This section provides an overview of:

• Precoordinated Expressions

• Postcoordinated Expressions

Why is this important?

SNOMED CT provides a mechanism that enables clinical phrases to be represented, even when a single SNOMED CT concept does not capture the required level of detail. This is important as it enables a wide range of clinical meanings to be captured in a record, without requiring the terminology to include a separate concept for every detailed combination of ideas that may potentially need to be recorded. Application software that supports the use of SNOMED CT expressions enables detailed clinical information to be recorded, retrieved and analyzed.

What is this?

Clinical expressions using SNOMED CT concepts can be of two types: precoordinated expressions, which use a single SNOMED CT concept identifier; and postcoordinated expressions, which contain more than one SNOMED CT identifier.

SNOMED CT support of the postcoordination technique allows additional clinical detail to be represented if required. Postcoordination greatly increases the depth of detail that SNOMED CT can represent without having to include every possible specific site for every possible disorder via a concept. For example, the concept |bacterial pneumonia| has a defining relationship specifying its |causative agent| as |bacteria| and this can be refined to |streptococcus pneumoniae|.

SNOMED CT expressions are a structured combination of one or more concept identifiers used to represent a clinical idea in a logical manner, which is automatically processable. Expressions are represented using the SNOMED CT compositional grammar, which is a lightweight syntax for the representation of SNOMED CT expressions.

The logic on which the SNOMED CT concept model is based allows alternative representations of the same or similar information to be recognized and compared.

Precoordinated expressions are expressions that represent the meaning of individual concepts which are predefined in SNOMED CT. Besides the unique concept identifier and descriptions, each concept also has a formal logic definition represented by a set of defining relationships to other concepts. The figure below shows the precoordinated expression used to record |fracture of tibia|. It illustrates that this can be represented by a single identifier, with or without an accompanying human-readable term. It also illustrates the defining relationships of the concept identified in the expression. This is the precoordinated definitional knowledge which is conveyed by this expression.

The second example shown below illustrates the fact that some SNOMED CT concepts provide quite a lot of detailed refinement, some of which might otherwise be captured separately. We will return to this example when considering postcoordination.

Example: Precoordinated representation of "Laparoscopic emergency appendectomy" SNOMED CT contains the concept 174041007 |laparoscopic emergency appendectomy|. The identifier of this concept (174041007) can be used (with or without the associated term) as a precoordinated expression to record an instance of this procedure. The procedure 'laparoscopic emergency appendectomy' has at least three distinct facets: 'excision of appendix', 'using a laparoscope' as 'emergency procedure'. The SNOMED CT concept 174041007 |laparoscopic emergency appendectomy| precoordinates these facets as its definition includes the following defining relationships:

• 116680003 |is a| = 71388002 |procedure|

• 260870009 |priority| = 25876001 |emergency|

• 424226004 |

Expressions that contain two or more concept identifiers are referred to as postcoordinated expressions. Postcoordination combines concepts and allows more detail to be added to the meaning represented by a single concept. A postcoordinated expression is not just a list of concept identifiers, it follows a set of rules that mimic the way attributes and values are used to define SNOMED CT concepts.

Example: Postcoordinated representation of "Laparoscopic emergency appendectomy"

Although SNOMED CT contains the concept |laparoscopic emergency appendectomy|, it is also possible to represent this clinical phrase using the following postcoordinated expression.

• 6025007 |laparoscopic appendectomy| : 260870009 |priority| = 25876001 |emergency|

This postcoordinated expression has exactly the same meaning as the precoordinated expression

• 174041007 |laparoscopic emergency appendectomy|

The fact that the two expressions have the same meaning can be computed because

• 174041007 |laparoscopic emergency appendectomy| is a defined subtype descendant of 6025007 |laparoscopic appendectomy|; and

• the only differences between the defining attributes of these concepts are the addition of

  • 260870009 |priority|

The example above shows that postcoordination can be applied even when a single concept is available to represent the required meaning. However, the real strength of postcoordination is that it allows a clinical phrase to be represented even when the precise concept is not present in SNOMED CT. In these cases, postcoordinated refinements can be applied to an existing concept to more precisely capture the required meaning.

Example: Postcoordinated representation of "Intolerance to histamine"

SNOMED CT does not contain a concept that represents this clinical idea. However, it is possible to represent it using the following postcoordinated expression. 782197009 |intolerance to substance| : 47429007 |associated with| = 54235008 |histamine|.

Postcoordinated expressions may be created at run-time by selection of individual facets of a concept. For example, to indicate the nature and location of a fracture for a particular bone and, where relevant, whether the bone affected is on the right or left. Some applications allow generation of postcoordinated expression using natural language processing. Alternatively, postcoordinated expression can be selected during user interface design and bound to simple data entry options. In these cases, the user may not be aware that the information is being captured in a postcoordinated form.

There are several valid ways to represent and store postcoordinated expressions. However, to support interoperability, SNOMED International has specified a standard SNOMED CT compositional grammar form that is both human-readable and computer processable. The examples of expression that you see in this guide use this grammar.

The basics of SNOMED CT compositional grammar

• At its simplest level a single SNOMED CT concept identifier is a valid expression.

  • 80146002

• A concept identifier can optionally be followed by a term associated with that concept enclosed between two pipe characters

The refinements used in postcoordinated expressions should follow the same concept model rules that are applied when concepts are defined. Attributes should only be applied to concepts that are in the specified 'domain' for that attribute. The values applied to attributes should be limited to the specified 'range' for that attribute. These rules may sometimes seem to limit flexibility but these rules are important, because if they are followed, it is possible to compute similarities and subtype relationships between different expressions. This ability to compute subtypes is the key to effective meaning-based retrieval of postcoordinated expressions.

Example: Postcoordination and concept model rules A disease with a particular morphological abnormality at a particular site is represented in the following way:

• 64572001 |disease| : {363698007 |finding site| = 91723000 |anatomical structure|, 116676008 |associated morphology| = 49755003 |morphologically abnormal structure|}

It must not be represented in other ways that conflict with concept model rules such as:

• 49755003 |morphologically abnormal structure| : 363698007 |finding site| = 91723000 |anatomical structure|

• 64572001 |disease| : 363698007 |finding site| = (91723000 |anatomical structure| : 116676008 |associated morphology

In some cases, postcoordination may be simply a matter of choosing one of the subtypes of a defining attribute value. For example the definition of |total replacement of hip| includes the attribute |direct device| with the value |hip prosthesis, device|. The subtypes of this value include different types of prosthesis, e.g. |Exeter total hip prosthesis|, |Charnley total hip prosthesis|. One of these more specific values can be selected to specify the type of prosthesis actually used.

In the same way clinical situations, such as family history, can be recorded for any disorder and are not limited to a predefined set of conditions.

Example: Postcoordination of family history

The definition of |family history of disorder| includes 246090004 |associated finding| = 246090004 |disease|. This value can be refined to refer to a particular disease. For example:

• 281666001 |family history of disorder| : 246090004 |associated finding| = 22298006 |myocardial infarction|

The definition of |family history of disorder| specifies that the |subject relationship context| is |person in the family|. This value indicates that the finding applies to a family member rather than the patient and can be refined to refer to a particular family member. For example:

• 281666001 |family history of disorder| : {246090004 |associated finding| = 22298006 |myocardial infarction|, 408732007 |subject relationship context| = 66839005 |father|}

For further information on Postcoordination see

SNOMED CT expressions support consistent and comparable representation of meaning using both precoordinated and postcoordinated expressions. This facilitates retrieval of all instances of expressions that match a set of criteria specified using the subtype hierarchy and other defining relationships.

Example: Emergency procedures If there was a requirement to retrieve all emergency procedures the first step would be to establish the criteria for inclusion. The requirement could be expressed as follows.

• 373110003 |emergency procedure| and all its subtypes

In some cases, it is simply a question of looking at the subtype hierarchy. For example

• 174041007 |laparoscopic emergency appendectomy| is the source of a sequence of |is a| relationships which lead to 373110003 |emergency procedure|.

In other cases, it is necessary to look at the definition of |emergency procedure| and compare this with the equivalent expression. |emergency procedure| is defined as follows:

• 71388002 |procedure| : 260870009 |priority| = 25876001 |emergency|

Therefore, queries looking for instances of emergency procedures should also retrieve postcoordinated expressions in which both of the following are true:

• The focus concept is a subtype of 71388002 |procedure|

• The attribute 260870009 |priority| is present with the value 25876001 |emergency| or a subtype of that concept.

