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The International Classification of Diseases (ICD) is a globally used
diagnostic Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine "cause and effect". In systems enginee ...
tool for
epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evi ...
,
health management Health administration, healthcare administration, healthcare management or hospital management is the field relating to leadership, management, and administration of public health systems, health care systems, hospitals, and hospital networks ...
and clinical purposes. The ICD is maintained by the
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
(WHO), which is the directing and coordinating authority for health within the United Nations System. The ICD is originally designed as a
health care Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health pr ...
classification system, providing a system of diagnostic codes for classifying
disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
s, including nuanced classifications of a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. This system is designed to map health conditions to corresponding generic categories together with specific variations, assigning for these a designated code, up to six characters long. Thus, major categories are designed to include a set of similar diseases. The ICD is published by the WHO and used worldwide for morbidity and mortality statistics, reimbursement systems, and automated decision support in health care. This system is designed to promote international comparability in the collection, processing, classification, and presentation of these statistics. Like the analogous ''
Diagnostic and Statistical Manual of Mental Disorders The ''Diagnostic and Statistical Manual of Mental Disorders'' (DSM; latest edition: DSM-5-TR, published in March 2022) is a publication by the American Psychiatric Association (APA) for the classification of mental disorders using a common langu ...
'' (which is limited to psychiatric disorders and almost exclusive to the United States), the ICD is a major project to statistically classify all health disorders, and provide diagnostic assistance. The ICD is a core statistically based classificatory diagnostic system for health care related issues of the
WHO Family of International Classifications A medical classification is used to transform descriptions of medical diagnoses or procedures into standardized statistical code in a process known as clinical coding. Diagnosis classifications list diagnosis codes, which are used to track disease ...
(WHO-FIC). The ICD is revised periodically and is currently in its 11th revision. The ICD-11, as it is therefore known, was accepted by WHO's World Health Assembly (WHA) on 25 May 2019 and officially came into effect on 1 January 2022. On 11 February 2022, the WHO stated that 35 countries were using the ICD-11. The ICD is part of a "family" of international classifications (WHOFIC) that complement each other, also including the International Classification of Functioning, Disability and Health (ICF) which focuses on the domains of functioning (disability) associated with health conditions, from both medical and social perspectives, and the International Classification of Health Interventions (ICHI) that classifies the whole range of medical, nursing, functioning and public health interventions. The title of the ICD is formally the International Statistical Classification of Diseases and Related Health Problems, although the original title, International Classification of Diseases, is still informally the name by which it is usually known.


Historical synopsis

In 1860, during the international statistical congress held in London,
Florence Nightingale Florence Nightingale (; 12 May 1820 – 13 August 1910) was an English social reformer, statistician and the founder of modern nursing. Nightingale came to prominence while serving as a manager and trainer of nurses during the Crimean War ...
made a proposal that was to result in the development of the first model of systematic collection of hospital data. In 1893, a French physician,
Jacques Bertillon Jacques Bertillon (11 November 1851 – 4 July 1922) was a French statistician and demographer. Born in Paris, Bertillon was the son of statistician Louis Bertillon and the older brother of Alphonse Bertillon. He was educated as a physicia ...
, introduced the ''Bertillon Classification of Causes of Death'' at a congress of the
International Statistical Institute The International Statistical Institute (ISI) is a professional association of statisticians. It was founded in 1885, although there had been international statistical congresses since 1853. The institute has about 4,000 elected members from gov ...
in Chicago. A number of countries adopted Bertillon's system, which was based on the principle of distinguishing between general diseases and those localized to a particular organ or anatomical site, as used by the City of Paris for classifying deaths. Subsequent revisions represented a synthesis of English, German, and Swiss classifications, expanding from the original 44 titles to 161 titles. In 1898, the American Public Health Association (APHA) recommended that the registrars of Canada, Mexico, and the United States also adopt it. The APHA also recommended revising the system every 10 years to ensure the system remained current with medical practice advances. As a result, the first international conference to revise the International Classification of Causes of Death took place in 1900, with revisions occurring every ten years thereafter. At that time, the classification system was contained in one book, which included an Alphabetic Index as well as a Tabular List. The book was small compared with current coding texts. The revisions that followed contained minor changes, until the sixth revision of the classification system. With the sixth revision, the classification system expanded to two volumes. The sixth revision included morbidity and mortality conditions, and its title was modified to reflect the changes: International Statistical Classification of Diseases, Injuries and Causes of Death (ICD). Prior to the sixth revision, responsibility for ICD revisions fell to the Mixed Commission, a group composed of representatives from the International Statistical Institute and the Health Organization of the
League of Nations The League of Nations (french: link=no, Société des Nations ) was the first worldwide intergovernmental organisation whose principal mission was to maintain world peace. It was founded on 10 January 1920 by the Paris Peace Conference th ...
. In 1948, the WHO assumed responsibility for preparing and publishing the revisions to the ICD every ten years. WHO sponsored the seventh and eighth revisions in 1957 and 1968, respectively. It later became clear that the established ten year interval between revisions was too short. The ICD is currently the most widely used statistical classification system for diseases in the world. In addition, some countries—including Australia, Canada, and the United States—have developed their own adaptations of ICD, with more procedure codes for classification of operative or diagnostic procedures.


