The International Classification of Diseases (ICD) is the
international "standard diagnostic tool for epidemiology, health
management and clinical purposes". Its full official name is
International Statistical Classification of Diseases and Related
The ICD is maintained by the
World Health Organization
World Health Organization (WHO), the
directing and coordinating authority for health within the United
Nations System. The ICD is designed as a health care classification
system, providing a system of diagnostic codes for classifying
diseases, 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
Diagnostic and Statistical Manual of Mental Disorders (which
is limited to psychiatric disorders), 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 (WHO-FIC).
The ICD is revised periodically and is currently in its tenth
revision. ICD-10, as it is therefore known, is from 1992 and the WHO
publishes annual minor updates and triennial major updates. ICD-11 was
planned for 2017, but has been pushed back to 2018. The ICD is part
of a "family" of guides that can be used to complement each other,
including also the International Classification of Functioning,
Disability and Health which focuses on the domains of functioning
(disability) associated with health conditions, from both medical and
1 Historical synopsis
2 Versions of ICD
2.6 ICD-11 (in development)
3 Usage in the United States
4 Mental health issues
5 See also
7 External links
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In 1860, during the international statistical congress held in London,
Florence Nightingale made a proposal that was to result in the
development of the first model of systemic collection of hospital
data. In 1893, a French physician, Jacques Bertillon, introduced the
Bertillon Classification of Causes of Death at a congress of the
International Statistical Institute in Chicago.
A number of countries and cities 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
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 ten 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
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. 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
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 .
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
See also: List of ICD-8a codes
The Eighth 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 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 USA, 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
[and mortality] statistics in the United States.
See also: List of
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
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
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 Ninth 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
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.
ICD-9 was published by the
World Health Organization
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.
International Classification of Diseases, Clinical Modification
(ICD-9-CM) is an adaption created by the U.S. National Center for
Health Statistics (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 of two or 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
U.S. governmental agencies responsible for overseeing all changes and
modifications to the ICD-9-CM.
Main article: ICD-10
ICD-10 began in 1983, and the new revision was endorsed by the
World Health Assembly
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 155,000 different codes and permits tracking
of many new diagnoses and procedures, a significant expansion on the
17,000 codes available in ICD-9. 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.
Main article: ICD-10-CM
ICD-10-CM was slow in the United States. Since 1979, the
US had required ICD-9-CM codes for Medicare and
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, for diagnosis codes, replaces volumes 1 and 2. Annual
updates are provided.
ICD-10-PCS, for procedure codes, replaces volume 3. Annual updates are
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.
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 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
factors to health, such as occupational and environmental factors,
lifestyle and psycho-social circumstances.
ICD-11 (in development)
World Health Organization
World Health Organization is currently revising the International
Classification of Diseases (ICD) towards the ICD-11. The development
is taking place on an internet-based workspace, called iCAT
(Collaborative Authoring Tool) Platform, somewhat similar to a wiki
– yet it requires more structure and peer review process. The WHO
collaborates through this platform with all interested parties.
The final draft of the ICD-11 system is expected to be submitted to
World Health Assembly
World Health Assembly (WHA) for official endorsement by
2017. The draft review was completed in April 2015 A final
version for approval at the WHA is expected in 2018.
In ICD-11 each disease entity will have definitions that give key
descriptions and guidance on what the meaning of the entity/category
is in human-readable terms, to guide users. This is an advancement
over ICD-10, which had only title headings. The Definitions have a
standard structure according to a template with standard definition
templates and further features exemplified in a "Content Model". The
Content Model is a structured framework that captures the knowledge
that underpins the definition of an ICD entity. The Content Model
therefore allows computerization (with links to ontologies and SNOMED
CT). Each ICD entity can be seen from different dimensions or
"parameters". For example, there are currently 13 defined main
parameters in the Content Model (see below) to describe a category in
An external review of the ICD-11 Revision has been completed. The
report notes the progress in the ICD Revision, and makes clear
recommendations about forward progress in the revision.
ICD Entity Title - Fully Specified Name
Classification Properties - disease, disorder, injury, etc.
Textual Definitions - short standard description
Terms - synonyms, other inclusion and exclusions
Body System/Structure Description - anatomy and physiology
Temporal Properties - acute, chronic or other
Severity of Subtypes Properties - mild, moderate, severe, or other
Manifestation Properties - signs, symptoms
Causal Properties - etiology: infectious, external cause, etc.
Functioning Properties - impact on daily life: activities and
Specific Condition Properties - relates to pregnancy etc.
Treatment Properties - specific treatment considerations: e.g.
Diagnostic Criteria - operational definitions for assessment
ICD-11 invokes a more sophisticated architecture than historical
versions, consistent with its generation as a digital resource. The
core content of the system, called the Foundation Component, is a
semantic network of words and terms, where any given term can have
more than one parent. To address the requirement that statistical
classifications exhibit mutual exclusiveness (so events are not
counted more than once) and exhaustiveness (so there is a place to
tally all events), ICD11 supports the serialization of the Foundation
Component into an arbitrary number of linearizations, optimized for
use cases. The main linearization, presently called the Joint
Morbidity and Mortality Statistics, is the tabular
format with which most traditional users will become familiar.
However, other linearizations, for primary care, multiple
sub-specialty derivatives, or applications such as clinical decision
support are possible. Finally, preliminary work in partnership with
IHTSDO is underway to ensure that the ICD-11 Foundation Component
is semantically coherent through development of the Common Ontology, a
SNOMED CT which will anchor the Foundation Component to
terms defined through description logic.
ICD exists in 41 Languages in electronic versions and its expression
in multiple languages will be systematically pursued in ICD-11.