This rule would include postcoordinated representations, for which there is no existing SNOMED CT concept, that have attribute 260870009 |priority| with the value 25876001 |emergency| or a subtype of that concept.

The following graphics illustrate the ways in which query predicates based on SNOMED CT concept definitions can be used to retrieve data based on different criteria. In each case, the data retrieved includes expressions that either have attributes matching the criteria or refer to a concept with defining relationships that match the query criteria.

Example: Result of retrieving concepts with |associated morphology| specified as |benign neoplasm|

Example: Result of retrieving concepts with |finding site| specified as |kidney|

This section provides an overview of:

• How is SNOMED CT used?

• Implementation Examples

  • Clinical Record Applications

  • Clinical Decision Support

  • Enabling Interoperability

  • Reporting

• SNOMED CT in action

Realization of the benefits described in , depends on using the terminology in software applications. The extent of benefits realization depends on the effectiveness of implementation and the way SNOMED CT is used within the system and by users and organizations.

SNOMED CT itself is only a part of the solution to addressing the requirements for effective electronic clinical records. A terminology on its own 'does nothing'. To benefit from a terminology, it must be implemented and used as part of an application. The design of the software application in which it is used, and the objectives and motivation of its users, are key factors in determining success.

SNOMED CT is useful for clinical documentation, as it supports the representation of detailed clinical information, in a way that can be processed automatically. Realization of the capability of SNOMED CT to support clinical information and meaning based retrieval requires careful consideration of the actual setting, in terms of scope of use, record structure, data entry, data retrieval and communication.

SNOMED CT can be implemented in a wide range of clinical record applications. These include systems developed for use with other code systems that have been adapted to support SNOMED CT as well as systems designed with the assumption that SNOMED CT would serve as the primary terminology. The SNOMED CT features that applications support and use may vary, partly due to differences in user requirements and partly due to development priorities.

A terminological resource is only one part of a software application. The functions required to implement a terminology can be divided into:

• Terminology services: Functions that can be performed without reference to data stored in a particular application record structure.

• Record services: Functions that involve storing, retrieving or processing application data (e.g. patient health records).

Different applications may make use of different aspects of SNOMED CT. Applications that only require SNOMED CT for a very limited range of uses and may not require all the features of SNOMED CT. However, by using SNOMED CT, these applications benefit from an enhanced ability to exchange data with other more terminology rich applications. These applications can also evolve to meet emergent requirements by making increasing use of the power of SNOMED CT.

Most users only require a small subset of the content of SNOMED CT. However, use of a terminology that spans a wide range of specialties delivers the benefits that arise from consistency, and interoperability.

Clinical decision support is defined broadly as a clinical system application or process that helps health professionals make clinical decisions to enhance patient care. An example of clinical decision support would be the use of alerts to identify specific clinical contraindications in the administration of thrombocytopenia therapy after a stroke.

The use of SNOMED CT makes clinical information available in a computable form which can be queried and used to trigger decision support rules and prompts. The hierarchies of SNOMED CT enable complex reasoning to support decision support rules. For example, in SNOMED CT the concept |stroke| is synonymous with |cerebrovascular accident| and subsumes all lower level concepts including |paralytic stroke|, |thrombotic stroke| etc. This means that decision support queries are easier to develop and implement because they do not need to identify all the individual terms and codes which may be relevant.

Yes. SNOMED CT is known to be used for Clinical Decision Support in a number of organizations including Kaiser Permanente, Duke University Medical Hospital in the US; National Health Service Hospitals in the UK and Hospital Italiano in Buenos Aries, Argentina.

Kaiser Permanente has a central terminology service which develops and maintains clinical decision support rules and prompts. These can be quickly distributed for implementation throughout the organization. In addition to using this type of approach for clinical decision support, Kaiser Permanente also use it to identify potential cohorts for clinical trials etc.

Information can be recorded using SNOMED CT concepts and descriptions that are independent of the clinical information system being used and either independent of or tied to the context of use, depending on the user requirements. SNOMED CT is a common clinical terminology covering a wide range of requirements and its use. SNOMED CT allows meaning-based computation to be applied to information in messages sent between systems, and provides a foundation for interoperable interpretation of clinical information.

For example, subtype descendant concepts that may be relevant to prescribing decisions (e.g. |allergic disposition|, |kidney disease|) can be used to trigger alerts and reminders in the recipient system, such as medication allergy alerts and drug level investigation warnings. These preventative health care reminders, enable the quality of care to be improved.

Yes. In the United States, Kaiser Permanente (KP), The Veterans Health Administration (VHA), and the Department of Defense (DoD) health systems interoperate using SNOMED CT. A consortium comprised of Kaiser Permanente, the Mayo Clinic, Intermountain Health Care, Geisinger Health System, and Group Health Cooperative of Puget Sound has announced they will interoperate using SNOMED CT and techniques established by KP, the VHA and DoD.

Information encoded as SNOMED CT concepts is semantically consistent. In other words, there is one unique SNOMED CT identifier representing each separate meaning. This lends itself to reporting through specifying the SNOMED CT identifiers of interest. SNOMED CT supports recording at appropriate levels of detail and using relevant terms. This also means that reports can be generated at the appropriate levels of detail using relevant terms for display in the report.

The hierarchical nature of SNOMED CT means that information can be aggregated at the appropriate levels of generalization. That same information can also be used in reporting to provide the same level of detail. SNOMED CT is a common clinical terminology covering a wide range of requirements and supporting a wide variety of use cases for reporting, including patient care, clinical audit, quality improvement, outcomes, epidemiology, patient safety, etc. As SNOMED CT is a clinical terminology with a global scope, reports using SNOMED CT can be compared across boundaries.

Where required, SNOMED CT may also be mapped to other code systems and classifications to support existing reporting requirements.

Yes, many clinical information systems use SNOMED CT to varying degrees and many standards mandate or recommend that SNOMED CT be used. Such cases include reports sent using HL7 messages, microbiology results reporting, and genetic database reports.

You can see other examples of implementations using SNOMED CT in a dynamically maintained list at . This site also allows you to add summaries of implementations that you are involved in.

This section provides an overview of:

• Extension Content

• Reference Sets

Why is this important?

SNOMED CT is designed to allow the International Edition to be enhanced by adding Extensions that address national or local requirements. Additional content required to support national, local or organizational needs that may not have international relevance or may not meet the editorial guideline for inclusion in the International Edition.

SNOMED CT design also includes the Reference Set mechanism which provides a standard way to customize and enhance content for use in a particular country, language, specialty, application or context. Reference Sets developed nationally or locally can modify search and display of content from the International Edition as well as enhancing Extension content.

Many clinical concepts are relevant in all countries, organizations and specialties but some concepts are relevant only to a particular environment. SNOMED CT is designed to allow the International Edition to be enhanced by adding Extensions to meet national or local requirements without compromising the main body of SNOMED CT. This is intended to meet the needs of different specialties and countries, regions, vendors and healthcare institutions.

Extensions are managed by Members or Affiliates who have been issued with a Namespace Identifier. A Namespace Identifier distinguishes the Identifiers of the Components created by an organization. The responsibilities of organizations that create an Extension and provide it for use by other organizations include:

• Maintaining Concept, Descriptions, Relationships, and Reference Sets that they create.

• Inactivating these components as appropriate (duplication, ambiguous, outdated, etc.)

The Concepts, Descriptions, Relationship and Reference Sets that form an Extension use a namespace identifier, which ensures that their SNOMED CT identifier is different from components in:

• SNOMED CT International Release,

• Other SNOMED CT Extensions

The namespace identifier is part of the component identifier. Therefore, components are distinguishable not only in the thesaurus, but also when stored in a patient record, query or decision support protocol.

Extensions use the same file structure as the core International Release. This ensures that:

• SNOMED CT enabled implementations can benefit from the content in these Extensions without the need for any additional software development;

• The same application software can be used to enter, store and process information from different extensions;

• Reference Sets can be constructed that refer to content from the International Release and a variety of Extensions.

Software applications should allow the users or user communities to specify the Extensions to be recognized by their systems.

An Extension should only be recognized if:

• It has been supplied by SNOMED International or another organization authorized by SNOMED International to provide such Extensions;

• The recognizing organization is satisfied with the quality control procedures of the providing organization.

The fact that an organization is permitted to produce Extensions does not imply a seal of approval of the quality of Extensions that organization produces. Therefore a person or organization that authorizes or installs an Extension does so entirely at their own risk.

