The international classification for functioning, disability and health
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- Boonen, A., Rasker, J.J. & Stucki, G. Clin Rheumatol (2007) 26: 1803. doi:10.1007/s10067-007-0623-0
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Health information is the glue that holds a health system together. In most countries stronger, more integrated information systems are required .
The rheumatologic community is in a leading position for the development of International Classification of Functioning, Disability and Health (ICF) Core Sets and the research into the validity and application of the ICF. We can be proud of this achievement, but not all of us are aware of this new development. What is the ICF?
Rheumatologic conditions have major impact on patients. Apart from symptoms such as pain, stiffness, and fatigue, patients are limited in activities and restricted in participation in society . When unable to continue paid work, for example, there are important consequences for the patients, their families, but also for society. A major goal of the management of rheumatic diseases is to maintain or restore functioning. This contributes to the well-being of the patients, their families, and other caregivers. It is clear that maintaining function requires more than control of disease activity. By using the ICF, which was developed by the World Health Organization (WHO), we can obtain information on all three areas that are important for global functioning: body functions and structures, activities (actions by an individual), and participation (involvement in life situations) .
The ICF is one of the three reference classification systems that were proposed and developed by the WHO and belong to the Family of International Classifications. The main aim of the classification systems is to improve integration of health information. The International Classification of Diagnosis (ICD) is well known and widely applied . The ICF was developed from the older International Classification of Impairments, Disabilities, and Handicaps (ICIDH) and accepted in 2001 . It is increasingly recognized as an important classification in clinical medicine, outcome research, and healthcare organization. The International Classification of Health Interventions (ICHI) is proposed as the newest member of the family, and its development has just started .
The WHO aims to implement effectively the ICF worldwide and formulated strategic directions in which the three following are the most relevant: (1) The ICF has to become the framework to classify function, (2) easy-to-use ICF linked instruments should be developed to assess functional outcome as well as effectiveness of interventions, and (3) the level and quality of implementation of the ICF should be improved to increase quality and comparability of health and disability statistics for national and international purposes .
In this review, the ICF framework and classification are explained from the broader perspective of the history of outcome assessment. Healthcare areas in which the ICF can be useful will be addressed. Finally, the strengths of the ICF will be challenged by the research agenda.
The ICF as the universal framework for functioning: a historical view
Why is the ICF called “the universal” classification for functioning?
The ICF Core Sets
To apply the ICF in practice, either in patients with a specific condition (like RA) or in specific healthcare situations (like acute or post-acute care), ICF Core Sets are being developed. These comprise specific categories relevant for a particular condition or a specific situation .
At present, first versions of ICF Core Sets have been published for 12 chronic health conditions among which 5 are for musculoskeletal diseases: RA, osteoporosis, osteoarthritis, low back pain, and chronic widespread pain [20–24]. The first versions of these ICF Core Sets are currently undergoing a worldwide testing and validation, including a cooperation project with EULAR for the five musculoskeletal ICF Core Sets. Additional ICF Core Sets for musculoskeletal disease are currently also being developed for psoriatic arthritis, ankylosing spondylitis, scleroderma, lupus, and gout [25, 26]. For the acute hospital and early post-acute rehabilitation facilities, ICF Core Sets have been developed for musculoskeletal, cardiovascular, and neurological conditions . Arthritis-specific ICF Core Sets have been developed for the acute and early post-acute situation [28, 29].
Upon completion and experience with the development of these ICF Core Sets, a Generic ICF Core Set is being developed that aims to include categories necessary to represent the experience of human functioning irrespective of the underlying health condition.
When developing the ICF Core Sets, a standardized approach is applied in which the perspective of patients, different types of health care providers, and outcome researchers are taken into account . As the categories of the specific ICF Core Sets originate from the universal ICF, the classifications can be easily understood across professionals and across conditions. The common definition of the categories and the standardized development of the Core Sets explains why the ICF is called a universal classification.
How to measure the ICF categories
It is specifically mentioned in the WHO business report that it is by no means the aim of the ICF to replace validated existing instruments. In contrast, it is likely that they will have an essential role to measure particular parts of the ICF.
The ICF classification provides for each category an optional scoring, the so-called ICF qualifiers. Qualifiers are numeric codes that specify the extent or the magnitude of the functioning or disability in that category or the extent to which an environmental factor is a facilitator or barrier. Such a qualifier may be directly be applied or can serve as reference scale if specific measures are being used. According to the ICF qualifier, the level of impairments in body functions and body structures or limitations or restrictions in activities and participation can be indicated on a 0 (no) to 4 (complete) scale. A “c” indicates the category is impaired or limited as a consequence of comorbidity, “8” that the level of impairment cannot be specified, and “9” that the category is not applicable. For the environmental factors, patients can specify the category is a barrier (−) or a facilitator (+) . The qualifiers can be directly applied to the categories or can serve as reference scale if specific measures are being used to qualify the categories.
