Asthma phenotypes: Consistency of classification using induced sputum

• Published in: Respirology (Carlton, Vic.) Vol. 17; no. 3; pp. 461 - 466
• Main Authors: HANCOX, ROBERT J., COWAN, DOUGLAS C., ALDRIDGE, RUTH E., COWAN, JAN O., PALMAY, ROCHELLE, WILLIAMSON, AVIS, TOWN, G. IAN, TAYLOR, D. ROBIN
• Format: Journal Article
• Language: English
• Published: Melbourne, Australia Blackwell Publishing Asia 01.04.2012
• Subjects: Adult; Anti-Asthmatic Agents - therapeutic use; Asthma - classification; Asthma - drug therapy; Asthma - pathology; Budesonide - therapeutic use; eosinophil; Eosinophilia - classification; Eosinophilia - pathology; Eosinophils - pathology; Female; Humans; Leukocyte Count - classification; Male; Middle Aged; neutrophil; non-eosinophilic asthma; Sputum - cytology; Terbutaline - therapeutic use; Young Adult
• ISSN: 1323-7799; 1440-1843; 1440-1843
• DOI: 10.1111/j.1440-1843.2011.02113.x

ABSTRACT Background and objective:  Asthma can be classified as eosinophilic or non‐eosinophilic based on the cell profile of induced sputum. This classification can help determine whether corticosteroid treatment is indicated. We assessed the stability of these phenotypes over time and with different treatment regimens. Methods:  Clinically stable, non‐smoking, asthmatic adults were enrolled in one of two studies. In study one, induced sputum cell counts from 28 subjects were analysed after 4 weeks without corticosteroid treatment and after 6 week treatments with placebo, regular inhaled beta‐agonist, inhaled corticosteroid, and combined beta‐agonist and corticosteroid. In study two, sputum from 26 subjects with non‐eosinophilic asthma was analysed after 12 weeks of placebo and after four 2‐week corticosteroid washouts. Sputum with <2% eosinophils was classified as non‐eosinophilic. Results:  Sputum classification changed frequently in both studies. In study one, only one of eight participants with non‐eosinophilic sputum after placebo treatment remained non‐eosinophilic throughout. In study two, all of participants had at least one eosinophilic sputum sample, despite the fact that all had been non‐eosinophilic at recruitment. Neutrophilic asthma was uncommon in both studies and was also inconsistent. Conclusions:  The phenotypic classification of asthma changes frequently. A diagnosis of non‐eosinophilic asthma should not be based on a single sputum sample. The stability of the classification of asthma phenotypes was studied in two clinical trials. Participants' sputum frequently changed between eosinophilic and non‐eosinophilic inflammation. These changes occurred both spontaneously and in response to treatment. A diagnosis of non‐eosinophilic‐asthma should not be based on a single sputum sample.