1. Introduction

SNOMED CT terminology provides a common language that enables a consistent way of indexing, storing, retrieving, and aggregating clinical data across specialties and sites of care. The SNOMED CT US Edition is a combination of the full January 2024 SNOMED CT International Edition and the US Extension of SNOMED CT.

The International Health Terminology Standards Development Organisation (IHTSDO^®), trading as SNOMED International, maintains the SNOMED CT technical design, the content architecture, the SNOMED CT content (includes the concepts table, the descriptions table, the relationships table, a history table, and ICD mappings), and related technical documentation. The SNOMED CT US Edition is developed and maintained by the United States National Library of Medicine and is available to authorized Unified Medical Language System (UMLS) Metathesaurus Licensees. This material includes SNOMED CT which is used by permission of the IHTSDO. All rights reserved.

SNOMED CT was originally created by the College of American Pathologists. "SNOMED" and "SNOMED CT" are registered trademarks of IHTSDO. You must have a UMLS Metathesaurus license to access SNOMED CT US Edition data files. License information is available from NLM (https://www.nlm.nih.gov/healthit/snomedct/snomed_licensing.html). 

1.1. Background

This document provides a summarized description of the content changes included in the March 2024 release of the SNOMED Clinical Terms® US Edition.

It also includes technical notes detailing the known issues which have been identified. These are content or technical issues where the root cause is understood, and the fix has been discussed and agreed, but has yet to be implemented.

This document is available as a web resource as well as alongside the March 2024 US Edition release (https://www.nlm.nih.gov/healthit/snomedct/us_edition.html). 

1.2. Scope

This document is written for the purpose described above and is not intended to provide details of the technical specifications for SNOMED CT or encompass every change made during the release. These Release Notes should be used in combination with the SNOMED CT January 2024 International Edition Release notes. 

2. Content Development Activity 

2.1. Summary

The March 2024 SNOMED CT US Edition marks the thirteenth release with content authoring tooling and release production provided by SNOMED International Managed Service. Quality assurance of the release was completed by both NLM and SNOMED International. Additionally, in October 2017, NLM sunset the United States SNOMED CT Content Request System and migrated to the SNOMED International hosted and maintained US CRS (https://us-request.ihtsdotools.org). 

2.1.1. March 2024 US Edition of SNOMED CT Statistics 

These statistics include the active content from the January 2024 International Edition and the March 2024 US Edition.

These statistics include the content from the March 2024 US Extension.

2.2.  Quality Initiative

The Quality Initiative (QI) project is the implementation of the Quality Strategy. After a successful pilot project for the July 2018 release the next stage has been implemented for subsequent releases including January 2024.

Quality improvement tasks are being deployed to improve internal structural consistency and ensure compliance with editorial policy related to the stated modeling of content. Additionally, correction or addition of defining relationships is being carried out to accurately reflect current clinical knowledge and ensure the semantic reliability of descriptions associated with a concept. 

To see the QI improvement tasks from the January 2024 International Edition, please see the January 2024 International Edition release notes.

The following QI tasks have been undertaken and/or completed in the US Extension:

2.2.1. Disorder combination modeling update

Clinical Finding and Disorder concepts that contain a causal relationship represented in the fully specified name (FSN) have been remodeled to align with current editorial policy. In cases where the causation is physical object or force, organism, or substance, the FSN should be represented as <x> caused by <y>. When causation is another finding or disorder, an event, or procedure then the FSN should be represented as <x> due to <y>.

2.2.2. Remove articles (i.e. a, an, the) from descriptions

Per SNOMED Editorial policy, descriptions should not include the articles such as a, an, and the. A review of concepts in the US extension was completed. Descriptions containing articles were inactivated and new descriptions added to concepts to remove articles.

2.2.3. Proximal and intermediate proximal Primitive modeling

Concepts modeled with a sufficiently defined IS A parent concept have been reviewed and modeling updates implemented to transition as many of these concepts to proximal or intermediate proximal primitive model as possible. 

2.2.4. Microbiology Project Group work

Work continues by SNOMED International to promote concepts from the 415671008 |Domain Eukarya (organism)| hierarchy from the four participating national extensions. Additionally, updates continue to be applied to the Bacteria domain to align it with LPSN.