SNOMED CT has a broad clinical coverage and includes a depth of detail appropriate to a range of health care disciplines and clinical specialties. As a result, it has extensive content, different parts of which are needed in particular environments. The SNOMED CT design includes the Reference Set mechanism, which provides a standard way to refer to a set of SNOMED CT components and to add customized information to a component.

Organizations implementing SNOMED CT benefit from Reference Sets because they allow requirements for use of particular descriptions and concepts to be represented in a standard form that can be applied to any SNOMED CT enabled application. This allows Reference Sets to be shared throughout and between organizations, even when different software is used to meet local or departmental requirements.

Software developers and vendors benefit because Reference Sets provide a common, machine processable representation of requirements for different patterns of use of SNOMED CT. This simplifies local configuration and enhances interoperability with other SNOMED CT enabled applications.

Reference sets can be used for many different purposes, including:

• Language and dialects are represented as Language Reference Sets (see ).

• Maps to and from other code systems and classifications are represented as Simple, Complex or Extended Map Reference Sets (see ).

• Subsets of concepts, description or relationships are represented as Simple Reference Sets. The only information that a Simple Reference Set provides is that a component is part of this subset. Subsets may be used for a variety of general and specific purposes, some of which are identified in the following examples.

• Excluding content

  • Reference sets can be used to exclude concepts that are not required by a particular use case.

• Including content

• National, jurisdictional or organizational requirements

  • Collecting particular minimum sets of data using specific codes.

• Regional variations in disease prevalence

Generic data structures for Reference Sets have been used to create a simple core structure that can be extended to meet a variety of requirements. This has been done rather than developing a complex and inextensible structure that can only be used in a finite and constrained number of ways to enforce editorial policy.

Creating a new Reference Set requires access to a namespace in order to generate SNOMED CT Ids. Within that namespace, at least one module ID concept (with an FSN and Preferred Term) should be added under the |module| sub-hierarchy (within the Core Metadata) for each of the authoring organizations. The steps required to create a new reference set include:

1. Create the Reference Set Concept in the Foundation Metadata hierarchy.

2. Define the Reference Set Attributes within the metadata hierarchy.

3. Create the Descriptor for the Reference Set (by adding members to the Reference Set Descriptor Reference Set).

Please note that step 2 does not need to be performed if using one of the standard Reference Set types that have been predefined in the international release of SNOMED CT. The Reference Set Attributes for these predefined Reference Set types have already been added to the international release.

It is recommended that for each reference set, there is formal documentation that records (at a minimum) the rules, principles and approach used to determine the members of that reference set.

Reference Sets need to be maintained and the content re-examined when new releases of SNOMED CT are made available. Processes need to be established to address the concepts that have become inactive and the new concepts added in each new release.

This section provides an overview of:

• Requirements for translations and language preferences

• Translation approaches

• How SNOMED CT represents translations

Why is this important?

The basic objective of any SNOMED CT translation is to provide accurate and unambiguous descriptions of SNOMED CT concepts in the target language.

SNOMED CT is a multinational, multilingual terminology. It has a built-in framework to manage different languages and dialects. Today, SNOMED CT is available in several languages, including US English, UK English, Spanish, Danish and Swedish, and more translations are continuously being done by member countries.

The goal of any SNOMED CT translation is to provide accurate representations of SNOMED CT concepts in a way that is understandable, usable, and safe. Translations must be concept-based, as term-to-term translations may yield literal expressions that are often meaningless. Instead, the translator analyses each concept based on the position within the hierarchy, the descriptions, and relationships to other concepts before deciding on the most meaningful translation of a concept. SNOMED International provides guidelines to support countries undertaking translations.

SNOMED CT translation is an interdisciplinary collaboration which requires careful attention to content, structure and clinical relevance. These factors are of foremost importance in order to ensure the usability of the terminology in connection with implementation in electronic health record systems. Both linguistic and semantic quality must be assured.

The core SNOMED CT structure and content continue to evolve. These facts call for vigilance on the part of the translation team members who need to review and analyses the relationships of each concept in order to elucidate the meaning of a term within the terminological context. Looking at the preferred term in English is not sufficient to enable accurate concept-based translation.

Close collaboration between specialists in health informatics, linguistics and terminology is essential for the translation process. A translation based solely on linguistic, morphological-syntactical analysis might result in a seemingly correct term which may not adequately represent the concept in question, nor be used by healthcare professionals. On the other hand, compliance with linguistic, systematic, and orthographic principles is necessary in order to avoid confusion and ensure the practical applicability of the terminology.

It is crucial that those involved in the translation, verification, validation, and approval processes are familiar with the terminological principles on which SNOMED CT is based. It is equally important that they comply with SNOMED International Editorial Guide and that they are conscious of issues such as the choice of lexical variant, term requirements, translation techniques, and the importance of ensuring linguistic consistency.

Additionally, it is important that those involved in the translation process are aware that sometimes, their inability to understand a given term or concept may be caused not by their own lack on insight, but actually an ambiguity in the core terminology (international release) that needs to be corrected. SNOMED CT undergoes constant improvement, corrections are made, and ambiguities are addressed. To ensure this constant enhancement of SNOMED CT, any translation team should register questions, comments or suggestions and forward these to SNOMED International in order to avoid spending extra time on unsolvable issues and at the same time contribute to improvement of the terminology. Currently, questions and remarks from the translation teams are dealt with by the SNOMED International request submission process.

From a practical perspective, the deliverables from SNOMED CT translation include:

• Descriptions – each of which contains a term in the target language which accurately reflects the meaning of the concept with which it is associated.

• A Language Reference Set – containing references to each of the descriptions and an indication of whether it is preferred or acceptable for use in the particular language or dialect.

This approach allows the same descriptions to be used in other local variants of the language. In this case another Language Reference Set is provided indicating which descriptions contain the preferred and acceptable terms. Descriptions not referenced by a Language Reference Set are not used in that language or dialect.

This section provides an overview of:

• SNOMED International

• Members and National Release Centers

• SNOMED International Forums, Advisory Group and Special Interest Groups

• SNOMED International Collaborative

SNOMED International is the not-for-profit organization that owns and administers SNOMED CT, and owns the rights to SNOMED CT and related terminology standards. What is this?

SNOMED International the trading name of IHTSDO is an association governed by a General Assembly that contains one representative of each of its national Members.

SNOMED International seeks to improve the health of humankind by fostering the development and use of suitable standardized clinical terminologies, notably SNOMED CT, in order to support safe, accurate, and effective exchange of clinical and related health information. The focus is on enabling the implementation of semantically accurate health records that are interoperable.

The purpose of SNOMED International is to develop, maintain, promote and enable the uptake and correct use of its terminology products in health systems, services and products around the world, and undertake any or all activities incidental and conducive to achieving the purpose of the Association for the benefits of the members.

The bodies and forums of SNOMED International are the foundation for the continuous maintenance, development and distribution of SNOMED CT, and they provide the organizational framework for communication and collaboration between the different parts of the SNOMED community.

SNOMED International current members can be found at the SNOMED International web page (). Members can be either an agency of a national government or another body endorsed by an appropriate national government authority within the country it represents. SNOMED International welcomes new Members.

Members pay a fee, based on national wealth, to SNOMED International which gives them the right to a seat on the General Assembly. SNOMED International does not charge Affiliate Licensees for use of the SNOMED CT International Edition within Member countries. Licensing is also free in the poorest countries and for certain approved public-good uses in other countries. In other cases, low-cost per-institution charges apply to the use of SNOMED CT in operational systems involved in data creation and/or analysis. All use of SNOMED CT is subject to the acceptance of the terms of the SNOMED CT Affiliate License agreement () and the terms of sublicenses issued to end-user organizations by Affiliate Licensees. Members may also impose additional conditions on use of SNOMED CT within their countries. For example, a Member may require licensees to support and include its National Extension in its implementations.

Members undertake a range of activities related to their involvement in SNOMED International and their role in distributing, extending and supporting the use of SNOMED CT in their country. The organization or agency that coordinates this role in each country is referred to as a National Release Centre (NRC). National Release Centers provide a single point of contact for communications with SNOMED International and other Members. Within their own countries, NRCs manage the use of SNOMED CT and communicate with a range of stakeholders, including SNOMED CT Affiliate Licensees, healthcare institutions, clinical groups and end users.

