Messages and communication services are a means of exchanging data and thus enable effective and efficient communication among healthcare professionals and between patients and providers. SNOMED CT is important for communication because it serves as a semantic foundation for the meaning expressed in a message. Hence, SNOMED CT can ensure consistent and accurate representation of the information communicated, and support correct interpretation of the clinical information within a message.

Communicating clinical data through messages support a range of purposes, including:

• Delivering accurate, accessible, and actionable health information that is targeted or tailored.

• Facilitating the meaningful use and exchange of health information among healthcare professionals.

• Supporting shared decision-making between patients and providers.

• Providing personalized self-management tools and resources.

• Building social support networks.

• Increasing health literacy skills.

Healthcare messages include fields that can be populated with codes from clinical coding schemes. SNOMED CT provides concept identifiers as a means of encoding concepts. These concept identifiers are suitable for use in appropriate fields of many clinical messages.

Implementations of clinical messaging typically constrain the range of values that can be applied to particular fields several reasons for this are listed in the following table.

Table: Reasons for constraining the content of fields in clinical messages

For a more detailed use case example, please refer to the following section:

Communication specifications define structures designed to meet particular requirements. For example, recording a decision to prescribe a particular pharmaceutical product or substance might trigger an electronic prescription sent to the pharmacy. Reference sets may also be used to specify the allowed values in messages and for constraining the codable elements in data entry models. For some bindings it may be relevant to apply certain conditions, to enable that one value set is displayed given a specified criteria, and another value set is displayed given another criteria (or set of criterions). An example of such conditional value set binding is illustrated below.

Table: Types of Reference Sets applicable for messages

The main benefits of using an EHR accrue with the implementation of effective retrieval, analysis and reuse of clinical information. Analysis of health record data may cover:

• Individual patient records to search for significant patterns that may prompt interventions

• Patient groups or cohorts, based on demographics, diagnoses, treatments or interventions

• Enterprise groups, based on teams, wards, clinics, institutions or providers

• Geographical groups, based on a local area, town, region or country

SNOMED CT has a number of unique features, which makes it capable of supporting a range of retrieval and analytics functions, which use reference sets. Examples include, but are not limited to:

• Simple reference sets can be used to represent subsets of SNOMED CT concepts which can be used in queries to identify clinical records

• Simple reference sets can be used to represent non-standard aggregations of concepts for specific use cases

• Simple map reference sets, complex and extended map reference sets can be used to define maps from other code systems to SNOMED CT so that clinical data can be prepared for analytics, and then performed using SNOMED CT

The document provides detailed information about how SNOMED CT can be used for analytics.

For more detailed use cases, please refer to the following examples:

Clinical information recorded using SNOMED CT may include data that is relevant to reports, statistical returns, billing claims, etc. that need to be encoded using a specific code system or a statistical classification such as ICD-10. Mapping allows relevant information to be used for those purposes, minimizing the requirement for additional manual data entry.

Maps are represented as reference sets, which are either of type simple, complex and extended map reference sets. Special cases may also occur, which require a customized reference set to represent the map. An example of this is the 705110001 | LOINC Term to Expression reference set| , which is used to link LOINC Terms to SNOMED CT expressions. The standard reference set format do not support maps to SNOMED CT expressions. Hence, the type of map reference set to use depends on the features that need to be supported by the map.

Simple map reference sets support mapping SNOMED CT codes to a single code or a combination of codes in a target code system. However simple maps are usually only appropriate where there is an equivalent map between SNOMED CT and the values in the other code system.

Complex and extended map reference sets enable the representation of:

• Maps from a single SNOMED CT concept to a combination of codes (rather than a single code) in the target scheme

• Maps from a single SNOMED CT concept to choice of codes in the target scheme. In this case, the resolution of the choices may involve:

  • Manual selection supported by advisory notes

  • Automated selection based on rules that test other relevant characteristics in the source data (e.g. age and sex of the subject, presence or absence of co-existing conditions, etc.)