Applications of the ICF Core Sets
The main stakeholders of the ICF are clinicians, researchers, and decision makers on the governmental level and, last but not least, governments. Most certainly, also patient organizations, healthcare organizations (health insurance companies, home care organizations, social security services), and media systems can benefit from the ICF .
As the ICF can classify functioning at the group but also at the individual level, it can be used in clinical practice. Especially in rehabilitation medicine, the comprehensive approach contributes to the planning of tailor made care for patients within the framework of the bio-psychosocial model. The assessment for vocational rehabilitation of a patient with RA, for example, requires careful evaluation of impairments in body functions (such as pain, energy level, sleep) and body structures (such as damage to the hand joints), limitations in activities (fine hand use, walking) and participation (using transportation services, self-care), but also identification of relevant environmental factors (medication, adaptations, attitudes of colleagues, attitudes of family members) and personal factors (age, marital state, educational level, coping strategies, illness perceptions) . Identification of the individualized relevant categories will make it possible to set priorities for treatment and to identify the health professionals responsible to execute each of the identified priorities . While the contribution of allied health professionals is recognized, the ICF will help defining the specific role and responsibilities of each professional for the different categories . The common ICF framework and language will improve not only communication among the different healthcare providers but also communication with the patients and nonmedical environment such as family and employers.
For researchers with an interest in outcome assessment, the ICF offers challenging opportunities. ICF Core Sets are useful for the design, the evaluation, and the reporting of studies examining the longitudinal course of disease or the efficacy and effectiveness of interventions. In the study design, ICF-based comparisons of candidate measures will help to select aspects of functioning, which most appropriately cover the patients’ problems that should be improved. Researchers have to pinpoint the targets and explanatory variables. Currently, we often lack an understanding of the mechanism that leads to progression of disease or improvement based on an intervention. The ICF offers an opportunity that not only enables to report about statistical and clinically relevant differences but also to demonstrate the mechanism of changes (over time or during interventions) on the level of functioning. Such analyses are only possible if at least a minimum set of variables covering all aspects relevant to people with the condition are covered. In addition, the ICF-based approach to follow cohorts or intervention studies will enable comparison of studies not only in people with the same condition but also across diseases when considering the Generic ICF Core Set in the study design.
From the perspective of the governments and healthcare organizations, there is a great interest in the ICF. For the WHO, it has a priority to demonstrate the utility and feasibility of using ICF in areas of strategic importance such as health and disability reporting, outcome measurement for clinical and epidemiological use, and disability assessment and certification by 2008. ICF-based data sets including ICF population norms and disability prevalence rates should be available by 2010. Healthcare organizations explore the application of the ICF for disability assessments, eligibility of technical aids and home care, and organization of social services. Such data will contribute to insight in planning of social security systems and home care, eligibility assessment for disability pensions, and technical aids.
While it is obvious that the ICF has made tremendous steps forward since its conception, it is clear at the same time that there is still a challenging way to go.
The first priority is to develop a classification for personal factors and the development of the Generic Core Set. As for any instrument, the classification has to prove it can pass the validity filter, especially with regard to discrimination and feasibility. From limited research, it is suggested that the reliability can be improved, probably because the ICF language is difficult to understand and because the qualifiers show differential functioning . This is especially true for many categories referring to participation and for most environmental factors that were relevant in all Core Sets and for which no other but ICF-based classifications exist. While there are many studies that address work participation, few validated instruments exist to assess absenteeism [36–39]. Even fewer instruments are developed to assess participation in nonwork-related social activities, except some items of generic instruments such as short-form (SF) 36  and of the Arthritis Impact Measurement Scales-2 (AIMS2) .
To improve feasibility, expanding the efforts to increase understanding and application of the ICF among a wider audience are still necessary. On this line, the exact approach on how existing measures can be integrated into the ICF classification needs further clarification and consensus. This will include the exploration of statistical methods to handle hierarchical data and complex relationship between the categories belonging to the components.
The adoption of the ICF in 2001 as a framework and classification was the recognition of the importance of the bio-psychosocial perspective to account for the human experience of functioning. Being a universal language, the ICF will improve our insight into the complexity of human functioning, help tailor-made care for the individual patient, and improve design and reporting of observational and interventional studies. The rheumatologic community has to be merited to be in a leading position for the development of Core Sets and the research into validity and application of the ICF. This illustrates again how, for the rheumatologist, the patient needs to be the starting as well as endpoint of his devotion.