An overview of SNOMED International governance and advisory structures are shown in the following figure.

The General Assembly is the highest authority in SNOMED International and contains one representative from each of its national Members. The General Assembly is collectively responsible for assuring that the Purpose, Objects and Principles of the Association are pursued and that the interests of SNOMED International are safeguarded. It can make binding decisions regarding all matters relating to SNOMED International, subject to and in accordance with the provisions of the Articles of Association, such as budget, work plan and strategic goals. It is recommended though not required that General Assembly representatives attend all meetings. Face-to-face meetings occur usually twice per year with occasional teleconferences and electronic voting.

The Management Board is appointed by the General Assembly. The Management Board directs the Association and has the responsibility for key business decisions. It has at least four face-to-face meetings per year with occasional teleconferences between these meetings.

The Management Board also appoints the Chief Executive Officer (CEO), who has day-to-day responsibility for running the organization. A Senior Management Team, with members each responsible for a particular line of business, supports the CEO and directs the work of employees.

Each Member is entitled to nominate two representatives to the Member Forum (MF). The MF acts as a non-voting advisory body to the CEO and Senior Management Team.

The MF is also a means for optimizing the collaboration and coordination among SNOMED International Member countries provides a means for Members to have discussions on specific Member issues. Moreover, the MF facilitates contact and communication between countries with similar foundations, needs, priorities, etc. It is recommended that each Member gets involved in the MF.

The MF can raise issues of concern to the CEO and Senior Management Team and is also requested to provide specific feedback on national priorities and other matters. The MF is the conduit for communicating widely on consultations that SNOMED International may undertake. These consultations may include specific issues related to SNOMED CT content or SNOMED International documents, products and services. The MF is also a key player in determining which SNOMED International work items should be undertaken and prioritized.

Advisory Groups were established in June 2015 to conduct specific activities that contribute to the fulfillment of the Senior Management Team's responsibilities or the organization's mandate. They are meant to be agile, given the changing needs and direction of the organization, therefore, each group is reviewed on an annual basis to determine if it is still required or if changes in the Terms of Reference are needed. Generally, Advisory Group members have specific skills and abilities related to that particular group.

The role of each Advisory Group is to provide advice to the applicable Senior Management Team member(s) on specific areas that are included in the Terms of Reference to further the knowledge and direction of the organization. At the beginning of each year, each Advisory Group develops a group work plan outline, determines whether Task and Finish sub-groups are required, outlines any resource requirements needed, and lays out a set of measures in order to monitor the progress of the applicable group work plan. The organization, with the approval of the Management Board, may elect to seek approval for separate budget items in the annual budget to assist the Advisory Groups in the completion of their approved work plans. All work plans are to be submitted to the CEO annually for review and approval.

NRCs should note that Advisory Group members are selected by two different nomination processes. The Terms of Reference of each Advisory Group describes which of the two is relevant (or if a combination of the two is used).

Member-based nominations

Member-based nominations are used when SNOMED International seeks to create a forum for SNOMED International staff to work closely with Members. Under this system, Members nominate representatives to serve on an Advisory Group, so the Advisory Group members represent their countries. Typically the Senior Management Team member who chairs the Advisory Group contacts the General Assembly and Member Forum representatives in May or June and invites them to nominate representatives with a particular skill set. SNOMED International then accepts all of those nominees or a subset of them. Any travel expenses of the Advisory Group members to attend approved face-to-face events are then assumed to be the responsibility of the Member. A Member's refusal or inability to pay these expenses does not invalidate or prejudice the nomination in any way, and teleconferencing for those who cannot attend in person is a typical option.

Standard nominations

Other Advisory Groups rely on a standard, open, skills-based nomination process. Advisory Group members selected through this process may submit to SNOMED International any approved travel expenses for reimbursement to attend approved face-to-face Advisory Group events (the SNOMED International Travel Policy has more information about approved expenses and means of submission).

Can Members nominate individuals to serve on Advisory Groups that utilize the standard nomination process? Yes. For example, a Member may nominate its NRC IT expert to serve on the Modeling Advisory Group, which uses the standard nomination process. SNOMED International may select them based on their skills. Who then pays for the travel expenses to attend an Advisory Group face-to-face meeting? The elected person would be entitled (but not required) to submit their expenses for reimbursement from SNOMED International, on the basis that they are serving on the Advisory Group as an expert, and not as a Member representative.

Table 1: Advisory Groups and their Nomination Processes

More information about Advisory Groups can be found at .

Clinical input to support the development of SNOMED CT is delivered through Clinical Reference Groups. These groups are focused on clinical specialities, with each specialty are having its own Confluence based site. Each site supports discussion and knowledge sharing. Access to the Clinical Reference Groups is though a central Confluence portal focused on clinical engagement activities at .

SNOMED International arranges two events a year. In April it holds a Business Meeting and in October a second Business Meeting is combined with the annual SNOMED CT EXPO.

SNOMED International Business Meetings include face-to-face meetings of SNOMED International Governance Bodies and Advisory Groups. Business Meetings may also include face-to-face meetings of some Project Groups and Clinical Reference Groups.

While meetings of Advisory Groups are open to observers, some sessions of other groups are closed and may only be attended by members of the relevant bodies.

A key part of each Business Meeting is the open meeting of the General Assembly, where the key strategic decisions, plans and achievements are made and announced.

Confluence is an online forum/space where the people within SNOMED International Governance and Advisory Bodies can communicate and share information. Confluence facilitates a range of types of communications, including written discussions, meeting announcements and document sharing.

Members, Affiliates, or other interested parties can gain access to the Collaborative Space to learn more about SNOMED International and SNOMED CT. The Confluence space also enables participation in Advisory Groups, Clinical Reference Groups and Project Groups.

Information about Confluence is available at .

Goals and Objectives

The vision for the SNOMED CT Starter Guide is for it to be a practical and useful starting point from which anyone with a general interest in healthcare information can begin learning about SNOMED CT.

Target Audience

The target audience for this Starter Guide includes people from various disciplines who may be involved at any point in the SNOMED CT information management cycle – from initial planning, clinical content definition and implementation through to use of the resulting clinical information. This spans people involved with planning and deciding to proceed and resource a SNOMED CT implementation, people involved in reference set development, terminology management, technical implementation and all aspects of deployment and use. It also includes people involved in clinical information retrieval, analyses, decision support and other aspects of knowledge representation. The characteristics common to all members of the target audience are that they have a reason for wanting to understand SNOMED CT and are seeking a high-level initial overview of topics of which they need to be aware. The Starter Guide does not provide in depth knowledge but does provide an informative and authoritative foundation on which to build.

Topics

The topics covered in this SNOMED CT Starter Guide include:

• SNOMED CT Benefits

• Using SNOMED CT in Clinical Information

• SNOMED CT Basics

• SNOMED CT Logical Model

• SNOMED CT Concept Model

• Expressions SNOMED CT Expressions

• Content Development

• Extension and Customization

• Translation and Language Preferences

• Mapping

• Release Schedule and File Formats

• Implementation

• SNOMED International

• Learning More

For each topic the questions addressed include:

• Why is this important?

• What is this?

Supporting references are included in the final chapter of the guide.

This section provides an overview of:

• Concept Model – Top Level Hierarchies

• Concept Model Attributes – Representing Characteristics of a Concept

Why is this important?

The SNOMED CT concept model specifies the way in which SNOMED CT concepts are defined using a combination of formal logic and editorial rules. Concept model rules specify the top level concepts under which concepts are arranged in the subtype hierarchy and the types of relationships that are permitted between concepts in particular branches of the hierarchy.

What is this?

Concept Model – Top Level Hierarchies

The top of the SNOMED CT hierarchy is occupied by the root concept (|SNOMED CT concept|). All concepts are descended from this root concept through at least one sequence of |is a| relationships. This means that the root concept is a supertype of all other concepts and all other concepts are subtypes of the root concept.

The direct subtypes of the root concept are referred to as 'Top Level Concepts'. These concepts are used to name the main branches of the hierarchy. Each of these Top Level Concepts, together with their many subtype descendants, forms a major branch of the SNOMED CT hierarchy and contains similar types of concepts. As the hierarchies descend (that is, more |is a| relationships are added below the Top Level Concepts) the concepts within them become increasingly specific.

Below is a list of the Top Level Concepts with a brief description of the content represented in their branch of the hierarchy.