The completeness of mapping between two code systems depends on the scope, level of detail provided by the two code systems and the precision of mapping required to safely meet the intended mapping use case.

The figure below shows an except of some of the reference sets for maps between SNOMED CT and other code systems, which are available with the International Edition of SNOMED CT. However, local maps may also be developed and applied as part of an Extension to SNOMED CT.

Both extensionally and intensionally defined subsets of SNOMED CT components are useful for specifying clinical queries. For example, subsets of SNOMED CT concepts can be used to categorize patient data by testing for membership in a predefined subset, which is represented as a reference set.

The (ECL) enables simple queries over SNOMED CT content to be expressed. While the language itself does not support querying over the full EHR content, the ECL could be embedded within record-based query languages (such as SQL) to represent the terminological aspects of these queries.

Related to reference sets, the ECL includes the ability to refer to a set of concepts that are referenced by members of a reference set. Additionally, it includes a range of features, such as refinements, disjunction, and conjunction, which support specialized queries. The memberOf function evaluates to the set of concepts that are referenced by the given reference set. For example, the following expression constraint is satisfied by the set of concepts which are members of 649999999104 | Example problem list simple reference set| :

• memberOf 649999999104 | Example problem list simple reference set|

The diagram below illustrates how reference sets can be for specifying queries.

Subsets of SNOMED CT concepts can be used to categorize patient data by testing for membership in a predefined subset. The diagram below illustrates the use of a simple reference set which includes references to rare disease concepts. SNOMED CT does not currently have a defined mechanism to distinguish rare diseases, so this simple reference set is defined extensionally (i.e. by enumeration). This simple reference set is used to create a cohort, by categorizing patients according to their SNOMED CT encoded records, and specific values of contextual metadata. By comparing the patient diagnosis with the concepts included in the reference set it is possible to count the total number of patients who suffer from rare diseases.

A combination of reference sets and subsumption testing can be used to enable a simple, yet sophisticated, analytics feature. For example, you may want to include all of the descendants of reference set members in a particular analysis.

The diagram below illustrate the difference of categorizing patients using two approaches:

1. A subset of components.

   • Two patients are included in a query which analyzes encoded health records and checks for membership in the appropriate subset. E.g. patients with a finding included in the rare diseases reference set.

2. A subset of components and subsumption testing.

   • Three patients are included in a query which test the codes recorded in patient records and check for membership in the appropriate subset or descendants of the subset members. E.g. patients with an associated finding that is referenced in the rare diseases reference set, or any subtypes of the concepts in the reference set.

Managing the components used to represent the large number of clinical data entries in EHRs is an important part of the work related to maintaining the integrity and accessibility of health information. Like SNOMED CT components, reference sets are supported by a robust versioning mechanism that allows historically consistent views of SNOMED CT components and derivatives. This allows reference sets to be used to specify changes in use of concepts and descriptions in different parts of an EHR.

For more detailed use cases, please refer to the following examples:

Constrain Value Sets

Most health records are designed and developed using one or more information models, which describe the information that is collected, stored, communicated and displayed. Some information models are designed for a specific proprietary system, while others are based on a common health information standard. Irrespective of the purpose, design and representation of the information models, the use of clinical terminology is an important part of making the models complete, meaningful and useful. Hence, a consistent approach to the interface between structural elements and terminological representations of information is required to support reliable interpretation of the meaning. Subsets of SNOMED CT components can function as value sets for any health-related information model to enable well-defined, unambiguous models of meaning.

As shown in the diagram below simple reference sets can be used to represent the subsets of SNOMED CT components to be populated as value sets within the relevant information models.

Managing Value Sets

EHR systems will typically utilize a range of different value sets to be used in different places of the system. Representing these value sets using the same terminology will support the comparison of data captured in different contexts. Additionally, using SNOMED CT to represent items value sets instead of locally defined terms enables effective management and overview of information, and helps to mitigate challenges related to redundancy and ambiguity.

