Derivation and validation of a composite index of severity in chronic obstructive pulmonary disease: the DOSE Index.

Abstract

Chronic obstructive pulmonary disease (COPD) is increasingly recognized as a multicomponent disease with systemic consequences and effects on quality of life. Single measures such as lung function provide a limited reflection of how the disease affects patients. Composite measures have the potential to account for many of the facets of COPD. To derive and validate a multicomponent assessment tool of COPD severity that is applicable to all patients and health care settings. The index was derived using data from 375 patients with COPD in primary care. Regression analysis led to a model explaining 48% of the variance in health status as measured by the Clinical COPD Questionnaire with four components: dyspnea (D), airflow obstruction (O), smoking status (S), and exacerbation frequency (E). The DOSE Index was validated in cross-sectional and longitudinal samples in various health care settings in Holland, Japan, and the United Kingdom. The DOSE Index correlated with health status in all data sets. A high DOSE Index score (> or = 4) was associated with a greater risk of hospital admission (odds ratio, 8.3 [4.1-17]) or respiratory failure (odds ratio, 7.8 [3.4-18.3]). The index predicted exacerbations in the subsequent year (P < or = 0.014). The DOSE Index is a simple, valid tool for assessing the severity of COPD. The index is related to a range of clinically important outcomes such as health care consumption and predicts future events.