• |Clinical finding| represents the result of a clinical observation, assessment or judgment and includes normal and abnormal clinical states (e.g. |asthma|, |headache|, |normal breath sounds|). The |clinical finding| hierarchy includes concepts used to represent diagnoses.

• |Procedure| represents activities performed in the provision of health care. This includes not only invasive procedures but also administration of medicines, imaging, education, therapies and administrative procedures (e.g.

SNOMED CT attributes (or relationship types) are used to represent a characteristic of the meaning of a concept. SNOMED CT currently uses more than one hundred defining attributes when defining the meaning of concepts. Each SNOMED CT attribute can be applied to concepts in one or more branches of the hierarchy. The set of concepts to which an attribute can be applied is called the 'domain' of the attribute. The permitted set of values for each attribute is called the 'range' of the attribute.

The domain is the hierarchy to which a specific attribute can be applied.

For example:

The domain of the attribute |associated morphology| is the |clinical finding| hierarchy. Therefore, a |procedure| cannot have an |associated morphology|. However, a |procedure| can have a |procedure morphology|.

The range is the set of SNOMED CT concepts or concrete values that are allowed as the value of a specified attribute.

For example:

The range for the attribute |associated morphology| is the concept |morphologically abnormal structure| and its subtype descendants. The range for the attribute |finding site| is |anatomical or acquired body structure| and its subtype descendants in the |body structure| hierarchy.

Examples of the domain and range specified for the attributes |finding site| and |laterality|

Some SNOMED CT attributes (or relationship types) have a hierarchical relationship to one another. The hierarchy formed from such relationships is known as an 'attribute hierarchy'. In an attribute hierarchy, one general attribute is the parent of one or more specific subtypes of that attribute. Subtypes of a concept defined using the more general attribute can be defined using a more specific subtype of that attribute. For example, |after|, |causative agent| and |due to| are subtypes of |associated with|, because they have a more specific meaning.

SNOMED CT is an evolving terminology, which means that the attributes used to define concepts in specific hierarchies may change over time. Additionally, editorial principles, that are specified to ensure consistent representation of the same type of concepts may also change. When authoring SNOMED CT content, it is therefore important to always refer to the current SNOMED CT Editorial Guide. The Editorial Guide specifies the attributes that are valid to use within each hierarchy and the valid values that can be assigned to each attribute. It also presents general editorial rules for SNOMED CT content, along with specific guidance on authoring concepts within each hierarchy.

The Machine Readable Concept Model (MRCM) represents rules in the SNOMED CT concept model in a form that can be read by a computer and applied to test that concept definitions and expressions comply with the rules. The MRCM may be used for a variety of purposes, including the authoring and validation of SNOMED CT concepts, expressions, expression constraints and queries, Natural Language Processing and terminology binding to support semantic interoperability. For further information, please visit the guide on the Machine Readable Concept Model or visit the MRCM Browser.

The SNOMED CT defining attributes are used to represent the meaning of concepts in many hierarchies, for example:

• Clinical finding concepts

• Procedure concepts

For further information, please refer to the SNOMED CT Editorial Guide.

Below is a list of some of the attributes used to define |clinical finding| concepts, and a brief description of their meaning:

|Finding site| specifies the body site affected by a condition.

|Associated morphology| specifies the morphologic changes seen at the tissue or cellular level that are characteristic features of a disease.

|Associated with| represents a clinically relevant association between concepts without either asserting or excluding a causal or sequential relationship between the two.

|After| represents a sequence of events where a clinical finding occurs after another |clinical finding| or |procedure| or |event|.

|Due to| relates a |clinical finding| directly to a cause such as another |clinical finding| or a |procedure|.

|Causative agent| identifies the direct causative agent of a disease such as an |organism|, |substance| or |physical force|. (Note: This attribute is not used for vectors, such as mosquitos transmitting malaria).

|Severity| used to sub-class a |clinical finding| concept according to its relative severity.

|Clinical course| represents both the onset and course of a disease.

|Episodicity| represents episodes of care provided by a physician or other care provider, such as a general practitioner. This attribute is not used to represent episodes of disease experienced by the patient.

|Interprets| refers to the entity being evaluated or interpreted, when an evaluation, interpretation or judgment is intrinsic to the meaning of a concept.

|Has interpretation| when grouped with the attribute |interprets|, designates the judgment aspect being evaluated or interpreted for a concept. (e.g. presence, absence etc.)

|Pathological process| provides information about the underlying pathological process of a disorder, i.e. it describes the process that results in the structural or morphologic change.

|Occurrence| refers to a specific period of life during which a condition first presents.

|Finding method| specifies the means by which a clinical finding was determined. This attribute is frequently used in conjunction with |finding informer|.

|Finding informer| specifies the person (by role) or other entity (e.g. a monitoring device) from which the clinical finding information was obtained. This attribute is frequently used in conjunction with |finding method|.

Below is a list of some of the attributes used to define |procedure| concepts, and a brief description of their meaning:

|Procedure site| describes the body site acted on or affected by a procedure.

|Procedure morphology| specifies the morphology or abnormal structure involved in a procedure.

|Method| represents the action being performed to accomplish the procedure. It does not include the surgical approach, equipment or physical forces.

|Procedure device| describes the devices associated with a procedure.

|Access| describes the route used to access the site of the procedure.

|Direct substance| describes the |substance| or |pharmaceutical / biologic product| on which the procedure's method directly acts.

|Occurrence| refers to a specific period of life during which a procedure is undertaken.

|Priority| refers to the priority assigned to a procedure.

|Has focus| specifies the |clinical finding| or |procedure| which is the focus of a procedure.

|Has intent| specifies the intent of a procedure.

|Recipient category| specifies the type of individual or group upon which the action of the procedure is performed.

|Revision status| specifies whether a procedure is primary or a revision.

|Using substance| describes the substance used to execute the action of a procedure, but it is not the substance on which the procedure's method directly acts.

|Using energy| describes the energy used to execute an action.

For attribute values or range, please consult the Editorial Guide (refer to section on , then the appropriate Attributes Summary) or the .

This section provides an overview of:

• Release schedule and process

• Release files and formats

• Release types

Why is this important?

SNOMED CT is distributed to Members and Affiliate Licensees as a set of downloadable files. Those wishing to implement SNOMED CT in software applications should understand the release schedule and the structure and content of the release files. Users should be aware that regular updates of SNOMED CT are made available and should be used in their systems to benefit from continuous improvements to coverage and quality.

The SNOMED CT International Edition is currently released monthly on the last day of each month. The release files are made available to Members in advance of the formal release date and Affiliate Licensees gain access either through their National Member or via the SNOMED International Affiliate Licensing system. Many Members supplement the International Edition with releases of their national Extension. The Extensions may be released at the same time as the International Edition but in some cases are released on different dates and at different intervals.

Release Format 2 (RF2) is the primary format used for SNOMED CT release files. This format includes valuable additional data that was not supported by the earlier format.

The SNOMED CT International Edition is released as a set of files:

• The release files are:

  • Tab-delimited text files

  • Encoded in accordance with the Unicode UTF-8 specification (which supports a wide range of characters, symbols and accented characters)

All components in the release files have permanent unique SNOMED CT Identifiers.

• There are also individual files with specified columns for each type of Reference Set

  • These files contain essential information about language preferences, subsets, maps and metadata to support technical implementations

The same file formats are also used for SNOMED CT Extensions.

The RF2 specification provides a history tracking mechanism within the distributed files. This enables different release types to be provided using the same file format and utilizing this mechanism to optimize installation and updating.

Full Release: A 'Full' release contains every version of every component that has ever been released prior to or in the specified Edition. This release provides a full historical record and can be used to obtain views of the state of any component at any point in time since its first release. The 'Full' release is the easiest way to install and initialize SNOMED CT. However the files are large and in each release only a small fraction of the content will have changed.

Delta Release: A 'Delta' release contains only those component versions created, inactivated or changed since the previous release. The 'Delta' release is much smaller than a 'Full' release and is ideal for updating a 'Full' release of the previous version. Adding a 'Delta' release to the previous version's 'Full' release will update the installation to a 'Full' release of the current Version. Note that a Delta release is not included as part of the International release but Delta release files can be generated. (See for details.)

Snapshot Release: A 'Snapshot' release contains the most recent version of every component released up to the time of the snapshot. The version of each component contained in a snapshot is the most recent version of that component at the release time. The 'Snapshot' release is useful for a simple installation but does not provide a history or retrospective view of the terminology.

