Definitions of severity and outcome measures

Outcome measurement is still a difficult area in general, and in asthma in particular, with further research needed. (Attributable) outcomes of health care are the only sort of outcome measure which are of direct use as a contracting tool. However, less well-researched and understood outcomes are useful as quality improvement tools, and within more open-ended discussions involving purchasers and providers. In terms of hospital care of acute asthma, there is no well-defined outcome measure which reflects the quality of hospital care; re-admission rates show promise as an outcome measure which relate to the quality of discharge planning and merit further study. In terms of ambulatory care, there is an urgent need to develop and evaluate a symptom-based outcome measure which would be usable in routine practice and could be recommended for widespread use. As a physiological outcome measure, percentage of best function is one which corrects for the degree of irreversible air flow obstruction and is independent of treatment step. It is valuable for individual patients by providing a realistic gold standard and if best function is assessed in a standard manner, it also allows results of groups of patients to be compared in a meaningful manner. Severity scores, which might allow categorization of patients on the basis of characteristics other than current symptoms or therapy, are currently being evaluated.