Simple reference sets can be used to represent extensionally defined subsets of SNOMED CT components, whereas the query specification reference set are useful for representing the intensional definition of SNOMED CT subsets. In the query specification reference set, the expression constraints can be used to represent the query used for defining the set. This means that the query specification reference set can be used to manage the intensional definition of SNOMED CT subsets that function as value sets, which is illustrated below.

When a component that is a member of a reference set is inactivated, the person maintaining the reference set needs to decide whether a change is required. This depends on the intended use of the reference set being maintained. In the case of a reference set that is being used to constrain data entry, inactive concepts need to be removed from the reference set or replaced by an appropriate active concept. In other reference sets it may be permissible, or even required, to retain an inactive concept in a reference set (for example if a reference set is used in the criteria for a report which may be applied to historical data).

The following figure and subsequent description introduce the overall process for identifying inactive components and using released reference sets to determine reasons for inactivation and potential replacements.

1. One approach to identify the components that have been inactivated since the last release, is to compare snapshot of previous release with current delta release.

2. The reasons for inactivation can be looked up in the 900000000000480006 | Attribute value type reference set| for the particular component type, for example the 900000000000489007 | Concept inactivation indicator attribute value reference set| . The reason is represented by the value of the valueId attribute. For further information, see .

3. The possible replacements for the components that have been inactivated can be determined in the appropriate 900000000000522004 | Historical association reference set|

In the International Edition of SNOMED CT three reference sets of the type 900000000000480006 | Attribute value type reference set| are used to indicate the reason why components have been inactivated. These are:

• 900000000000489007 | Concept inactivation indicator attribute value reference set (foundation metadata concept)|

• 900000000000490003 | Description inactivation indicator attribute value reference set (foundation metadata concept)|

• 900000000000547002 | Relationship inactivation indicator attribute value reference set (foundation metadata concept)|

For example, if the inactivated component is marked as 900000000000484002 | Ambiguous| , this will typically mean that there will be more than one component replacing the inactivated component. The possible replacements will be available in the 900000000000523009 | POSSIBLY EQUIVALENT TO association reference set (foundation metadata concept)| .

Another example is concepts that are inactivated because they were 900000000000482003 | Duplicate| . This is used if two concepts represent the same meaning, because then one of those concepts must be inactivated. The equivalent concept will be represented in the 900000000000527005 | SAME AS association reference set (foundation metadata concept)| . Please refer to to see which reference sets relate to the various reasons for inactivation.

When a new version of SNOMED CT is released this may include changes to the content of the terminology. Components may have been added, inactivated or changed as described in . As part of the terminology maintenance process, it may be appropriate to evaluate both the and to determine appropriate alternatives.

The International Edition of SNOMED CT distributes a set of reference sets that record the reason that each inactive component was inactivated. These are referred to as "historical association" reference sets. There is one historical association reference set for each type of historical association as shown in the table below.

Table: Association reference set types in the International Release of SNOMED CT

The following table holds example entries for the 900000000000526001 | Replaced by| reference set. With this reference set is possible to automatically identify that the inactive concept 696005 | Chronobiologic disorder| should be replaced with the concept 387605007 | Abnormal chronobiologic state| . This type of reference set is particularly useful for ensuring consistent use of SNOMED CT over time. The reference set mechanism here provides an easy and standardized way of managing changes to coding or documentation practice over time.

Table: Sample content from 900000000000526001 | REPLACED BY association reference set |

Many clinical applications include data entry interfaces controlled or assisted by protocols, templates or structured data entry forms. Each field on a data entry form may allow only a limited set of terms or concepts to be entered . The set of candidate term or concept may range from very small (e.g. a set of priorities for a procedure) to very large (e.g. any general diagnosis). Reference sets can be used to restrict the possible values that meet the requirements of a particular data entry protocol.

Examples of using reference sets to support search and data entry include:

• can be used to constrain searches or provide values for selection lists.

• can be used to prioritize search results or provide an alternative ordering of search results.

• can be used to supplement search results or data entry options with additional textual or coded information, such as advice on intended usage.

• can be used to ensure that the preferred descriptions, for a given dialect, care setting or clinical context, are displayed.