Versions of ICD


ICD-6

The ICD-6, published in 1949, was the first to be shaped to become suitable for morbidity reporting. Accordingly, the name changed from International List of Causes of Death to International Statistical Classification of Diseases. The combined code section for injuries and their associated accidents was split into two, a chapter for injuries, and a chapter for their external causes. With use for morbidity there was a need for coding mental conditions, and for the first time a section on mental disorders was added .ICD-10 Volume 2, online a
Classifications
WHO.int


ICD-7

The International Conference for the Seventh Revision of the International Classification of Diseases was held in Paris under the auspices of WHO in February 1955. In accordance with a recommendation of the WHO Expert Committee on Health Statistics, this revision was limited to essential changes and amendments of errors and inconsistencies.


ICD-8a

The 8th Revision Conference convened by WHO met in Geneva, from 6 to 12 July 1965. This revision was more radical than the Seventh but left unchanged the basic structure of the Classification and the general philosophy of classifying diseases, whenever possible, according to their
etiology Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, ...
rather than a particular manifestation. During the years that the Seventh and Eighth Revisions of the ICD were in force, the use of the ICD for indexing hospital medical records increased rapidly and some countries prepared national adaptations which provided the additional detail needed for this application of the ICD. In the US, a group of consultants was asked to study the 8th revision of ICD (ICD-8a) for its applicability to various users in the United States. This group recommended that further detail be provided for coding hospital and morbidity data. The American Hospital Association's "Advisory Committee to the Central Office on ICDA" developed the needed adaptation proposals, resulting in the publication of the International Classification of Diseases, Adapted (ICDA). In 1968, the United States Public Health Service published the International Classification of Diseases, Adapted, 8th Revision for use in the United States (ICDA-8a). Beginning in 1968, ICDA-8a served as the basis for coding diagnostic data for both official morbidity nd mortalitystatistics in the United States.


ICD-9

The International Conference for the Ninth Revision of the International Statistical Classification of Diseases, Injuries, and Causes of Death, convened by WHO, met in Geneva from 30 September to 6 October 1975. In the discussions leading up to the conference, it had originally been intended that there should be little change other than updating of the classification. This was mainly because of the expense of adapting data processing systems each time the classification was revised. There had been an enormous growth of interest in the ICD and ways had to be found of responding to this, partly by modifying the classification itself and partly by introducing special coding provisions. A number of representations were made by specialist bodies which had become interested in using the ICD for their own statistics. Some subject areas in the classification were regarded as inappropriately arranged and there was considerable pressure for more detail and for adaptation of the classification to make it more relevant for the evaluation of medical care, by classifying conditions to the chapters concerned with the part of the body affected rather than to those dealing with the underlying generalized disease. At the other end of the scale, there were representations from countries and areas where a detailed and sophisticated classification was irrelevant, but which nevertheless needed a classification based on the ICD in order to assess their progress in health care and in the control of disease. A field test with a bi-axial classification approach—one axis (criterion) for anatomy, with another for etiology—showed the impracticability of such approach for routine use. The final proposals presented to and accepted by the Conference in 1978 retained the basic structure of the ICD, although with much additional detail at the level of the four digit subcategories, and some optional five digit subdivisions. For the benefit of users not requiring such detail, care was taken to ensure that the categories at the three digit level were appropriate. For the benefit of users wishing to produce statistics and indexes oriented towards medical care, the 9th Revision included an optional alternative method of classifying diagnostic statements, including information about both an underlying general disease and a manifestation in a particular organ or site. This system became known as the 'dagger and asterisk system' and is retained in the Tenth Revision. A number of other technical innovations were included in the Ninth Revision, aimed at increasing its flexibility for use in a variety of situations. It was eventually replaced by ICD-10, the version currently in use by the WHO and most countries. Given the widespread expansion in the tenth revision, it is not possible to convert ICD-9 data sets directly into ICD-10 data sets, although some tools are available to help guide users. Publication of ICD-9 without IP restrictions in a world with evolving electronic data systems led to a range of products based on ICD-9, such as MeDRA or the Read directory.


