The World Health Organization International Classification of Diseases (ICD)
The fields of health terminology, classification, ontology, and related information models have evolved dramatically over the last 25 years (1) and the increasing demands and uses of information has also transformed the process of coding. A standard registry of morbidity and mortality data provides health information for statistics and epidemiology, health care management, allocation of resources, monitoring and evaluation of research, and for disease prevention and treatment. This information need has given rise to a process of coding, whereby words describing medical conditions are translated into codes (2).
The International Classification of Diseases (ICD) is maintained by the World Health Organization (WHO) and provides a common language for use worldwide as a diagnostic and classification tool for epidemiology, clinical purposes and health management. It enables the analysis of the general health situation of different population groups and provides data on the key problems to be managed. It is used to classify diseases registries for many types of health and administrative purposes including death certificates and electronic health care records. In addition to enabling the storage and retrieval of diagnostic information for clinical, epidemiological and quality purposes, including the needs of payers and Health Technology Assessment bodies, these reported data also provide the basis for compilation of national mortality and morbidity statistics (MMS) by WHO Member States (2,3).
The first edition of the ICD was published in 1893 (4). This classification distinguished between systemic diseases and those localized to a particular organ or anatomical site (5). The ICD has thus far maintained a similar framework, distributing conditions according to topography (5), with the result that some complex conditions, such as allergies including anaphylaxis, have been poorly represented.
The ICD has been periodically revised, with most countries now using the tenth revision (ICD-10) or national adaptations thereof (3). It is used by more than 100 countries, is available in 43 different languages and is the tool used for allocating about 70% of the world’s health expenditure. In the US alone this amounted in 2017 to USD $ 3.5 trillions according to the National Center for Health Statistics (6-8). Therefore, modification of the ICD framework has the potential to have an impact on health financing and economics. On the other hand, the misclassification or underrepresentation of specific disorders in this global classification system can lead to lack of visibility, investment and public health action, as proved for allergic and hypersensitivity conditions (9,10).