Derivation and Validation of a composite index of severity in chronic obstructive pulmonary disease

Rationale: 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. Objectives: To derive and validate a multicomponent assessment tool of COPD severity that is applicable to all patients and health care settings. Methods: 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. Measurements and Main Results: The DOSE Index correlated with health status in all data sets. A high DOSE Index score (≥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 ≤ 0.014). Conclusions: 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.