ICPM

When ICD-9 was published by the World Health Organization (WHO), the International Classification of Procedures in Medicine (ICPM) was also developed (1975) and published (1978). The ICPM surgical procedures fascicle was originally created by the United States, based on its adaptations of ICD (called ICDA), which had contained a procedure classification since 1962. ICPM is published separately from the ICD disease classification as a series of supplementary documents called fascicles (bundles or groups of items). Each fascicle contains a classification of modes of laboratory, radiology, surgery, therapy, and other diagnostic procedures. Many countries have adapted and translated the ICPM in parts or as a whole and are using it with amendments since then.


ICD-9-CM

''International Classification of Diseases, Clinical Modification'' (ICD-9-CM) is an adaption created by the US
National Center for Health Statistics The National Center for Health Statistics (NCHS) is a U.S. government agency that provides statistical information to guide actions and policies to improve the public health of the American people. It is a unit of the Centers for Disease Control ...
(NCHS) and used in assigning diagnostic and procedure codes associated with inpatient, outpatient, and physician office utilization in the United States. The ICD-9-CM is based on the ICD-9 but provides for additional morbidity detail. It is updated annually on October 1. It consists three volumes: * Volumes 1 and 2 contain diagnosis codes. (Volume 1 is a tabular listing, and volume 2 is an index.) Extended for ICD-9-CM * Volume 3 contains procedure codes for surgical, diagnostic, and therapeutic procedures. ICD-9-CM only The NCHS and the Centers for Medicare and Medicaid Services are the US governmental agencies responsible for overseeing all changes and modifications to the ICD-9-CM.


ICD-10

Work on ICD-10 began in 1983, and the new revision was endorsed by the Forty-third World Health Assembly in May 1990. The latest version came into use in WHO Member States starting in 1994. The classification system allows more than 55,000 different codes and permits tracking of many new diagnoses and procedures, a significant expansion on the 17,000 codes available in
ICD-9 The International Classification of Diseases (ICD) is a globally used diagnostic tool for epidemiology, health management and clinical purposes. The ICD is maintained by the World Health Organization (WHO), which is the directing and coordinati ...
. Adoption was relatively swift in most of the world. Several materials are made available online by WHO to facilitate its use, including a manual, training guidelines, a browser, and files for download. Some countries have adapted the international standard, such as the "ICD-10-AM" published in Australia in 1998 (also used in New Zealand), and the "ICD-10-CA" introduced in Canada in 2000.Canadian Institute for Health Information
''ICD-10-CA''.
Accessed 12 July 2011.


ICD-10-CM

Adoption of ICD-10-CM was slow in the United States. Since 1979, the US had required ICD-9-CM codes for Medicare and
Medicaid Medicaid in the United States is a federal and state program that helps with healthcare costs for some people with limited income and resources. Medicaid also offers benefits not normally covered by Medicare, including nursing home care and per ...
claims, and most of the rest of the American medical industry followed suit. On 1 January 1999 the ICD-10 (without clinical extensions) was adopted for reporting mortality, but ICD-9-CM was still used for morbidity. Meanwhile, NCHS received permission from the WHO to create a clinical modification of the ICD-10, and has production of all these systems: *
ICD-10-CM The ICD-10 Clinical Modification (ICD-10-CM) is a modification of the ICD-10, authorized by the World Health Organization, used as a source for diagnosis codes in the United States of America. It replaces the earlier ICD-9-CM. Adoption Adop ...
, for diagnosis codes, replaces volumes 1 and 2. Annual updates are provided. *
ICD-10-PCS The ICD-10 Procedure Coding System (ICD-10-PCS) is an international system of medical classification used for procedural coding. The Centers for Medicare and Medicaid Services, the agency responsible for maintaining the inpatient procedure code s ...
, for procedure codes, replaces volume 3. Annual updates are provided. On 21 August 2008, the US Department of Health and Human Services (HHS) proposed new code sets to be used for reporting diagnoses and procedures on health care transactions. Under the proposal, the ICD-9-CM code sets would be replaced with the ICD-10-CM code sets, effective 1 October 2013. On 17 April 2012 the Department of Health and Human Services (HHS) published a proposed rule that would delay, from 1 October 2013 to 1 October 2014, the compliance date for the ICD-10-CM and PCS. Once again, Congress delayed implementation date to 1 October 2015, after it was inserted into "Doc Fix" Bill without debate over objections of many. Revisions to ICD-10-CM Include: * Relevant information for ambulatory and managed care encounter. * Expanded injury codes. * New combination codes for diagnosis/symptoms to reduce the number of codes needed to describe a problem fully. * Addition of sixth and seventh digit classification. * Classification specific to laterality. * Classification refinement for increased data granularity.


