title: What is severe asthma?
abstract: Asthma is common, and some individuals are severely affected by it. Learned institutions have sought to provide a definition of 'severe asthma' to facilitate research and clinical care. This is a challenging undertaking given the difficulty in defining asthma and the lack of supportive evidence for a distinct severe asthma phenotype. In this review, we discuss the rationale for a definition of severe asthma and the relative merits of the sequential attempts that have been made to produce such a definition. The difficulty in disentangling control and severity is highlighted, as is the heterogeneity of phenotype in severe asthma, and potential for misclassification. We conclude that the search for a singular definition of severe asthma is problematic, though likely to continue. We suggest the alternative strategy of using classifiers with a specific aim related to symptoms, pathophysiology or service provision.
authors.affiliation: Department of Respiratory Medicine, University of Nottingham, Nottingham, UK. john.blakey@nottingham.ac.uk
authors.forename: J D
authors.initials: JD
authors.lastname: Blakey
authors.forename: A J
authors.initials: AJ
authors.lastname: Wardlaw
mesh_terms: D001249:Asthma / Q000145:classification / Q000175:diagnosis*; D018450:Disease Progression; D006801:Humans; D012720:Severity of Illness Index