A SNOMED CT enabled application can use an appropriate reference set to display the valid data entry options and constrain text searches. Below are more detailed use case examples.

In many care settings, similar data sets are collected for each patient. Clinical consultations for many conditions involve repeatable sequences of data entry. These structured and predictable data entry requirements can be met using sets of customized data entry forms designed to collect appropriate data items.

When using a structured data entry mechanism, SNOMED CT encoded data can be selected in a variety of ways. For example, the concepts or descriptions may be selected directly from a list, or the encoding may result from responses to simple choices or the entry of particular values. Simple reference sets can ensure that SNOMED CT codes are entered effectively and consistently.

A simple reference set of concepts may be used to represent the options available in a small selection list. Similarly, a simple reference set of descriptions or a language reference set may specify the set of descriptions available for searching in a specific coded data element. The figure below illustrates how a simple reference set is is used as a value set in a data entry form.

Simple reference sets enable text searches to be constrained to those components relevant to a particular field. The provides additional detail about how to make effective and efficient search capabilities using SNOMED CT. The figure below illustrates the use of a simple reference set to constrain the values returned by a text search in a data entry form. Additionally, dedicated search features support searching the content of the reference set.

Even though subsets are typically used to specify content for inclusion, some situations may require particular components to be excluded from another set. Excluding sets of SNOMED CT components can be used to prevent certain concepts appearing in particular search and data entry items.

Like every subset of SNOMED CT components, it is possible to define the subset for exclusion either intensionally or extensionally . This is illustrated in the figure below. When intensionally defined, a query specification reference set can be used for the intensional definition, and a simple reference set can be used for the expansion of the set.

The criteria for a successful implementation of SNOMED CT includes the customization of SNOMED CT to meet user needs. The order in which SNOMED CT components are displayed is often important for data entry and searching. This topic is further explored in the . In general, rational ordering of selectable items depends on the nature of the application and its operating environment. The table below shows examples of ordering data entry items and search results rationally.

Table: Examples of rational ordering

Displaying items for data entry in a rational way typically involves organizing the values in a selection list in an order that is logical for the end users. As illustrated in the figure below, an ordered reference set can be used to specify the order in which SNOMED CT components should be displayed.

Examples of presenting concepts (or descriptions) in an order that is rational or helpful for a particular purpose include:

• • Displaying numbered body parts, such as fingers, cranial nerves or vertebrae, in numeric order

  • Displaying ordinal values, such as frequencies, severities or stages, from lowest to highest

The table below shows how the order of cranial nerves can be specified in an . The order attribute is used to indicate the sequential order of each subset member.

Some situations may require a set of subset members to be grouped. For example, a set of concepts may need to be grouped based on how frequently they are used within a particular specialty, department or data entry scenario. In this case, an may be used for prioritization, instead of a purely sequential ordering of each member. Prioritization is similar to sequential ordering, but also supports assigning the same rank to multiple components. A common use of prioritization is to support rational ordering of concepts or descriptions for display of data entry items and search results. More advanced uses may also be required, for example where the priority order is used to trigger certain decision support features or data entry options.

can be used to specify and display a customized navigation hierarchy. Alternative hierarchical representations of SNOMED CT can support data entry by satisfying the requirements of a specific use case, and addressing some of the challenges of displaying an unordered polyhierarchy (as defined by SNOMED CT's subtype structure).

The figure below shows the way a navigation hierarchy is represented. The example reference set contains a set of description components used to describe finger structures.

The | All fingers | components is linked to the | Hand |, and the | Thumb | is linked to the | All fingers component | The | Thumb | is placed first because it has the order value 1. Similarly, the components for | Second finger |, | Third finger |, | Fourth finger | and | Fifth finger | are also linked to the | All finger | component in the order specified by the order value. As shown in the figure the direction of the associations goes from the referenceComponentId to the linkedToId, so the components referenced by the linkedToId are used to form the groups specified in the hierarchy

The usability of the for representing alternative hierarchy can be maximized by:

• Constraining the number of levels in the hierarchy and/or the number of concepts at each level.