ICD-10-CA

ICD-10-CA is a clinical modification of ICD-10 developed by the Canadian Institute for Health Information for morbidity classification in Canada. ICD-10-CA applies beyond acute hospital care, and includes conditions and situations that are not diseases but represent
risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often u ...
s to health, such as occupational and environmental factors, lifestyle and psycho-social circumstances.


ICD-11

The eleventh revision of the International Classification of Diseases, or the ICD-11, is almost five times as big as the ICD-10. It was created following a decade of development involving over 300 specialists from 55 countries. Following an alpha version in May 2011 and a beta draft in May 2012, a stable version of the ICD-11 was released on 18 June 2018, and officially endorsed by all WHO members during the 72nd World Health Assembly on 25 May 2019. For the ICD-11, the WHO decided to differentiate between the core of the system and its derived specialty versions, such as the ICD-O for
oncology Oncology is a branch of medicine that deals with the study, treatment, diagnosis and prevention of cancer. A medical professional who practices oncology is an ''oncologist''. The name's etymological origin is the Greek word ὄγκος (''ó ...
. As such, the collection of all ICD entities is called the Foundation Component. From this common core, subsets can be derived. The primary derivative of the Foundation is called the ICD-11 MMS, and it is this system that is commonly referred to and recognized as "the ICD-11". MMS stands for Mortality and Morbidity Statistics. ICD-11 comes with an implementation package that includes transition tables from and to ICD-10, a translation tool, a coding tool, web-services, a manual, training material, and more. All tools are accessible after self-registration from th
Maintenance Platform
The ICD-11 ''officially'' came into effect on 1 January 2022, although the WHO admitted that "not many countries are likely to adapt that quickly". In the United States, the advisory body of the Secretary of Health and Human Services has given an expected release year of 2025, but if a clinical modification is determined to be needed (similar to the
ICD-10-CM The ICD-10 Clinical Modification (ICD-10-CM) is a modification of the ICD-10, authorized by the World Health Organization, used as a source for diagnosis codes in the United States of America. It replaces the earlier ICD-9-CM. Adoption Adop ...
), this could become 2027.


Usage in the United States

In the United States, the US Public Health Service published ''The International Classification of Diseases, Adapted for Indexing of Hospital Records and Operation Classification'' (ICDA), completed in 1962 and expanding the ICD-7 in a number of areas to more completely meet the indexing needs of
hospital A hospital is a health care institution providing patient treatment with specialized health science and auxiliary healthcare staff and medical equipment. The best-known type of hospital is the general hospital, which typically has an emergen ...
s. The US Public Health Service later published the ''Eighth Revision, International Classification of Diseases, Adapted for Use in the United States'', commonly referred to as ICDA-8, for official national morbidity and mortality statistics. This was followed by the ''ICD, 9th Revision, Clinical Modification'', known as ICD-9-CM, published by the US Department of Health and Human Services and used by hospitals and other healthcare facilities to better describe the clinical picture of the
patient A patient is any recipient of health care services that are performed by healthcare professionals. The patient is most often ill or injured and in need of treatment by a physician, nurse, optometrist, dentist, veterinarian, or other heal ...
. The diagnosis component of ICD-9-CM is completely consistent with ICD-9 codes, and remains the data standard for reporting morbidity. National adaptations of the ICD-10 progressed to incorporate both clinical code (ICD-10-CM) and procedure code (ICD-10-PCS) with the revisions completed in 2003. In 2009, the US Centers for Medicare and Medicaid Services announced that it would begin using ICD-10 on April 1, 2010, with full compliance by all involved parties by 2013. However, the US extended the deadline twice and did not formally require transitioning to ICD-10-CM (for most clinical encounters) until October 1, 2015. The years for which causes of death in the United States have been classified by each revision as follows: * ICD-1: 1900 * ICD-2: 1910 * ICD-3: 1921 * ICD-4: 1930 * ICD-5: 1939 * ICD-6: 1949 * ICD-7: 1958 * ICD-8A: 1968 * ICD-9: 1979 * ICD-10: 1999 Cause of death on United States death certificates, statistically compiled by the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
(CDC), are coded in the ICD, which does not include codes for human and system factors commonly called medical errors.


