4.2.1.0 Using SNOMED CT with FHIR

Note that this page has been copied from http://build.fhir.org/snomedct.html purely for the purpose of review and consolidating feedback. It would be acceptable to modify this document however, so we have a 'complete' draft to return to HL7. We'll be able to track the changes through Confluence document history.

Vocabulary

Work Group

Maturity Level: 5

Ballot Status: Trial Use

4.2.1.0.1 Summary

Source	SNOMED CT is used in FHIR international standards and resources. SNOMED CT is owned, maintained and distributed by SNOMED International . SNOMED International is the organization which publishes the International Edition of SNOMED CT. SNOMED International Members may also distribute their own SNOMED CT National Edition, which contains the international release plus local extension content and derivatives.
System	The URI http://snomed.info/sct identifies the SNOMED CT code system.
Version	Where a code system version is used, it should be specified as a URI that represents a specific SNOMED CT Edition published on a particular date (e.g. the International Edition or a National Edition, with a version date), following the SNOMED CT URI Specification (see note below)
Code	The following SNOMED CT artifacts are valid in the code element for the http://snomed.info/sct namespace: Concept IDs and SNOMED CT Expressions (using SNOMED CT Compositional Grammar). SNOMED CT Terms and Description Identifiers are not valid as codes in FHIR, nor are other alternative identifiers associated with SNOMED CT Concepts. Note: when SNOMED CT terms must be exchanged, use the Description Id Extension.
Display	The correct display for a SNOMED CT concept is one of the terms associated with that concept. The best display is the preferred term in the relevant language or dialect, as specified in the associated language reference set. SNOMED CT synonyms may be case sensitive. SNOMED International does not define terms for expressions. If a SNOMED terminology producer publishes human-readable terms for expressions in an expression repository, this term may be used as the display. Similarly, if a SNOMED terminology producer publishes an official template for generating terms from an expression, a term generated using the template may be used as the display. If no term or description template has been published, the full expression with terms embedded may be used. Note that Display is not intended to contain terms entered by the user that have not been officially published by a SNOMED CT Terminology Producer.
Inactive	Inactive codes are identified using the 'inactive' property (see below).
Subsumption	SNOMED CT Subsumption testing for concepts is based on the \|is a\| relationship defined by SNOMED CT.
Filter Properties	Several filter properties are defined, as described below.

This specification publishes a canonical SNOMED CT code system resource. See also the SNOMED CT Usage Summary.

Note: The SNOMED International glossary

explains some of these SNOMED CT specific terms.

4.2.1.0.2 Versions

There is no single distribution that contains all defined SNOMED CT codes in all contexts of use. Instead the International Edition contains all concepts shared and agreed to be internationally relevant and each National Release Centre distributes this International Edition plus additional national content (to extend the international set). Other release authorities may also be designated. The SNOMED CT URI Specification

describes how to unambiguously reference a particular version of a SNOMED CT edition:

http://snomed.info/sct/[sctid]/version/[YYYYMMDD]

where [sctid] is the concept id that identifies the given SNOMED CT edition (based on the identifier of the most dependent module), and "YYYYMMDD" is the date of release. Examples of sctids that identify a specific edition are listed here.

4.2.1.0.3 SNOMED CT Expressions

A SNOMED CT Expression is a structured combination of one or more clinical concepts, stated using Compositional Grammar Syntax.

Expressions may optionally contain display terms.

4.2.1.0.4 Copyright and Licenses

Note that many implementations are in the habit of simply using the date of release in the form YYYYMMDD (e.g. "20140531"), and assuming that the edition is known. However this is not always safe, so implementations that populate the version element must use the URI form.

This specification includes content from SNOMED Clinical Terms® (SNOMED CT®) which is copyright of the International Health Terminology Standards Development Organisation (IHTSDO). Implementers of these specifications must have the appropriate SNOMED CT Affiliate license - for more information contact http://www.snomed.org/snomed-ct/get-snomed-ct

or info@snomed.org.

4.2.1.0.5 RDF

The SNOMED International URI specifications use the namespace http://snomed.info/sct for the code system, and the URI http://snomed.info/id for the individual concepts in the code system. This means that when a SNOMED CT concept is converted from the system::code pair, where the system is http://snomed.info/sct, to the RDF ontological form, the representation is http://snomed.info/id/[concept-id]. Expressions are represented using the URI pattern http://snomed.info/scg/[expression]. Expressions represented in this way SHALL not contain whitespace, terms, or comments.

4.2.1.0.6 SNOMED CT Properties

In addition to the standard properties, the following properties are defined for SNOMED CT:

Property Name	Data Type	Comments
inactive	boolean	Whether the code is active or not (defaults to false). This is derived from the active column in the Concept file of the RF2 Distribution (by inverting the value)
sufficientlyDefined	boolean	True if the description logic definition of the concept includes sufficient conditions. This is derived from the definitionStatusId value in the Concept file of the RF2 distribution (i.e. If 900000000000073002 \|Sufficiently defined concept definition status\| then true).
moduleId	code	The SNOMED CT concept id of the module that the concept belongs to.
normalForm	string	Generated Necessary Normal form expression for the provided code or expression, with terms. See http://snomed.org/nnf
normalFormTerse	string	Generated Necessary Normal form expression for the provided code or expression, conceptIds only.

SNOMED CT relationships, where the relationship type is subsumed by 410662002 |Concept model attribute|, also automatically become properties. Properties that represent SNOMED CT concept model attributes are referred to using their concept id, rather than their human readable term.

For example, the laterality property is represented using the concept id '272741003', rather than the term 'laterality':

Property Name

Data Type

Comments

272741003

code

The value of the laterality attribute in the definition of the given code or expression.

The equivalent URI for the Laterality property is http://snomed.info/id/272741003 (see the code system definition).

Note that when a $lookup operation is performed on a SNOMED CT concept, servers SHALL return the full URI for the edition and version being used (see above) in the version property. Other properties are at the discretion of the server and the client.

4.2.1.0.7 SNOMED CT Filters

This section documents the property filters that can be used with the SNOMED CT code system in value set composition statements.