Induced Sputum in Asthma

The goals of asthma management are the accurate diagnosis and effective control of symptoms, including nocturnal symptoms and exercise induced asthma, prevention of exacerbations, and the achievement of best pulmonary function with minimal side effects (1). Whilst this is achieved in the majority of patients, there remains a significant number who are misdiagnosed (2) or who suffer from troublesome symptoms and frequent exacerbations (3). The routine diagnosis and treatment of asthma in primary-care and most secondary care settings involves evaluating variable airflow obstruction with spirometry and peak flow measurement, and assessing symptom control, but does not normally assess the two cardinal features of asthma: airway inflammation and airway hyper-responsiveness. The question arises as to whether extending the goal of management to include these features may lead to better outcomes. Current treatment guidelines for asthma involve a concept of a stepwise increase in medication based on symptom control and peak flow measurements (1). However, patients who appear clinically well controlled on inhaled corticosteroids can still have evidence of airway inflammation and airway hyper-responsiveness (4,5) and be vulnerable to exacerbations, airway remodeling and possibly fixed airways obstruction (6,7). A treatment strategy based on an attempt to return airway responsiveness towards normal has been shown to reduce exacerbations and reduce sub-epithelial reticular basement thickening (8). The development of feasible and valid non-invasive methods to assess air- way inflammation has made it possible to examine whether assessment of airway inflammation improves outcomes in patients with asthma. Assessment of airway inflammation may lead to more accurate diagnosis as well as better identification of vulnerable patients who need more intensive anti-inflammatory treatment. However, in order to be useful, the method used to assess airway inflammation needs to be feasible in a clinical setting and the results need to inform the physician about clinically important aspects of the disease that cannot be discerned by a simpler method. In this chapter, we discuss to what extent assessment of airway inflammation using induced sputum fulfills these criteria.