Mental health issues

The ICD includes a section classifying mental and behavioral disorders (Chapter V). This has developed alongside the
Diagnostic and Statistical Manual of Mental Disorders The ''Diagnostic and Statistical Manual of Mental Disorders'' (DSM; latest edition: DSM-5-TR, published in March 2022) is a publication by the American Psychiatric Association (APA) for the classification of mental disorders using a common langu ...
(DSM) of the
American Psychiatric Association The American Psychiatric Association (APA) is the main professional organization of psychiatrists and trainee psychiatrists in the United States, and the largest psychiatric organization in the world. It has more than 37,000 members are invo ...
and the two manuals seek to use the same codes. The WHO is revising their classifications in these sections as part the development of the ICD-11, and an "International Advisory Group" has been established to guide this. Section F66 of the ICD-10 deals with classifications of psychological and behavioural disorders that are associated with sexual development and orientation. It explicitly states that "sexual orientation by itself is not to be considered a disorder," in line with the DSM and other classifications that recognise homosexuality as a normal variation in human sexuality. The Working Group has reported that there is "no evidence that hese classificationsare clinically useful" and recommended that section F66 be deleted for the ICD-11. An international survey of psychiatrists in 66 countries comparing use of the ICD-10 and DSM-IV found that the former was more often used for clinical diagnosis while the latter was more valued for research. The ICD is actually the official system for the US, although many mental health professionals do not realize this due to the dominance of the DSM. A psychologist has stated: "Serious problems with the clinical utility of both the ICD and the DSM are widely acknowledged."


See also

*
Clinical coder A clinical coder—also known as clinical coding officer, diagnostic coder, medical coder, or nosologist—is a health information professional whose main duties are to analyse clinical statements and assign standard codes using a classification ...
* Medical classifications ** Classification of mental disorders **
Classification of Pharmaco-Therapeutic Referrals The ''Classification of Pharmaco-Therapeutic Referrals'' (''CPR'') is a taxonomy focused on defining and grouping together situations requiring a referral from pharmacists to physicians (and vice versa) regarding the pharmacotherapy used by the ...
** International Classification of Primary Care (ICPC) **
Research Domain Criteria The Research Domain Criteria (RDoC) project is an initiative of personalized medicine in psychiatry developed by US National Institute of Mental Health (NIMH). In contrast to the Diagnostic and Statistical Manual of Mental Disorders (DSM) maintai ...
(RDoC), a framework being developed by the National Institute of Mental Health *
Medical diagnosis Medical diagnosis (abbreviated Dx, Dx, or Ds) is the process of determining which disease or condition explains a person's symptoms and signs. It is most often referred to as diagnosis with the medical context being implicit. The information r ...
**
Diagnosis-related group Diagnosis-related group (DRG) is a system to classify hospital cases into one of originally 467 groups, with the last group (coded as 470 through v24, 999 thereafter) being "Ungroupable". This system of classification was developed as a collabora ...
*
Medical terminology Medical terminology is a language used to precisely describe the human body including all its components, processes, conditions affecting it, and procedures performed upon it. Medical terminology is used in the field of medicine Medical terminolog ...
**
Current Procedural Terminology The Current Procedural Terminology (CPT) code set is a procedural code set developed by the American Medical Association (AMA). It is maintained by the CPT Editorial Panel. The CPT code set describes medical, surgical, and diagnostic services and ...
**
MedDRA A subscription-based product of the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH), MedDRA or Medical Dictionary for Regulatory Activities is a clinically validated international medical t ...
(Medical Dictionary for Regulatory Activities) **
Systematized Nomenclature of Medicine Clinical Terms SNOMED CT or SNOMED Clinical Terms is a systematically organized computer-processable collection of medical terms providing codes, terms, synonyms and definitions used in clinical documentation and reporting. SNOMED CT is considered to be the mo ...
(SNOMED CT) *
WHO Family of International Classifications A medical classification is used to transform descriptions of medical diagnoses or procedures into standardized statistical code in a process known as clinical coding. Diagnosis classifications list diagnosis codes, which are used to track disease ...
** International Classification of Functioning, Disability and Health ** International Classification of Health Interventions


References


External links

Note: Since adoption of ICD-10 CM in the US, several online tools have been mushrooming. They all refer to that particular modification and thus are not linked here. * at World Health Organization (WHO)
ICD-10 online browser
(WHO)
ICD-10 online training direct access
(WHO)

(USA – modification) at Centers for Disease Control and Prevention (CDC)
ICD-11 release

ICD-11 maintenance
{{Authority control Classification of mental disorders Data coding framework Diagnosis classification Statistical data coding World Health Organization