Usage in the United States
In the United States, the
U.S. Public Health Service
U.S. 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 hospitals. The U.S. 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 U.S. Department of Health and
Human Services and used by hospitals and other healthcare facilities
to better describe the clinical picture of the patient. 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 U.S. 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.
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 (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 (DSM) of the American
Psychiatric Association 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 (scheduled for 2018), 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 [these classifications] are clinically
useful" and recommended that section F66 be deleted for the
An international survey of psychiatrists in 66 countries comparing use
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
Classification of mental disorders
Classification of Pharmaco-Therapeutic Referrals
International Classification of Primary Care (ICPC)
Research Domain Criteria
Research Domain Criteria (RDoC), a framework being developed by the
National Institute of Mental Health
Current Procedural Terminology
MedDRA (Medical Dictionary for Regulatory Activities)
Systematized Nomenclature of Medicine Clinical Terms
Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT)
WHO Family of International Classifications
International Classification of Functioning, Disability and Health
International Classification of Health Interventions
^ "International Classification of Diseases (ICD)". World Health
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^ "About WHO". World Health Organization. Archived from the original
on 9 February 2014. Retrieved 14 March 2014.
^ a b "The WHO Family of International Classifications". World Health
Organization. Archived from the original on 22 December 2013.
Retrieved 14 March 2014.
^ Information from
World Health Organization
World Health Organization (WHO): List of Official
ICD-10 Updates. For the ICD-11 revision: The ICD 11th Revision is due
by 2017 (Archived, Feb. 2014); ICD Revision Timelines and ICD-11 Beta
Draft (online beta-version of ICD-11).
^ a b "History of the development of the ICD" (PDF). Who.int.
Retrieved 11 December 2017.
^ International health statistics using this system are available at
the Global Health Observatory (GHO) and the WHO Statistical
Information System (WHOSIS).
^ Katsching, Heinz (February 2010). "Are psychiatrists an endangered
species? Observations on internal and external challenges to the
profession". World Psychiatry. World Psychiatric Association. 9 (1):
21–28. doi:10.1002/j.2051-5545.2010.tb00257.x. PMC 2816922 .
^ a b c d e
ICD-10 Volume 2, online at http://
^ a b c "International Classification Of Diseases - 9 - CM, (1979)".
Wonder.cdc.gov. Retrieved 11 December 2017.
^ O'Malley KJ, Cook KF, Price MD, Wildes KR, Hurdle JF, Ashton CM
(2005). "Measuring diagnoses: ICD code accuracy". Health Serv Res. 40:
1620–39. doi:10.1111/j.1475-6773.2005.00444.x. PMC 1361216 .
^ World Health Organization. FAQ on ICD. Accessed 12 July 2011.
^ National Center for Health Statistics, CDC. ICD-9-CM Guidelines,
Conversion Table, and Addenda. Classification of Diseases,
Functioning, and Disability. Retrieved 2010-01-24.
^ InstaCode Institute.
Diagnosis Codes - International Classisfication of
Diseases - Medical
Diagnosis Codes". www.findacode.com. Retrieved
^ WHO. International Classification of Diseases (ICD).
^ a b CMS Office of Public Affairs (February 11, 2008). "HHS Proposes
ICD-10 Code Sets and Updated Electronic Transaction
Standards" (Press release). U.S. Department of Health & Human
Services. Retrieved 2009-02-11.
^ New Zealand Health Information Service. ICD-10-AM. Accessed 12 July
^ a b Canadian Institute for Health Information. ICD-10-CA. Archived
2015-05-01 at the Wayback Machine. Accessed 12 July 2011.
^ International Classification Of Diseases - 9 - CM, (1979).
Wonder.cdc.gov. Retrieved on 2014-06-20.
^ "Classification of Diseases, Functioning, and Disability". U.S.
Disease Control. Retrieved 29 October 2010.
^ a b c Initial WHO response to the report of the external review of
the ICD-11 revision. WHO Department of Health Statistics and
Information Systems (12 May 2015) Retrieved on 2015-10-26.
^ "Revision of International Classification Diseases by 2018 - ABC
Live". Abclive.in. Retrieved 11 December 2017.
^ Makary, MA; Daniel, M (3 May 2016). "Medical error—the third
leading cause of death in the US". BMJ: i2139.
^ Moriyama, IM; Loy, RM; Robb-Smith, AHT (2011). Rosenberg, HM;
Hoyert, DL, eds. History of the Statistical Classification of Diseases
and Causes of Death (PDF). Hyattsville, MD: U.S. Department of Health
and Human Services, Centers for
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^ Who Mental Health Evidence And Research (Mer). Who.int. Retrieved
^ Cochran, Susan D.; Drescher, Jack; Kismödi, Eszter; Giami, Alain;
García-Moreno, Claudia; Atalla, Elham; Marais, Adele; Meloni Vieira,
Elisabeth; Reed, Geoffrey M. (2014). "Proposed declassification of
disease categories related to sexual orientation in the International
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672–679. doi:10.2471/BLT.14.135541. PMC 4208576 .
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Note: Since adoption of
ICD-10 CM in the USA, several online tools
have been mushrooming. They all refer to that particular modification
and thus are not linked here.
Official website at
World Health Organization
World Health Organization (WHO)
ICD-10 online browser (WHO)
ICD-10 online training direct access (WHO)
ICD-10-CM (USA – modification) at Centers for
Disease Control and
ICD-11 Beta Draft
Health information management
Clinic management system
Computerized physician order entry
Electronic health record
Health information technology
Hospital information system
Personal health record
Regional Health Information Organization
Consumer health informatics
Public health informatics
Continuity of Care Record
Health Level 7
List of medical and health informatics journals