The Article in Brief

Defining Comorbidity: Implications for Understanding Health and Health Services

Jose M. Valderas , and colleagues

Background Even though clinicians often treat patients with multiple medical conditions (comorbidity), there is no agreement about how to define and measure comorbidity. This article reviews concepts and definitions related to comorbidity from the perspective of health care professionals.

What This Study Found There are several definitions of comorbidity. Although always applied to the individual patient, these definitions distinguish between the nature and relative importance of the health conditions, the order in which the conditions present themselves, and expanded conceptualizations. There are 3 main research areas that use and measure these concepts: (1) clinical care, (2) epidemiology and public health, and (3) health service planning and financing. Each area needs to apply different concepts of comorbidity for its purposes. The article also explores mechanisms that may underlie comorbid conditions in a patient.

Implications

• Use of explicit definitions and concepts, along with established disease classifications, would make research findings more precise and generalizable, and could increase understanding of the causes and consequences of co-occurring diseases.
• More research is needed into patients' perspectives on the ways in which multiple conditions affect their health, well-being, and clinical care.