There are valid use cases for each Release Type. Each International release will incorporate the Full and Snapshot Release Types, allowing users to choose the most appropriate format for their needs. Extensions should always be available as a full release and other Release Types may also be made available.

In Snapshot Release files

• Each SNOMED CT concept is held as a single row in the concept file. Each row represents a clinical concept.

• Each description is held as a single row in the description file, and is associated with a single concept.

• Each relationship, from a source concept to a destination concept, is held as a single row in the relationship file. Each row also refers to the concept that represents the relationship type.

In Full Release files, concepts, descriptions and relationships may be represented by more than one row. In this case each row represents the state of the component at a stated point in time.

Documentation

This Starter Guide is intended as a practical and useful starting point from which anyone with a general interest in healthcare information can begin learning about SNOMED CT. It provides a broad overview of SNOMED CT from which to start a more detailed exploration of areas that are of particular interest. Besides from the Starter Guide, SNOMED International provides a range of formally approved specifications and practical guidance documents. These can be accessed from the online document library.

Courses

SNOMED International provides online courses, tutorials and other materials that are designed to enable you to learn more about SNOMED CT. Additionally, we offer completion certificates to those who pass course assessments. To find out more about these education services please visit https://www.snomed.org/education on the SNOMED International website. For access to courses, tutorials and other educational materials go to the SNOMED CT E-Learning Server.

SNOMED CT Expo

The SNOMED CT Expo is an open event for anyone interested in SNOMED CT and practical applications of the terminology. The event includes invited keynote speakers and several tracks of peer-reviewed presentations about SNOMED CT in general with a focus on implementation experiences and developments that facilitate more effective use of the terminology.

The Expo also includes tutorials and workshops for those seeking greater understanding of SNOMED CT, an exhibition of vendor products that use SNOMED CT and a range of poster presentations on related topics.

The Expo is the main annual event in the SNOMED International calendar for anyone interested in the use and development of the global healthcare terminology. In addition to the scheduled sessions, it provides an excellent opportunity to network with others with a shared interest in SNOMED CT.

Watch past Expo recordings -

Information about SNOMED International Find out more about the organization, members, newsletter and events.

General information about SNOMED CT Materials include a benefits and information about licensing.

Documentation Library Access to a wide range of documents about SNOMED CT.

SNOMED CT Browsers A range of online and offline tools to search SNOMED CT content.

SNOMED CT in Action Examples of how SNOMED CT is being used around the world.

SNOMED CT Vendor Guide

The Vendor Introduction to SNOMED CT provides an informative practical introduction to SNOMED CT focused primarily on the needs of vendors and developers of EHRs.

SNOMED CT National Release Center Guide

Provides an introduction to SNOMED International and SNOMED CT for those working in or planning to development a National Release Center.

SNOMED CT Implementation Support Portal A dedicated portal to support SNOMED CT implementations.

SNOMED CT E-Learning Server Sign up for SNOMED CT courses or see publicly accessible presentations.|

This section provides an overview of:

• Mapping approaches

• How SNOMED CT represents maps

• Steps in a mapping process

The SNOMED CT Starter Guide is designed as a practical introduction for anyone interested in understanding SNOMED CT, the global standard for clinical terminology. Its goal is to provide a high-level, accessible overview that helps readers begin exploring how SNOMED CT supports effective healthcare information management.

Provide Feedback

This section provides an overview of:

• How SNOMED CT supports reuse of clinical information

• Extent of practical use

• Approaches to implementation

• Lessons learnt

• Challenges

The objective of SNOMED International and all users of SNOMED CT is to facilitate the accurate recording and sharing of clinical and related health information and the semantic interoperability of health records.

SNOMED CT is a clinical terminology with global scope covering a wide range of clinical specialties, disciplines and requirements. As a result of its broad scope, one of the benefits of SNOMED CT is a reduction of specialty boundary effects that arise from use of different terminologies or coding systems by different clinicians or departments. This allows wider sharing and reuse of structured clinical information. Another benefit of SNOMED CT is that the same data can be processed and presented in ways that serve different purposes. For example, clinical records represented using SNOMED CT can be processed and presented in different ways to support direct patient care, clinical audit, research, epidemiology, management and service planning. Additionally, the global scope of SNOMED CT reduces geographical boundary effects arising from the use of different terminologies or coding systems in different organizations and countries.

With SNOMED CT, clinical information is recorded using identifiers that refer to concepts that are formally defined as part of the terminology. SNOMED CT supports recording of clinical information at appropriate levels of detail using relevant clinical concepts. The structures of SNOMED CT allow information to be entered using synonyms that suit local preferences while recording the information in a consistent and comparable form. Additionally, the hierarchical nature of SNOMED CT permits information to be recorded with different levels of detail to suit particular uses (e.g. |pneumonia|, |bacterial pneumonia| or |pneumococcal pneumonia|). SNOMED CT also allows additional detail to be added by combining concepts where the available concepts are not sufficiently precise. SNOMED CT allows a range of different options for immediate retrieval and subsequent reuse to address immediate and longer term clinical requirements and the requirements of other users. The nature of SNOMED CT hierarchies allow information to be selectively retrieved and reused to meet different requirements at various levels of generalization (e.g. retrieval of subtypes of |lung disorder| or |bacterial infection| would both include |bacterial pneumonia|).

The SNOMED CT concept model also allows additional details to be considered when retrieving data. For example, the concept |pneumococcal pneumonia| specifies that the |causative agent| is |streptococcus pneumoniae| and this allows the organism causing this disease to be analyzed.

Many systems use SNOMED CT to represent some types of clinical information. The extent of use is varied in terms of:

• The clinical content captured (i.e. what is included and what is not).

• How the structure of this content relates to the structures in the records.

• The scope and consistency of use and reuse (i.e. within and across national and local organizations, across departments, within proprietary applications or specifically configured instances of proprietary applications).

SNOMED CT has been implemented in a variety of ways which differ in the extent to which they harness particular features of the terminology. In some cases, these differences merely reflect the specific requirements of a particular use. Other factors include the design of existing systems prior to the introduction of SNOMED CT, sophistication of available technology and support for a range of other health informatics standards.

Key determinants for effective benefits realization include:

• Representation of stored clinical information.

  • To enable effective reuse of clinical information, SNOMED CT should be used within a record structure (or information model) that stores similar information consistently and in ways that can be readily queried.

• Ease of data entry

The features of SNOMED CT support reusability of clinical information. However, reusability also requires a consistent structured representation of clinical information that complements the meaning supported by SNOMED CT. Without this, overlaps and conflicts between structural and terminological representations of clinical content can result in ambiguous and potentially conflicting interpretations.

The way in which the use of terminology and structure together contribute to the representation of meaningful information is sometimes referred to as the "model of meaning". To enable widespread clinical information reuse, queries need to be consistently formulated in ways that take account of the way the information is structured and coded. A common model of meaning facilitates widespread reuse of clinical information, ability to reuse queries and a consistent approach to linkage between clinical information and knowledge resources.

Human factors may result in inconsistent recording of similar clinical information. This issue can be minimized by effectively constraining data entry.

An important limitation is the diversity of views related to the structure of clinical information and the overlap between information models and terminology. There are also differing views on application design, different requirements for collection of clinical information and different views on record structures and data entry methods appropriate to different use cases.

SNOMED International is working with other standards bodies including the International Organization for Standardisation (ISO) and Health Level 7 (HL7), as well as various collaborative efforts exploring the relationship between terminology and structured clinical information. The objective is to ensure that the role of SNOMED CT as a key component of clinical information and systems is understood as part of overall efforts towards harmonization and interoperability.

This section provides an overview of how effective use of SNOMED CT:

• Benefits populations

• Benefits individual patients and clinicians

• Supports evidence based healthcare

Why is this important?

Understanding the benefits of SNOMED CT will inform key decisions and the development of strategies for adoption, implementation and use of this clinical terminology.

SNOMED CT supports the development of comprehensive high-quality clinical content in health records. It provides a standardized way to represent clinical phrases captured by the clinician and enables automatic interpretation of these. SNOMED CT is a clinically validated, semantically rich, controlled vocabulary that facilitates evolutionary growth in expressivity to meet emerging requirements.

SNOMED CT based clinical information benefits individual patients and clinicians as well as populations and it supports evidence based care.

The use of an Electronic Health Record (EHR) improves communication and increases the availability of relevant information. If clinical information is stored in ways that allow meaning-based retrieval, the benefits are greatly increased. The added benefits range from increased opportunities for real time decision support to more accurate retrospective reporting for research and management.