2.3. SNOMED CT derived products 

2.3.1. SNOMED CT to ICD-10-CM map 

The purpose of the SNOMED CT to ICD-10-CM map is to support semi-automated generation of ICD-10-CM codes from clinical data encoded in SNOMED CT for reimbursement and statistical purposes. All current pre-coordinated SNOMED CT concepts from the US Edition (US Extension + International release) within three hierarchies, (Clinical findings, Events, and Situations with Explicit Context) are potentially in scope for mapping to ICD-10-CM. 

The SNOMED CT to ICD-10-CM map is released in RF2 format within the US Edition, as well as a standalone download (https://www.nlm.nih.gov/research/umls/mapping_projects/snomedct_to_icd10cm.html). The map is also available in a human readable format (tls_Icd10cmHumanReadableMap_US1000124_YYYYMMDD.tsv) contained within a standalone download - SNOMED_CT_to_ICD-10-CM_Resources_YYYYMMDD.zip.

The SNOMED CT to ICD-10-CM map is released as Refset 6011000124106 | ICD-10-CM extended map reference set (foundation metadata concept)|. The map data are in the file xder2_iisssccRefset_ExtendedMapSnapshot_US1000124_YYYYMMDD.txt, which is in the Map folder under Refset in the Snapshot Release Type folder. 

PLEASE NOTE: Starting with the 2019 September SNOMED CT US Edition (20190301) release, the SNOMED CT to ICD-10-CM map refset data will be maintained as per the SNOMED CT RF2 specifications. 

Additional map refset information can be found in the SNOMED CT to ICD-10-CM Release Notes (doc_Icd10cmMapReleaseNotes_Current-en-US_US1000124_YYYYMMDD.pdf) found in the standalone download or online. Technical information (doc_Icd10cmMapTechnicalSpecifications_Current-en-US_US1000124_YYYYMMDD.pdf) for the map can also be found in the standalone download. 

On September 26, 2019, an updated version of the map (6011000124106 | ICD-10-CM complex map reference set (foundation metadata concept)| ) was released. This updated version included an appending of the previously released mapping refset data, originally pulled from the 20190301 release. The newly released version, which includes all of the previously released data, now includes 260,749 mapped records. This is now considered the baseline for the SNOMED CT to ICD-10-CM map. 

2.3.2. Route of administration

The NLM maintained Route of administration reference set (442311000124105 | Route of administration reference set) is located in the file der2_Refset_Simple(Snapshot, Delta, Full)_US1000124_YYYYMMDD.txt, which is in the Content folder under Refset, in each of the three RF2 Release Type folders. The refset contains a set of terms related to the location of administration for clinical therapeutics. The purpose of the Route of Administration refset is to define a portion of which can be used in the Drug Listing section of Structured Product Labeling (SPL), or for documentation and encoding of clinical information regarding substance administrations. Only concepts that are subtypes of the concept 284009009 | Route of administration value (qualifier value) are included in the refset. Please note the 442311000124105 | Route of administration reference set has been in static status since 2014 September US Edition release (20140901) and was deprecated from the US Edition release package as of the September 2023 US Edition release onwards.

The concept "442311000124105 |Route of administration reference set (foundation metadata concept)|" + relates components (including the refsetDescriptor record) remains active, however all 144 records that comprise this refset are inactivated in the SimpleRefset file: der2_Refset_SimpleSnapshot_US1000124_20230901.txt

In order to preserve the historical audit trail within the US Edition release package, the records have been inactivated (set the "active=0") rather than being deleted from the package completely.

The Route of Administration concepts are maintained as an intensional value set in the NLM Value Set Authority Center (VSAC) (https://vsac.nlm.nih.gov/valueset/2.16.840.1.113762.1.4.1018.98/expansion). Users are required to have a UMLS account to access VSAC. If you don't have a UMLS account, you can request one here: https://uts.nlm.nih.gov/uts/signup-login

2.3.3. Transitive closure file

NLM provides a transitive closure script and generated transitive closure table within the SNOMED CT US Edition release. The transitive closure is the complete set of relationships between every concept and each of its super-type concepts (parents and ancestors). The transitive closure files can be used to support SQL queries when created and stored as a table in a relational database. If applied in a full release, it will contain the full history and allow for subsumption queries to be applied based on any release. The NLM transitive closure script provides a comprehensive view of all of the supertype ancestors of a concept derived by traversing all the 116680003 | is a | relationships between that concept and the root concept. The transitive closure table represents the transitive closure of the 116680003 | is a | relationships of all active concepts. NLM provides the transitive closure table in the US Edition release to provide support for easier implementation and a reference against which to check alternative algorithms. 