  • Using many levels, each with a relatively small number of concepts, allows the most common options to be displayed with a higher priority.

  • Using fewer levels, each with a relatively large number of concepts can reduce the number of levels that needs to be navigated to find an appropriate concept.

  • Options that are never (or rarely) used can be excluded from a customized navigation hierarchy to limit the range of choices available.

SNOMED CT represents relationships between concepts that are necessarily (i.e. always) true. However, other relationships between concepts may exist in specific situations or use cases. An can be used to represent these additional relationships, which are not necessarily true, but which are needed for a specific purpose. Examples include:

• Associations between procedures and the clinical findings that serve as an indication for that procedure. These associations enable relevant procedures to be displayed when specific clinical findings are selected.

• Associations between a medication and its known side effects. These associations enable relevant side effects to be displayed when specific medications are selected

• Associations between a disease and the set of possible symptoms that may be experienced. These associations enable relevant diseases to be displayed when a set of symptoms are selected.

Association Reference Set can be used to constrain (or guide) data entry into fields, where the value is dependent on (or has some type of association with) the value of another field. While other technical solutions are possible, the Association Reference Set provides a standardized way of representing and distributing the associations required to support this functionality. The figure below illustrates how an Association Reference Set could be used for this purpose.

The table below illustrates some of the use cases that SNOMED CT reference sets support. Furthermore, it includes some typical example uses for each use case, and presents the types of reference sets relevant to these example. You can click on the diagrams and the text to navigate to the subpage, which provides more information about each of the use cases, examples and reference sets. The examples shown in the table are not exhaustive. Instead, they illustrate some common scenarios for each type of reference set.

Table: Reference set use cases

SNOMED CT is a multinational, multilingual terminology which enables the link between concepts and different linguistic representations. Hence, SNOMED CT has a built-in framework to manage different languages and dialects. Each concept, representing a clinical meaning, can be linked to descriptions, which express that particular meaning using different terms, languages or dialects. This means that descriptions can be added to SNOMED CT concepts and expressed in other languages than what is included in the International Edition. Often these additional descriptions are used in a national Extension of SNOMED CT.

Consequently, one aspect of implementing and customizing SNOMED CT to meet specific user needs is to determine and specify preferences for the descriptions to be used, e.g. for display in an electronic health record or more generally, as preferences within a specific clinical domain or facility.

In the International Edition of SNOMED CT language reference sets are included which specifies the preferred and acceptable synonyms for each concept in both US english and GB english. However, language reference sets can also be developed and applied locally to specify what descriptions are preferred and acceptable in a given context. This means, that even within a single country, or a single hospital, different descriptions can be applied to meet the user preferences, even without relaxing the need for consistency and unambiguous concept definitions.

For more detailed use case examples, please refer to the following sections:

Indications of Acceptability of Descriptions

When SNOMED CT is being used as an interface terminology, the preferred term for each concept should be used as the default for display on the user interface. Each concept may have a different preferred term in different languages, dialects, specialties or care settings, and so these can be configured for a specific clinical environment. Preferred terms and acceptable synonyms are defined in SNOMED CT using a language reference set, which references the subset of descriptions used in a given language, dialect, specialty or care setting. Two language references sets are distributed with the International Edition of SNOMED CT (for US-English and UK-English), and various member countries distribute their own national language reference sets. Additional language reference sets may be created at the regional, specialty, institute or software product level to truly customize the local user’s experience.

The most common use case for language reference sets is to specify the acceptable and preferred terms for use within a particular country or region. As illustrated below, descriptions associated with a single SNOMED CT concept can be specified as a preferred or acceptable synonym.