SNOMED CT enabled clinical health records benefit individuals by:

• Enabling relevant clinical information to be recorded using consistent, common representations during a consultation.

• Enabling guideline and decision support systems to check the record and provide real-time advice, for example, through clinical alerts.

• Supporting the sharing of appropriate information with others involved in delivering care to a patient through data capture that allows understanding and interpretation of the information in a common way by all providers.

SNOMED CT enabled clinical health records benefit populations by:

• Facilitating early identification of emerging health issues, monitoring of population health and responses to changing clinical practices.

• Enabling accurate and targeted access to relevant information, reducing costly duplications and errors.

• Enabling the delivery of relevant data to support clinical research and contribute evidence for future improvements in treatment.

SNOMED CT enabled health records inform evidence based health care decisions by:

• Enabling links between clinical records and enhanced clinical guidelines and protocols.

• Enhancing the quality of care experienced by individuals.

• Reducing costs of inappropriate and duplicative testing and treatment.

This section provides an overview of:

• SNOMED CT features

• Exploring SNOMED CT

• SNOMED CT design and development

• SNOMED CT components and hierarchies

• SNOMED CT characteristics

• SNOMED CT supporting different languages

• SNOMED CT products and services

An awareness of SNOMED CT features, components, characteristics and products provides an initial foundation on which to build greater understanding. It also informs discussions leading to decisions about adoption, implementation and use of this terminology.

SNOMED CT:

• Is the most comprehensive, multilingual clinical healthcare terminology in the world.

• Is a resource with comprehensive, scientifically validated clinical content.

• Enables consistent, processable representation of clinical content in electronic health records.

When implemented in software applications, SNOMED CT can be used to represent clinically relevant information consistently, reliably and comprehensively as an integral part of producing electronic health information.

Implementation requires an understanding of the way that SNOMED CT content is represented by components and supported by reference sets (Refsets).

While reading the guide, you may find it useful to explore the content of SNOMED CT. You can do this using one of a range of online browsers listed on our web site at . Note that the listed browsers are not endorsed by SNOMED International and they should only be used to a get feel for the content and structure of the terminology. It is useful to experiment with several different browsers as they vary in the way they present particular features of the terminology.

SNOMED CT is a core clinical healthcare terminology that contains concepts with unique meanings and formal logic based definitions organized into hierarchies. SNOMED CT content is represented using three types of components:

• Concepts representing clinical meanings that are organized into hierarchies.

• Descriptions which link appropriate human readable terms to concepts.

• Relationships which link each concept to other related concepts.

These components are supplemented by reference sets, which provide additional flexible features and enable configuration of the terminology to address different requirements.

SNOMED CT concepts represent clinical thoughts, ranging from |abscess| to |zygote|. Every concept has a unique numeric concept identifier. Within each hierarchy, concepts are organized from the general to the more detailed. This allows detailed clinical data to be recorded and later accessed or aggregated at a more general level.

SNOMED CT descriptions link appropriate human readable terms to concepts. A concept can have several associated descriptions, each representing a synonym that describes the same clinical concept. Each translation of SNOMED CT includes an additional set of descriptions, which link terms in another language to the same SNOMED CT concepts. Every description has a unique numeric description identifier.

SNOMED CT relationships link concepts to other concepts whose meaning is related in some way. These relationships provide formal definitions and other properties of the concept. One type of relationship is the |is a| relationship which relates a concept to more general concepts. These |is a| relationships define the hierarchy of SNOMED CT concepts.

• For example, the concepts |bacterial pneumonia| and |viral pneumonia| both have an |is a| relationship to |pneumonia| which has an |is a| relationship to the more general concept |infectious disease of lung|.

Other types of relationships represent aspects of the meaning of a concept.

• For example, the concept |viral pneumonia| has a |causative agent| relationship to the concept |virus| and a |finding site| relationship to the concept |structure of parenchyma of lung|.

Every relationship has a unique numeric relationship identifier.

Reference sets (Refsets) are a flexible standard approach used by SNOMED CT to support a variety of requirements for customization and enhancement of SNOMED CT. These include the representation of subsets, language preferences for use of particular terms and mapping from or to other code systems. Every reference set has a unique numeric concept identifier.

SNOMED CT concepts are organized in hierarchies. Within a hierarchy concepts range from the more general to the more detailed. Related concepts in the hierarchy are linked using the |is a| relationship.

• Examples of some of the hierarchies include |clinical finding|, |procedure|, |observable entity|, |body structure| and |organism|.

SNOMED CT has a broad coverage of health related topics. It can be used to describe a patient's medical history, the details of an orthopedic procedure, the spread of epidemics, and much more. At the same time, the terminology has an unmatched depth, which enables clinicians to record data at the appropriate level of granularity.

Specific applications tend to focus on a restricted set of SNOMED CT, such as concepts related to ophthalmology. These subsets can be used to present relevant parts of the terminology, depending on the clinical context and local requirements. This means for example, that a drop down list to select diagnoses in an electronic health record in a mental health facility can be tailored to that setting. Similarly, subsets can be defined for problem lists for physician specialties or to provide appropriate medication lists for nurses in community care.

When individual jurisdictions have needs beyond those that can be reflected in a global terminology, perhaps due to requirements in local legislation, they can develop local or national extensions. Thus, even though SNOMED CT is global in scope, it can be adapted to each country's or areas requirements. SNOMED CT maps work to provide explicit links to health related classifications and coding schemes in use around the world, e.g. statistical classifications such as ICD-10. Maps to or from several national code systems are also available from, or under development, by Members. Maps to or from clinical domain specific code systems are also maintained by specialty groups with which SNOMED International has collaborative agreement. Maps facilitate reuse of SNOMED CT based clinical data for other purposes, such as reimbursement or statistical reporting.

SNOMED CT is a multinational, multilingual terminology. It has a built-in framework to manage different languages and dialects. The International Release includes a set of language independent concepts and relationships. Today, SNOMED CT is available in many languages that can be viewed in the SNOMED International SNOMED CT Browser. The basic objective of any SNOMED CT translation is to provide accurate representations of SNOMED CT concepts in a way that is understandable, usable, and safe. Translation must be concept based. Translators need to analyse concepts based on the fully specified name and take account of its position within the hierarchy, its descriptions, and its relationships to other concepts. This enables a meaningful translation of a concept based on phrases that are well used and clearly understood in all countries. SNOMED International maintains guidelines and other materials to support countries undertaking translations.

Members and organizations covered by the SNOMED CT Affiliate License have access to a range of products and services, including:

• SNOMED CT terminology files consisting of:

  • Concepts

  • Descriptions

This section provides an overview of:

• SNOMED CT International Release Content Development

• Request Submission

Why is this important?

Understanding the quality and rigor of the approach to SNOMED CT content development ensures user confidence in the quality of the content when implementing or using SNOMED CT.

What is this?

SNOMED CT International Release Content Development

SNOMED CT's content development is based on four basic principles that have and continue to guide development of its clinical content and technical design including:

• Development efforts must encompass broad, inclusive involvement of diverse clinical groups and medical informatics experts.

• The clinical content must be quality focused and adhere to strict editorial rules.

• The quality improvement process must be open to public scrutiny and vendor input, to ensure that the terminology is truly useful within health care applications.

The content of SNOMED CT evolves with each release. The types of changes made include new concepts, new descriptions, new relationships between concepts, and new reference sets, as well as updates and retirement of any of these components. Drivers of these changes include changes in understanding of health and disease processes; introduction of new drugs, investigations, therapies and procedures; and new threats to health, as well as proposals and work provided by SNOMED CT users.

The three basic operational criteria that help determine whether new content is following the principle of creating and sustaining semantic interoperability are that SNOMED CT must be:

• Understandable: The meaning must be able to be communicated, to be understood by an average health care provider without reference to inaccessible, hidden or private meanings.

• Reproducible: It is not enough for one individual to say they think they understand the meaning. It must be shown that multiple people understand the meaning in the same way.

• Useful: The meaning must have some demonstrable use or applicability to health or health care.

Recognizing the goal that SNOMED CT should become the accepted international terminological resource for health care, it must therefore be capable of supporting multilingual terminological renderings of common concepts. For the terminology to be acceptable to the widest possible range of users it must include translations as well as alternative spellings and other variations that arise from a national and regional dialect. Furthermore it must be capable of representing differences between the underlying concepts that arise from cultural, ethnic or linguistic variations.

