Background: The World Health Organization's International Classification of Functioning, Disability and Health (ICF) has provided a new foundation for our understanding of health, functioning, and disability. As a content-valid, comprehensive and universally applicable health classification, it serves as a platform to clarify and specify health-related concepts that are frequently used in the medical literature. The health concepts to which we refer are: well-being, health status, quality of life (QoL) and health-related quality of life (HRQoL).
Objective: The aim of this paper is to use the ICF as a conceptual platform to specify and discuss health-related concepts.
Methods: The ICF entities health and health-related domains and functioning will be used as starting point to reach the objective of the paper. Health domains refer to domains intrinsic to the person as a physiological and psychological entity, such as mental functions, seeing functions, and mobility. Health-related domains are not part of a person's health but are so closely related that a description of a person's lived experience of health would be incomplete without them. Examples of health-related domains are work, education, and social activities. Functioning refers to all health and health-related domains within the ICF.
Results: Well-being is made up of health, health-related, and non-health-related domains, such as autonomy and integrity. Health state is a health profile that results from collecting together health domains. Functioning states is a profile that results from collecting both health and health-related domains. Health status is a summary measure of health state. Functioning status is a summary measure of functioning state. QoL is the individual's perceptions of how the life is going in health, health-related, and non-health domains. HRQoL is the individual's perceptions of how the life is going in health and health-related domains.
Discussion: "HRQoL is to QoL as functioning is to well-being". The ICF represents a standardized and international basis for the operationalization of health based on its health domains. It refers to the more restricted concepts of health state and health status. The ICF is also the basis for the operationalization of functioning based on all health and health-related domains contained therein. The authors argue that functioning is an operationalization of health from a broader perspective. It refers to an operational concept of health in terms of a set of health domains ('under the skin') and health-related domains ('outside the skin') that consider the individual person not only as a biological but also as a social entity. Health from this perspective refers to the broader notion of functioning state and functioning status. Nevertheless, the ICF provides more than a basis for the operationalization of health and functioning. The ICF also contains contextual factors.