Based on (1) a systematic search of the literature on definitions of chronic conditions in childhood and (2) a theoretical framework of determinants and indicators of the health status of a population, which is described below, we proposed a definition of chronic conditions in childhood. This proposal was sent to experts and was subsequently adapted to their comments (3). The final definition was operationalised using the ICD-10 classification .
The first step in the consensus procedure was the performance of a systematic literature review. Details of this systematic review are described elsewhere . A wide range of definitions were in use, of which, four were cited by many other authors [15, 18, 20, 26]. Pless and Douglas proposed a definition for children with any chronic physical disorder for use in epidemiological surveys . They described chronic illness as “a physical, usually non-fatal condition which lasted longer than 3 months in a given year, or necessitated a period of continuous hospitalisation of more than one month; of sufficient severity to interfere with the child’s ordinary activities in some degree.” Perrin et al. presented some recommendations for formulating a comprehensive, generic and flexible definition of chronic conditions in childhood . They recommended two levels: duration and impact. First, “a condition is considered chronic if it has lasted or is expected to last more than 3 months.” And a second specification is “to take into account the impact of the condition on the child. For example, the level of functional impairment or the use of medical attention greater than that expected for a child of the same age might be considered.” Stein et al. defined “children with ongoing health conditions” as children having disorders that: (1) have a biological, psychological or cognitive basis; (2) have lasted or are virtually certain to last for at least 1 year and (3) produce one or more sequelae, such as: (a) limitations of function, activities or social role in comparison with healthy peers in the general areas of physical, cognitive, emotional and social growth and development; (b) dependency of medication, special diet, medical technology, assertive devices or personal assistance to compensate for or minimise the limitations of function, activities or social role or (c) the need for medical care or related services, psychological services or educational services over and above the usual for the child’s age, or for special ongoing treatments, interventions or accommodation at home or in school . McPherson et al. defined a slightly different concept, namely “children with special health care needs” . They described these children as “those who have or are at increased risk for a chronic physical, developmental, behavioural, or emotional condition and who also require health and related services of a type or amount beyond that required by children generally.” Apart from these four often cited definitions, several different definitions were found, some of which were based on a list of diagnoses and others were based on the duration and consequences of the condition of the child, the so-called non-categorical definitions. However, the clarity and theoretical basis of these definitions varied considerably .
The theoretical model that was used in the process of formulating the draft definition is a model of determinants and indicators of public health status . It was derived from the Dutch Public Health Status and Forecasts Report, which contains a large amount of up-to date information about Dutch public health status, prevention and health care, and includes international and regional comparisons . Four indicators of the population state of health are distinguished (see Fig. 1): (1) diseases and health conditions, (2) functioning and quality of life, (3) mortality, (4) health and life expectancy. The last three indicators are consequences of diseases and health conditions. Determinants, also called risk factors, aetiological factors or prognostic factors, are causally related to the presence or the course of a (disease or chronic) condition . These determinants can be internal, such as a genetic predisposition, or external factors, such as environmental pollution. Some chronic conditions can also be a risk factor for another chronic condition; for example, diabetes mellitus is a risk factor for cardiovascular disease.
It was our aim to develop a new definition of chronic conditions that can be used in large epidemiological studies. Therefore, based on the theoretical framework, we decided to develop a definition based on medical diagnoses, and not on the consequences of the disease, such as functional limitations or special health care needs. This is in line with most of the available epidemiological studies in the Netherlands, which are diagnosis-based.
Next, the definition must be comprehensive, i.e. not only encompassing the most prevalent conditions, but all possible conditions, however uncommon, somatic as well as psychiatric. Furthermore, it was stated in advance that the definition is explicitly not intended to be used for the legal justification of rights or duties of individuals; for example, for gaining social or financial support.
The consensus procedure consisted of two written consultation rounds and one meeting, in which the draft definition was discussed. The first draft definition to be discussed in the consensus procedure was based on the definitions that came closest to our prerequisites, i.e. “objective” and “comprehensive,” and on the theoretical model shown in Fig. 1. In the first consultation round, several questions were asked in order to obtain insight into the experts’ ideas about the proposed concept. A second round was evaluated and adapted to the experts’ comments in a similar way, and a third proposal was discussed in a consensus meeting to which all experts were invited.
Twenty-seven national clinical and research experts, including a representative of a comprehensive patient and parent organisation, were approached to join the consensus procedure. They were selected either because of their expertise on the subject as a researcher and as a representative of one of the eight academic paediatric departments in the Netherlands, or as a representative of a national institute or organisation that is involved in the research or the care for children with chronic conditions, such as the Dutch Pediatric Association (NVK), Dutch Youth Health Care, the National Institute for Public Health and the Environment (RIVM), the Netherlands Institute for Health Services Research (NIVEL), the Dutch College of General Practitioners (NHG), the Dutch Genetic Alliance (VSOP) and TNO Quality of Life Work and Employment and TNO Quality of Life Prevention and Health.
After reaching consensus about the definition, it was operationalised by three paediatricians, who were not involved in the consensus procedure, and who reviewed all diagnoses listed in ICD-10 together during an informal process .