial to inflammation-based patient management.
Objective:
The aim of this study was to determine the reproducibility of non-eosinophilic asthma.
Methods:
Participants with stable asthma (n = 26) underwent a sputum induction each month for 5 months. Sputum was dispersed and differential cell counts were performed. The reproducibility of inflammatory subtype with different eosinophil cut points (starting at 1% eosinophils) was examined and the minimum number of visits required to determine inflammatory subtype was calculated.
Results:
One hundred and twenty- two sputum samples were obtained (success 94%). All cut points greater than 2% eosinophils were reproducible and a 3% cut point resulted in the highest agreement with a kappa statistic of 0.538. Specificity and sensitivity were high for determining inflammatory subtype after 1 or 3 sputum samples.
Conclusions:
A cut point of 3% eosinophils should be used to distinguish eosinophilic from non-eosinophilic airway inflammation in asthma. This allows a single sputum sample to be used to reliably determine the presence of eosinophilia.
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