An overview of the International Disease Classification System with emphasis on the ICD 11 and its implications

The international classification of diseases ICD is a globally used tool by the medical fraternity for diagnosis in epidemiology, health management and clinical purposes. Originally designed as a healthcare classification system it is maintained by the World Health Organization (WHO) under the United Nations Systems, which encompasses a system of diagnostic codes for diseases, nuanced classification of a variety of clinical signs, symptoms, complaints, social circumstances, abnormalities and external causes of injury or disease [1].

A six character-long code may be generated for any such ailment comprising of its generic category, specific variations, thus mapping the health conditions of an individual or community. The system finds use globally by other health administration systems and healthcare services for morbidity and mortality statistics, reimbursement schemes, as well as automated decision systems employed in medical healthcare.[2][3]

HISTORY

The ICD is published by the WHO with the latest being in 1992 titled ICD-10, with updated modifications introduced over certain periods of time, depending upon nuances in a particular field, simplification of pre-existing classification systems or treatment needs. However, as of January 2022, an updated ICD-11 has been put into effect, which had been adopted by the World Health Assembly (WHA) on May 25, 2019. However, the historical basis of this classification system dates back to the latter half of the 19th century with healthcare stalwarts in the field such as Florence Nightingale and Jacques Bertillon.[1][2][5]

Nightingale in 1860 called for a methodical approach in recording healthcare data across hospitals, and the proposal led to the development of systematic data collection. Bertillon 1893 presented the Bertillon Classification of the Causes of Death that was presented and approved at the congress of the International Statistical Institute, held in Chicago that year.

The system was based on the principle of distinguishing the causes of death from general causes to diseases limited to affecting a single organ or anatomical site in the body. The system originally had 44 titles and was adopted wholly by the City of Paris in the year of its inception, however, as other countries began to adopt the system, significant modifications were done which led to the system comprising over 161 titles; a resultant from the revisions and incorporations by the English, German and Swiss systems[4][5].

On the advice of the American Public Health Association (APHA), the systems were adopted by Canada, Mexico and the United States in 1898. The APHA also recommended this system be updated every 10 years to keep in line with the advancements in medical technology. This practice was continued since 1900, as ICD-1.

No significant modifications were made to the publication every decade with a few minor changes recorded tabularly and alphabetically in a small book. This was maintained by a mixed committee of representatives from both the International Statistical Institute and Health Organization under the League of Nations. [4]

This all changed in 1949, with the advent of the 6th volume of the system, i.e., ICD-6, were in the addition of morbidity and mortality statistics, and the title was modified to reflect this change; International Classification of Diseases, Injury and Causes of Death. The WHO had in the previous year (1948) assumed responsibility for the publication of the ICD every decade, following through for the next two iterations ICD-7 and ICD-8 in 1958 and 1967 respectively, before concluding that a 10-year revision for such a classification system was too short for the rate of advancing medical technology at the time.[4]

ICDYEARICD-11900ICD-21910ICD-31921ICD-41930ICD-51939ICD-61949ICD-71957ICD-81968ICD-91979ICD-101999ICD-112022

TABLE-1: A BROAD HISTORICAL TIMELINE FOR ALL VERSIONS OF THE ICD SINCE INCEPTION

Several modifications were made in and after the publications of ICD-9 and ICD-10 pertaining to the healthcare systems adopted by the US, Canadian, Australian and other governments suiting their needs over both healthcare-related statistics as well as the state reimbursement and claim systems introduced and in vogue during the time.[1][4]

ADOPTION AND MODIFICATIONS

Although the WHO published the ICD nearly every decade, some countries require modifications before they may implement it. For instance, with the advent of ICD-9, a separate supplemental document was published in separate fascicles known as the International Classification of Procedures in Medicine, abbreviated as ICPM, which enlisted codes for surgical procedures.

