Repeatability of induced sputum measurements in moderate to severe asthma

Matthew Richard William Rossall, Paul Aidan Cadden, Stephanie Dawn Molphy, Jonathan Plumb, Dave Singh

    Research output: Contribution to journalArticlepeer-review


    Background: Novel therapies are being developed for patients with moderate to severe asthma. These patients may have neutrophilic airway inflammation. Induced sputum is commonly used as an endpoint in clinical trials of asthma therapies. We have performed repeated induced sputum sampling in moderate to severe asthma patients to understand the variability of cell counts, including neutrophils, and performed power calculations for studies in this group of patients. Methods: Nineteen patients with moderate to severe asthma with evidence of airflow obstruction (FEV1 ≤ 80% predicted) and suboptimal control (ACQ ≥ 1) performed repeated induced sputum separated by 1 month. Results: The Ri of neutrophil percentage and absolute eosinophil count demonstrated good (0.61) and moderate (0.56) repeatability respectively, but there was a poor level of agreement for eosinophil percentage and absolute neutrophil counts. The within subject SD for sputum neutrophil percentage was 15.8. In cross over studies, sample sizes of n = 14 and n = 54 are required to detect changes in neutrophil percentages by 20 and 10 % respectively at 90% power. Conclusions: Sputum neutrophil percentage has good reproducibility in patients with moderate to severe asthma. © 2014 Elsevier Ltd.
    Original languageEnglish
    JournalRespiratory Medicine
    Publication statusPublished - 21 May 2014


    • Induced sputum
    • Neutrophils
    • Repeatability
    • Severe asthma


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