Assessment and reproducibility of non-eosinophilic asthma using induced sputum

Respiration. 2010;79(2):147-51. doi: 10.1159/000245899. Epub 2009 Oct 8.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Asthma / immunology*
  • Eosinophilia / diagnosis*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Reproducibility of Results
  • Sample Size
  • Sputum / cytology*