This system however was introduced by the United States, whereas a separate procedure list had been included in the ICD in all its previous versions. Several countries across the globe now use a translated and/or modified version of this ICPM in some capacity or the other. [2]

The International Classification of Disease-Clinical Modifications was also a modified document, created by the National Center for Health Statistics in the United States, which adopts the ICD as well as enlists morbidity data into the system. [4]

Similarly, after the publication of the ICD-10, the clinical modifications counterpart ICD-10-CM was slow to be adopted by the National Centre for Health Statistics in the United States. This was due to governmental policies of Medicare and Medicaid following the ICM-9-CM for the healthcare industry across the country. This resulted in a mixed system comprising morbidity details being based on ICD-9-CM whereas the mortality statistics were based on the ICD-10 without clinical extensions.

The system was re-updated in October 2013, where the existing ICD-9-CM codes had to be interchanged with that of the ICD-10-CM, however, the delays in congressional debates resulted in the actual implementation of the system being delayed by a year to October 2014. [4]

Canada also adopted a modified system for recording its health statistics titled ICA-10-CA that extends beyond hospital healthcare services into risk factors such as socio-economical factors, psychological factors, occupational factors, environmental factors and lifestyle. This aided the Canadian Institute for Health Information to record morbidity classification, extending beyond the scope of simple acute hospital healthcare. [2]

ICD-10: ADOPTION AND REPLACEMENT

The work on ICD-10 began in 1983 and was endorsed by the 43rd World Health Assembly in 1990. It is the 10th modification of the original ICD upheld by the League of Nations pre-World War II. The base document enlists about 14000 codes to encompass new diagnoses as compared to its predecessor the ICD-9 which had only about a few thousand base codes.

The clinical modification of the ICD-10 however enlists upwards of about 70000 codes including health statistics, morbidity, mortality and procedural codes. It allows for tracking the specificity of disease, through the use of optional sub-classification systems, the cause, manifestation, location, severity and type of disease. It has 22 chapters enlisting a wide array of diseases denoted in specific codes of alpha-numeric type. [8]

CHAPTERBLOCKTITLEIA00-B99Certain infectious and parasitic diseasesIIC00-D48NeoplasmsIIID50-D89Diseases of blood & blood-forming organs and certain disorders involving the immune mechanismIVE00-E90Endocrine, nutritional and metabolic diseasesVF00-F99Mental and behavioral disordersVIG00-G99Diseases of the nervous systemVIIH00-H59Diseases of the eye and adnexaVIIIH60-H95Diseases of the ear and mastoid processIXI00-I99Diseases of the circulatory systemXJ00-J99Diseases of the respiratory systemXIK00-K93Diseases of the digestive systemXIIL00-L99Diseases of the skin and subcutaneous tissueXIIIM00-M99Diseases of the musculoskeletal system and connective tissueXIVN00-N99Diseases of the genitourinary systemXVO00-O99Pregnancy, childbirth and the puerpuremXVIP00-P96Certain conditions originating in the perinatal periodXVIIQ00-Q99Congenital malformations, deformations and chromosomal abnormalitiesXVIIIR00-R99Symptoms, signs and abnormal laboratory and clinical findings, not elsewhere classified XIXS00-T98Injury, poisoning and certain other consequences of external circumstancesXXV01-Y98External causes of morbidity and mortalityXXIZ00-Z99Factors influencing health status and contact with health servicesXXIIU00-U99Codes for special purposes

TABLE-2: ICD-10 LIST OF CHAPTERS AND CODES

The common complaints in the United States about the ICD-10-CM are

1) The long list of potentially relevant codes for a given condition (such as rheumatoid arthritis) can be confusing and reduce efficiency

2) The assigned codes for seldom seen conditions [8]

Thus this system was replaced by the ICD-11 which has been in effect since January 2022.

ICD-11

It is the 11th revision of the International Classification of Diseases which has been in effect since January 2022. The development of this iteration was started in 2007 and spanned the expertise of 300 specialists from 55 countries divided into 30 workgroups. An alpha version was drafted in 2011 followed by a beta draft in 2012. The stable draft was released in June 2018 and endorsed by the WHO members in the 72nd World Health Assembly in May 2019.

It consists of about 85000 entities also termed as classes or nodes. An entity, relevant to healthcare may range from a disease or a pathogen to an isolated symptom or a developmental anomaly or disability. The ICD-11 has a foundation component that entails the basis of the WHO Family of International Classification (WHO-FIC) which assigns alphanumeric codes to a particular entity depending upon the parent and child nodes it has been taken from.

