Sputum colour can identify patients with neutrophilic inflammation in asthma

Kavita Pabreja; Peter Gibson; Alyssa J Lochrin; Lisa Wood; Katherine J Baines; Jodie L Simpson

doi:10.1136/bmjresp-2017-000236

Sputum colour can identify patients with neutrophilic inflammation in asthma

BMJ Open Respir Res. 2017 Oct 9;4(1):e000236. doi: 10.1136/bmjresp-2017-000236. eCollection 2017.

Authors

Kavita Pabreja¹, Peter Gibson¹, Alyssa J Lochrin², Lisa Wood², Katherine J Baines², Jodie L Simpson²

Affiliations

¹ Priority Research Centre for Healthy Lungs, School of Medicine and Public Health, Hunter Medical Research Institute, The University of Newcastle, Newcastle, New South Wales, Australia.
² Priority Research Centre for Healthy Lungs, School of Biomedical Sciences and Pharmacy, Hunter Medical Research Institute, The University of Newcastle, Newcastle, New South Wales, Australia.

Abstract

Introduction: Sputum colour is associated with neutrophilic inflammation in chronic bronchitis and chronic obstructive pulmonary disease (COPD). Neutrophilia and sputum expectoration is notable in asthma, but whether sputum colour is associated with and predicts the presence of neutrophilic inflammation in asthma is unknown. The objective of the study is to assess the ability of sputum colour in distinguishing asthma inflammatory phenotypes.

Methods: Induced sputum samples collected from 271 adults with stable asthma were retrospectively assessed. Sputum colour was determined using the BronkoTest sputum colour chart and correlated to differential cell counts and CXCL-8 concentration. Neutrophilic inflammation was defined as an age-corrected sputum neutrophil proportion (≥61.6% for age 20-40 years; ≥63.2% for age 40-60 and ≥67.2% for age >60 years), whereas neutrophilic bronchitis (NB) was defined as high total cell count (≥5.1×10⁶ cells/mL) plus an increased age-corrected neutrophil proportion. The optimal cut-off for sputum colour to predict neutrophilic inflammation and NB was determined using receiver operator characteristic curve analysis.

Results: A sputum colour score of ≥3 represented and predicted neutrophilic inflammation with modest accuracy (area under the curve (AUC)=0.64; p<0.001, specificity=78.4%, sensitivity=49.2%). Participants with a sputum colour score of ≥3 had significantly (p<0.05) higher CXCL-8, total cells and neutrophil number and proportion. Sputum colour score was also positively correlated with these factors. Sputum colour score ≥3 predicted NB with reasonably good accuracy (AUC=0.79, p<0.001, specificity=79.3%, sensitivity=70.7%).

Conclusions: Visual gradation of sputum colour in asthma relates to high total cell count and neutrophilic inflammation. Assessment of sputum colour can identify adults with asthma who are likely to have NB without the need for sputum processing and differential cell count, which may facilitate asthma management.

Keywords: asthma; inflammation; neutrophilic bronchitis; neutrophilic inflammation; neutrophils; sputum; sputum colour.