Using SNOMED CT at the user interface level can be accomplished in various ways using different types of reference sets. Approaches include:

• Using SNOMED CT directly as interface terminology

  • using a of descriptions used for display

  • using a which specifies preferred and acceptable synonyms

• Using a separate interface terminology which is mapped to SNOMED CT

As SNOMED CT descriptions can be used directly as an interface terminology, subsets of SNOMED CT descriptions may be directly shown to a clinician at the user interface . These description subsets may be customized

• for a specific language or dialect (such as Spanish or Australian English)

• for a given clinical specialty (such as cardiology or oncology)

• for a user type (such as a doctor, nurse or patient)

• a care setting (such as an aged care home or a hospital inpatient ward) or

For each of these use cases, the set of acceptable terms and the preferred term for that clinical use can be identified. However, when searching SNOMED CT it is recommended that any term that is considered "acceptable" for use in a given context should be available to support searching for an appropriate concept, while the preferred term is often used to confirm the intended meaning of the selection.

Representing a subset of descriptions can be done using a simple reference set, as illustrated in the diagram below. However, other types of reference set types may be feasible if additional features are required, such as specifying which descriptions are preferred or acceptable (language reference set), ordering or prioritizing the descriptions (ordered reference set), annotating the description with some textual information (annotation reference set) or associating the descriptions to other components (association reference set).

While a simple type reference set can be used for defining a subset of descriptions, a is designed to support indication of language and dialect preferences through the addition of the 'acceptability' attribute. This allows preferred and acceptable descriptions to be defined for any context of use, including within a particular country or region, within a clinical specialty or care setting, within an organization or department, or for a specific type of user.

The table below shows an excerpt from two language reference sets, which are both distributed with the International release of SNOMED CT, i.e. the 900000000000509007 | United States of America English language reference set| and the 900000000000508004 | Great Britain English language reference set| . Both reference sets reference Descriptions available in the Description file in the International Edition.

Table: Excerpt from the | United States of America English language reference set | and the | Great Britain English language reference set |, which are both distributed with the International release of SNOMED CT.

The diagram below illustrate the use of language reference sets and show the relation between the language reference set and the description file. Even though three descriptions are specified for the same concept in the description file, the language reference set specifies which of these descriptions are preferred and acceptable within a given language, dialect or organization. If a description is not referenced in the language reference set, then that particular description can be regarded as not acceptable within the context where the language reference set apply.

The benefits of directly using the terms from SNOMED CT on the user interface are that

• no mapping is required from the clinical phrases to the clinical meanings. The design of SNOMED CT already include human-readable representations of concepts

• the clinical intent of a selection can be confirmed if required using other terms linked to the same concept (such as the ‘Preferred Term’)

• the equivalence of the terms to the clinical meaning is ensured by using quality authoring processes

• the higher quality of SNOMED CT coding can consequently lead to higher quality analytics results

• This approach may require a transition of the user experience. However, it should be noted that new descriptions may be added to SNOMED CT to meet the expectations of the users.

• Subsets need to be created and maintained to support users in searching for and recording the appropriate SNOMED CT concepts.

An implementer who is motivated to introduce SNOMED CT records, but who is also keen to keep using an existing interface terminology, may choose to map between the interface terminology and SNOMED CT to enable that SNOMED CT is used for storage. Using this approach each item in the interface terminology is bound (or mapped) to an appropriate SNOMED CT concept. When the interface term is selected, the identifier of the bound SNOMED CT concept is stored in the record. It is important when an interface terminology is being used that the mapping to SNOMED CT is of sufficient quality (ideally equivalent) to support the use cases for which the data will be used. Using an interface terminology, for example, may be useful for structured data entry, where only part of the meaning is represented by the selected term, and the rest by the surrounding interface context. A simple map reference set can be used to represent the map between the interface terminology and SNOMED CT, in the case where there are a 1:1 map between each term in the interface terminology and SNOMED CT concepts.

Linking SNOMED CT components to knowledge resources (such as clinical guidelines or decision support systems) is a way of adding significant value to electronic health records.

The diagram below illustrates the range of use cases for knowledge linkage including presenting alerts to the user, displaying relevant clinical guidelines and treatment protocols, or automatically populating an order, message or report.

Reference sets can be used to enable knowledge linkage in different ways. Examples include but are not limited to:

• Annotation reference sets can be used to add a linkage between a referenced component and a string-representation of a specific knowledge resources.