The ICD-11 is thus also termed as ICD-11 MMS, to prevent confusion from the foundation document, which also encompasses diseases, disorders, body parts, bodily functions, the reasons for a visit to a healthcare facility, medical procedures, and microbes, the causes of death and social circumstances of the patient.

The foundation document includes chapters from ICD-11 MMS, ICF and ICHI. It is thus a multidimensional collection of entities. An entity can have multiple parents and child nodes. For example, pneumonia can be categorized as a lung infection, but also as a bacterial or viral infection (i.e. by site or by etiology). Thus, the node Pneumonia (entity id: 142052508) has two parents:

Lung infections (entity id: 915779102) and certain infectious or parasitic diseases (entity id: 1435254666). The Pneumonia node in turn has various children, including bacterial pneumonia (entity id: 1323682030) and Viral pneumonia (entity id: 1024154490). The node classification should however not be confused with entity ID.

The ICD-11 can thus be analyzed on the basis of the following headings

• Structure
• Chapters included
• Notable changes from ICD-10

STRUCTURE

The WHO Family of International Classifications is a family of classification systems that include the International Classification of Disease, International Classification of Functioning, Disability and Health (ICF) and International Classification of Health Intervention (ICHI). This forms the foundation of the 11th ICD which encompasses a multi-dimensional approach to the classification of disease, disability, symptoms, socio-economic conditions, morbidities and so on which is the core of all other referenced and derived classification systems.

The derived classification systems are usually tailored pertaining to a particular specialty which guarantees consistency. Such classifications are listed as a tabular or hierarchical form having single parent nodes that entail every enlisted entity as mutually exclusive of each other. Such a form of classification is also referred to as linearization. [11]

CHAPTERS

The chapters included in ICD-11 MMS are the primary linearization of the foundation component in ICD 11. Unlike the ICD-10 codes, the ICD-11 MMS codes never contain the letters I or O, to prevent confusion with the numbers 1 and 0.The list of chapters is as follows;

CHAPTERBLOCKTITLE11A00–1H0ZCertain infectious or parasitic diseases22A00–2F9ZNeoplasms33A00–3C0ZDiseases of blood or blood forming organs44A00–4B4ZDiseases of the immune system55A00–5D46Endocrine, nutritional or metabolic diseases66A00–6E8ZMental, behavioral or neurodevelopmental disorders77A00–7B2ZSleep-wake disorders88A00–8E7ZDiseases of the nervous system99A00–9E1ZDiseases of the visual system10AA00-AC0ZDiseases of the ear or mastoid process11BA00-BE2ZDiseases of the circulatory system12CA00-CB7ZDiseases of the respiratory system13DA00-DE2ZDiseases of the digestive system14EA00-EM0ZDiseases of skin15FA00-FC0ZDiseases of the musculo-skeletal system or connective tissue16GA00-GC8ZDiseases of the genitourinary system17HA00-HA8ZConditions related to sexual health18JA00-JB6ZPregnancy, childbirth or the puerperium19KA00-KD5ZCertain conditions originating in the perinatal period20LA00-LD9ZDevelopmental anomalies21MA00-MH2YSymptoms, signs or clinical findings, not elsewhere classified22NA00-NF2ZInjury, poisoning or certain other consequences of external causes23PA00-PL2ZExternal causes of morbidity or mortality24QA00-QF4ZFactors affecting health status or contact with healthcare services25RA00-RA26Codes for special purposes26SA00-SJ3ZSupplementary Chapter Traditional Medicine Conditions Module-127VA00-VC50Supplementary section for functioning assessment (in line with WHODAS2)28XExtension codes

TABLE-3: LIST OF ICD-11 CHAPTERS

CHANGES

A host of changes are evident between the ICD-10 and ICD-11. These changes are effected under numerous categories with several implications. Broadly they may be studied under the following heads;

• General
• Mental health
• Burn out
• Sexual health
• GLASS
• Traditional medicine
• Miscellaneous

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