Sputum neutrophil differential cell count in health and relationship to disease severity in asthma

Barber, Clair, Elliott, Scott, Ward, Jon, Gove, Kerry, Brown, Tom, Rupani, Hitasha, Hinks, Timothy, Djukanovic, Ratko, Kurukulaaratchy, Ramesh, Chauhan, Anoop and Howarth, Peter (2014) Sputum neutrophil differential cell count in health and relationship to disease severity in asthma. European Respiratory Journal, 44 (Suppl 58), [1691].

Abstract

Rationale: Sputum inflammometry has been used to phenotype asthma, with eosinophilic, neutrophilic, mixed granulocytic and paucicellular sub-groups described. Both ≥40% and ≥61% have been used as criteria to define sputum neutrophilia. Methods: As part of the Wessex Severe Asthma Cohort study, induced sputum was obtained from healthy non-asthmatic controls (HC, n=67), non-steroid treated asthmatics (MA , n=44), steroid treated (step 2/3) asthmatics (ModA, n=44) and those with severe (step 4/5 treated)asthma (SA, n=246) and differential cell counts obtained. Sputum neutrophil counts were not normally distributed and group comparisons were undertaken using non-parametric statistical analysis. Results: Median [1QR] sputum neutrophil % was significantly greater (p<0.001) in the SA (51.0 [38.7] than either HC (19.3 [31.50], p<0.0001), MA (25.40 [31.37], p<0.0001) or ModA (31.05 [41.70], p=0.005). ModA neutrophil % was significantly higher than HC (p<0.02) but not MA. The respective proportion of subjects (%) with neutrophil % of ≥40% and ≥61% was: SA (65.4 and 39.4), ModA (43.2 and 22.7), MA (31.8 and 15.9), HC (25.4 and 12.9). In SA neutrophil% in sputum was independent of smoking history, atopic status or oral steroid use and very weakly correlated with age and FEV1% predicted (inverse) (each R2 = 0,031, p=0.005). Sputum eosinophilia (≥2%) was evident in 34.8% and 29.9% of those with≥40% and ≥61%sputum neutrophilia respectively. Conclusion: Neutrophilic asthma is a prominent phenotype in severe asthma with approximately one third also having co-existent airway eosinophilic inflammation independent of the definition. Funding: WSAC was funded by the Medical Research Council UK.

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Contributors

Author: Clair Barber

Author: Jon Ward

Author: Ratko Djukanovic

Author: Ramesh Kurukulaaratchy

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