Impact of 'mild' asthma on health outcomes: findings of a systematic search of the literature.

The present bibliographic review shows that patients considered to have mild asthma often suffer impairment in quality of life (QoL) and use considerable scheduled and unscheduled health care resources. I found that asthma investigators used no consistent classification scheme for asthma severity, and the level of agreement amongst specialists when categorizing patients with asthma was low. Asthma severity has been classified using a wide range of parameters including medication use, asthma symptoms, lung function, hospitalizations and incidence of exacerbations. Most studies showed a general association between asthma severity and health-related quality of life (HRQoL) such that patients with severe disease suffered greater impairment. However, few patients with mild asthma enjoyed unimpaired HRQoL. Indeed depression and impaired HRQoL were reported as frequently in patients with mild asthma as in those with more severe disease. Although in general severe patients used the most health care resources, even patients with mild asthma used considerable health care resources including emergency room care and hospitalizations. In summary, the term 'mild' when applied to asthma is potentially misleading given the impaired HRQoL and avoidable health care utilization prevalent amongst such patients. The application of disease severity classification in clinical asthma management has not been validated. It may now be appropriate to examine these classifications more critically in order to determine if they have clinical or research usefulness. By contrast, the strategy of treating to achieve disease control has been validated and offers the advantage of simplicity in its application.