Definitions and commonly used terms
A working definition of asthma
Asthma is a chronic lung disease, which can be controlled but not cured.
In clinical practice, asthma is defined by the presence of both the following:
- excessive variation in lung function (‘variable airflow limitation’, i.e. variation in expiratory airflow that is greater than that seen in healthy people)
- respiratory symptoms (e.g. wheeze, shortness of breath, cough, chest tightness) that vary over time and may be present or absent at any point in time.
In young children in whom lung function testing is not feasible, including most preschool children, asthma is defined by the presence of variable respiratory symptoms.
Untreated asthma is usually characterised by chronic inflammation involving many cells and cellular elements,1 airway hyperresponsiveness,1 and intermittent airway narrowing (due to bronchoconstriction, congestion or oedema of bronchial mucosa, mucus, or a combination of these).
Asthma probably represents a spectrum of conditions with different pathophysiological mechanisms.2 In older patients, there may be substantial overlap with the features of COPD.
The diagnosis of allergic asthma is more likely when the person also has allergy and a family history of asthma.
To confirm the diagnosis of asthma, it is necessary to demonstrate excessive variation in lung function, i.e. variation in expiratory airflow that is greater than that seen in healthy people (variable airflow limitation) – e.g. by spirometry in adults and in children old enough to perform the test – but it is not necessary to demonstrate airway hyperresponsiveness in a laboratory test or to demonstrate the presence of inflammatory cells in the airway. Respiratory symptoms may be due to many conditions other than asthma, so:
- the diagnosis of asthma is based on the probability that symptoms and clinical findings are due to asthma
- to confirm the diagnosis, lung function testing must be done at a time when the person does not have a respiratory tract infection3
- the evidence for variable airflow limitation must be documented at the time of diagnosis
- in young children, especially pre-schoolers (who cannot perform spirometry), it can be difficult to diagnose asthma with certainty.
In this section
Definitions of special terms used the handbook, including descriptions of inhaled corticosteroid dose levels and specific aspects of asthma
Explanation of abbreviations used in the handbook, technical terms, and terms for which alternatives are commonly used
- Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention. GINA, 2012. Available from: http://www.ginasthma.org
- Anderson GP. Endotyping asthma: new insights into key pathogenic mechanisms in a complex, heterogeneous disease. Lancet. 2008; 372: 1107-19. Available from: http://www.ncbi.nlm.nih.gov/pubmed/18805339
- Melbye H, Kongerud J, Vorland L. Reversible airflow limitation in adults with respiratory infection. Eur Respir J. 1994; 7: 1239-1245. Available from: http://www.ncbi.nlm.nih.gov/pubmed/7925901