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Derivation and Validation of a Composite Index of Severity in Chronic Obstructive Pulmonary Disease

The DOSE Index

¹ Respiratory Research Unit, Peninsula Medical School, University of Plymouth, Devon, and ² Department of Medicine, Academic Unit of Respiratory Medicine, University College London, London, United Kingdom; ³ Department of Public Health and Primary Care, Leiden University Medical Center, Leiden, The Netherlands; ⁴ Department of Pulmonary Medicine, Infection, and Oncology, Respiratory Care Clinic, Nippon Medical School, Tokyo, Japan; ⁵ Department of General Practice and Primary Care, Foresterhill Health Centre, University of Aberdeen, and ⁶ School of Psychology, University of Plymouth, Devon, United Kingdom

Correspondence and requests for reprints should be addressed to Rupert C. Jones, M.D., Respiratory Research Unit, Peninsula Medical School,1 Davy Road, Plymouth PL6 8BX, UK. E-mail: rupert.jones{at}pms.ac.uk

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.

Key Words: health status • outcome assessment • composite outcomes • disease severity

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Chronic obstructive pulmonary disease (COPD) is a complex disease, but current guideline recommendations for assessment of severity are based on airflow obstruction. Multicomponent indices have been developed but are not widely used in clinical practice. What This Study Adds to the Field The DOSE Index (MRC Dyspnea Scale, airflow obstruction, smoking status, and exacerbation frequency) was derived and validated in international data sets. Unlike other severity indices, this index is intended for use in routine clinical settings, not just as a measure of disease severity but also as a quick guide to management.