SNOMED CT HL7 IPS Free Set

In 2019, SNOMED International and HL7 International announced the formalization of a license agreement in which a relevant "Free for Use" Set of SNOMED CT coded concepts will be used within the HL7 International Patient Summary (HL7 IPS). HL7 is a not-for-profit, ANSI-accredited standard developing organization dedicated to providing a comprehensive framework and related standards for the exchange, integration, sharing, and retrieval of electronic health information that supports clinical practice and the management, delivery, and evaluation of health services. The HL7 IPS is a minimal and non-exhaustive patient summary dataset, specialty-agnostic, and condition-independent, but readily usable by clinicians for the cross-border unscheduled care of a patient. The collaboration is consistent with the aims of both organizations to support international harmonization. 

The SNOMED CT International Patient Summary (IPS) is international in scope and in addition to harmonization with HL7 IPS, is aligned with CEN's European Standard for the Patient Summary. The IPS free set consists of more than 8,000 SNOMED CT terms for use in implementations of the HL7 CDA R2 and FHIR IPS Implementation Guides worldwide. The SNOMED CT HL7 IPS free set contains concepts that can record the following data:

• General information about the patient (e.g., gender)
• Medical summary of most important clinical data (e.g., allergies, current medical problems, major surgical procedures)
• A list of current medications

The HL7 IPS Free Set is available for non-affiliates directly from HL7, and as part of the Global Patient Set a package that collects different free sets released by SNOMED International,  these releases consists of a list of concept identifiers, fully specified names, preferred terms (in international English) and active/inactive status flags. The HL7 IPS Free Set is designed to support data sharing. However, it lacks the additional capabilities of the SNOMED CT terminology, which is available via a full SNOMED CT release. The HL7 IPS Free Set is also available for Members and Affiliates as a reference set, distributed in a RF2 release package via a National Release Center or the international MLDS service. This reference set is maintained and updated annually, in line with the July SNOMED CT International Release. For more information, please contact info@snomed.org.

IPS Terminology

SNOMED International's IPS Terminology represents an evolution of the HL7 IPS Free Set, providing advanced terminology features for non-affiliates to use in their IPS solutions. In particular, it adds a hierarchy, defining relationships and extra synonyms from the SNOMED CT international edition, to form a sub-ontology of SNOMED CT. A sub-ontology is a functional set of concepts and relationships extracted from the full SNOMED CT ontology that provides the following features:

• It can be loaded in a SNOMED CT compatible terminology server
• It includes all the active concepts from the HL7 IPS Free Set
• The concepts are organized into the same hierarchies as the SNOMED CT International Edition (e.g., Clinical Findings, Procedures)
• The content is expanded to include a minimal set of additional grouper concepts
• The content also includes (inferred) relationships that define the meaning of the included concepts
• The US-English and GB-English language reference sets are included just like in the complete International Edition
• ECL (Expression Constraint Language) queries can be executed over the IPS Terminology to support value set definitions and simple data analytics

Please note that the IPS Terminology contains only a subset of the full international release of SNOMED CT, and therefore the features above are limited to this restricted content.

The IPS Terminology is made available as an RF2 package with a similar format to other SNOMED CT releases. However, the package is not fully RF2 compatible, the content is available only in "snapshot" format (i.e. the current state of each component), and it includes only components that are active at the time the terminology is extracted. The relationship ids are published using temporary ids. Each IPS Terminology release replaces the previous one, providing a new snapshot of active content; it's not designed for incremental updates.

The IPS Terminology package does not include historical information (which is normally available to licensed Affiliates in full SNOMED CT releases).

The IPS Terminology package can be loaded into SNOMED International's Snowstorm, a freely available, open-source terminology server maintained by SNOMED International. SNOMED International provides a browser for the IPS Terminology.

Feature Comparison

The IPS Terminology is a subset of the SNOMED CT International Edition. It is designed to provide the necessary terminology features for a simple IPS implementation. It has more features than the IPS Free Set, but less than a complete SNOMED CT edition. A complete SNOMED CT edition provides advanced features to improve the capabilities of an implementation.

The table below provides a high-level comparison of the key features of each type of terminology resource.

Example of Use

The HL7 FHIR IPS Implementation guide specifies the terminology binding for each of the coded data elements within the IPS composition. For example, the Procedures-IPS value set defines the valid values for the 'code' data element in the Procedures resource. The Procedures-IPS value set is defined using a logical definition, consisting of the following inclusion and exclusion clauses.

• Include codes from http://snomed.info/sct where concept descends from 71388002 (Procedure)
• Exclude codes from http://snomed.info/sct where concept is-a 14734007 (Administrative procedure)
• Exclude codes from http://snomed.info/sct where concept is-a 59524001 (Blood bank procedure)
• Exclude codes from http://snomed.info/sct where concept is-a 389067005 (Community health procedure (procedure))
• Exclude codes from http://snomed.info/sct where concept is-a 442006003 (Determination of information related to transfusion)
• Exclude codes from http://snomed.info/sct where concept is-a 225288009 (Environmental care procedure)
• Exclude codes from http://snomed.info/sct where concept is-a 308335008 (Patient encounter procedure)
• Exclude codes from http://snomed.info/sct where concept is-a 710135002 (Promotion (procedure))
• Exclude codes from http://snomed.info/sct where concept is-a 389084004 (Staff related procedure (procedure))

This logical definition is equivalent to the following SNOMED CT Expression Constraint (ECL) query, which can be executed against any full edition of SNOMED CT to extract the list of concepts to include in this value set.

When using the IPS Terminology for recording and sharing IPS data, it may be necessary to simplify these terminology bindings to ensure that only codes included in the IPS Terminology are referenced by the ECL query. For this example, the following query (which refers only to concepts contained in the IPS Terminology) can be used to extract the list of IPS Terminology concepts to include in this value set.

This ECL expression can be submitted to a terminology server (on which the IPS Terminology has been installed), via a standard HL7 FHIR Terminology Services API, to extract the SNOMED CT concepts that may be used in the Procedures-IPS value set. This capability is available in all standard SNOMED CT Releases, but it was not previously possible with the HL7 IPS Free Set. However, this has been enabled by the new features of the IPS Terminology. Using ECL expressions in this way, implementers can update their value sets with each new release of the IPS Terminology.