Clinical terminology development is challenging for a variety of reasons. Even in a single country or language people often use the same words to mean different things, as well as using different words for the same thing. The names assigned to some clinical conditions are sometimes based on an earlier incomplete or erroneous understanding and often these misleading names remain in use long after knowledge has moved on. Progress of medical knowledge and evolution of pathogenic organisms creates a continual, growing requirement to add new content and revise definitions. Efforts by specialty bodies to establish diagnostic criteria and staging scales also lead to changes, and sometimes to divergence between different or overlapping sources of authority. In the face of these challenges, content development is directed to address current and emerging priorities identified by Members and other stakeholders.

Continuous quality improvement is the aim of SNOMED International. Quality processes are included as part of the work completed by the team of modeler's involved in SNOMED CT development. A documented scientific process is followed and content is defined and reviewed by multiple clinician editors. Conflicts between editors are resolved through an iterative process, based on achieving agreement and consensus, before being entered into the terminology. As necessary, the authoring team consult with additional experts to review the scientific integrity of the content.

SNOMED International provides a request submission service to gather and process requests for additions and changes to the content of the SNOMED CT International Edition. This service is directly accessible by National Release Centers (NRC) in Member countries and recognized Terminology Authorities within organizations with whom SNOMED International is actively collaborating. Organizations within Member countries can submit their requests for additions and changes to the National Release Centre. In some cases, requests with particular local relevance may be added to a National Extension. The NRC forwards requests that it considers have international relevance to SNOMED International for a decision. If a request is deemed to have high priority it should result in action in the next release cycle. However, requests that require significant changes that would impact on other content may take longer.

This section provides an overview of:

• Logical Model Components – representing the core content of the terminology

• Reference Sets – configuring and enhancing terminology content

Why is this important?

The SNOMED CT logical model provides the fundamental structure of SNOMED CT and specifies how the components can be managed in an implementation setting to meet a variety of primary and secondary uses.

What is this?

The SNOMED CT logical model defines the way in which each type of SNOMED CT component and derivative is related and represented. The core component types in SNOMED CT are concepts, descriptions and relationships. The logical model therefore specifies a structured representation of the concepts used to represent clinical meanings, the descriptions used to refer to these, and the relationships between the concepts.

Logical Model Overview

Every concept represents a unique clinical meaning, which is referenced using a unique, numeric and machine-readable SNOMED CT identifier. The identifier provides an unambiguous unique reference to each concept and does not have any ascribed human interpretable meaning.

• Other types of components also have unique identifiers – however, the concept identifier has a specific role as the code used to represent the meaning in clinical records, documents, messages and data.

A set of textual descriptions are assigned to every concept. These provide the human readable form of a concept. Two types of description are used to represent every concept - Fully Specified Name (FSN) and Synonym. Additionally a Definition maybe added on a case-by case basis if required.

The FSN represents a unique, unambiguous description of a concept's meaning. The FSN is not intended to be displayed in clinical records, but is instead used to disambiguate the distinct meaning of each different concept. This is particularly useful when different concepts are referred to by the same commonly used word or phrase. Each concept can have only one FSN in each language or dialect.

A synonym represents a term that can be used to display or select a concept. A concept may have several synonyms. This allows users of SNOMED CT to use the terms they prefer to refer to a specific clinical meaning. Concepts can have multiple synonyms, and the associated terms are not necessarily unique – thus two concepts may have the same synonym term. Interpretation of a synonymous term therefore depends on the concept identifier.

Each concept has one synonym which is marked as |preferred| in a given language, dialect, or context of use. This is known as the "preferred term" and is a word or phrase commonly used by clinicians to name that concept. In each language, dialect or context of use, one and only one synonym can be marked as |preferred|. Any number of other synonyms that are valid in a language, dialect or context of use can be marked as |acceptable|.

A Definition is a textual description that has been applied to some SNOMED CT concepts that provides additional information about the intended meaning of the concept.

Example of descriptions for a single concept (US - English)

A relationship represents an association between two concepts. Relationships are used to logically define the meaning of a concept in a way that can be processed by a computer. A third concept, called a relationship type (or attribute), is used to represent the meaning of the association between the source and destination concepts. There are different types of relationships available within SNOMED CT.

Example of attribute relationships

Subtype relationships are the most widely used type of relationship. Subtype relationships use the |is a| relationship type and are therefore also known as |is a| relationships. Almost all active SNOMED CT concepts are the source of at least one |is a| relationship. The only exception is the root concept |SNOMED CT Concept| which is the most general concept. The |is a| relationship states that the source concept is a subtype of the destination concept. SNOMED CT relationships are directional and the |is a| relationship read in the reverse direction states that the destination concept is a supertype of the source concept.

Example of is a relationships

The |is a| relationships form the hierarchies of SNOMED CT. They are therefore also known as hierarchical relationships. The source concept of the |is a| relationship has a more specific clinical meaning than the target concept. This means that the level of clinical detail of the concepts increases with the depth of the hierarchies.

If two concepts are directly linked by a single |is a| relationship, the source concept is said to be a "subtype child" of the destination concept. The destination concept is referred to as a "supertype parent". Any concept that is the source of a sequence of one or more |is a| relationships leading to a specified destination concept, is a "subtype descendant" of that concept. Similarly, any concept that is the destination of a sequence of one or more |is a| relationships leading to a specified source concept, is a "supertype ancestor" of that concept. It is also said that the source concept of an |is a| relationship "is subsumed by" the target concept, and that the target concept of an |is a| relationship "subsumes" the source concept.

Each concept can have |is a| relationships to several other concepts (i.e. a concept may have multiple supertype parent concepts). As a result the SNOMED CT hierarchy is not a simple tree but has a structure that is known as a "polyhierarchy".

Illustration of SNOMED CT subtype hierarchy and terms used to describe it

An attribute relationship contributes to the definition of the source concept by associating it with the value of a defining characteristic. The characteristic (attribute) is specified by the relationship type and the value is provided by the destination of the relationship.

The following example shows the defining relationships of the concept |abscess of heart|. The attribute relationships |associated morphology| and |finding site| are used to associate the source concept |abscess of heart| to respectively the target concepts |abscess|, and |heart structure|.

Example of defining relationships

Unlike |is a| relationships, which are used to define all concepts, the applicability of each type of attribute relationship is limited to a defined domain and range. The domain refers to the concepts that can serve as source concepts for that type of attribute relationship. The range refers to the concepts that can serve as destinations (values) for those attributes. The domain and range specification ensure consistent definitions that can be used to infer additional semantic relationships to deliver reliable meaning-based retrieval of the composed meanings.

The first example below violates the domain constraint of |causative agent|, as descendants of |body structure| are not in the domain of |causative agent|. The second example below is valid with respect to the domain constraint of |causative agent|, because |disorder| is in the domain of |causative agent|. However, this example violates the range constraint of |causative agent|, as descendants of morphological abnormality are not in the range of |causative agent|.

Example of erroneous relationships

In SNOMED CT every concept is specified as either defined or primitive.

A concept is defined if its defining characteristics are sufficient to distinguish its meaning from other similar concepts. One example is that the concept |acute disease| is defined by its two defining relationships. The first relationship is |is a| |disease| and the second relationship is |clinical course| of |sudden onset AND/OR short duration|. Stating that this concept is defined means that any concept that |is a| |disease| and has a |clinical course| of |sudden onset AND/OR short duration| is a subtype of this concept (or the concept itself).

A concept is primitive (not defined) if its defining characteristics are not sufficient to uniquely distinguish its meaning from other similar concepts. One example is that the primitive concepts |disease| and |drug action| share the same defining characteristics: namely a relationship of type |is a| to the concept |clinical finding|. This is despite the fact that the concepts |disease| and |drug action| represent different clinical ideas.

Reference Sets (Refsets) are a standard way to represent additional non-defining information about members of a set of components. Reference Sets are important as they can be used in SNOMED CT enabled applications to constrain, configure and enhance functionality to match requirements for different use cases. Some examples of the many uses of reference sets are to represent:

• Language and dialect preferences for use of particular terms to describe a concept. Language Reference Sets allow the preferred and acceptable descriptions to be configured for a language, dialect or context of use.

• Subsets of components that are included in or excluded from the set of values that can be used in a particular country, organization, specialty or context.

• Value sets of concepts limiting the permitted content of a field in line with requirements of standard message or communication interface.