As of the September 2020 release, the Transitive Closure script, tls2_TranstiveClosure_US1000124_YYYYMMDD.pl, and the Transitive Closure table res2_TransitiveClosure_US1000124_YYYYMMDD.txt, are located in a separate bundled zip file (SnomedCT_TransitiveClosureResourcesRF2_PRODUCTION_YYYYMMDDT120000Z.zip) on the NLM US Edition page. For the table, the superTypeId is the id of the concept playing the supertype role, set to an Identifier of a concept. The subTypeId - Id of the concept playing the subtype role. Set to an Identifier of a concept. 

3. Technical Notes

3.1. Known Issues

Known Issues are content or technical issues where the root cause is understood, and the resolution has been discussed and agreed but has yet to be implemented. This can be due to a number of reasons, from lack of capacity within the current editing cycle, to the risk of impact to the stability of SNOMED CT if the fix were to be deployed at that stage in the Product lifecycle.

In addition to the Known Issues reported by the IHTSDO for SNOMED CT International Edition (SNOMED CT January 2024 International Edition Release notes), the following are Known Issues for the SNOMED CT March 2024 US Edition that have been identified and will be resolved in the next editing and production cycle: 

3.2. Resolved Issues

Resolved issues are Known Issues which were not fixed as part of the previous release lifecycle, but which have now been resolved for this March 2023 US Edition. These can be issues found during the Pre-Production or Production phases of the testing of the current release, which were resolved before the final deployment of the final production release. Finally these can be issues which were reported or found during the testing phase, but which have been closed without any action taken. 

In addition to the Resolved Issues reported by the IHTSDO for SNOMED CT International Edition (SNOMED CT January 2024 International Edition Release notes), the following Resolved Issues for the SNOMED CT March 2024 US Edition:

3.3. Technical Updates

In addition to the Technical Updates reported in the following monthly Release Notes:

• • https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+July+2023+International+Edition+-+SNOMED+International+Release+notes
  • https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+September+2023+International+Edition+-+SNOMED+International+Release+notes
  • https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+October+2023+International+Edition+-+SNOMED+International+Release+notes
  • https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+November+2023+International+Edition+-+SNOMED+International+Release+notes
  • https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+December+2023+International+Edition+-+SNOMED+International+Release+notes
  • https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+January+2024+International+Edition+-+SNOMED+International+Release+notes

...the following technical updates pertain to the US Edition: 

3.3.1. Changes to the International Edition Release Schedule

As you may already know SNOMED International have transitioned to a monthly delivery schedule for the International Edition of SNOMED CT. The move realizes several benefits, including:

• The potential to be able to get content changes into the terminology in a shorter time frame.
• The fostering of better interoperability, as a result of entities being able to consume release content that is more aligned with other organizations.
• The prevention of circular dependencies that occur in longer projects, due to the move towards smaller, more manageable authoring projects.
• More automated validation services, as a result of the inherent removal of the Alpha/Beta stages in the Release cycle.

Whilst most users will continue unaffected (as they can simply continue to download the releases every 6 months as always), this transition necessarily involved a few changes to process/packages:

• Delta files have been removed from both International and Managed Service release packages, including the US Edition. A Delta Generation service will be provided for those who need it. The Delta Generation Tool allows users to create their own Delta between two fixed release dates - you can find it here:
  • https://github.com/IHTSDO/delta-generator-tool/releases
• There is no longer any need to separate the Map files from the International Edition - the ICD-0/ICD-10 Maps will continue to be published in each Monthly International Edition release package (in line with that month's content) for the foreseeable future, unless we experience issues with the new process in Production, and they need to be removed at a later date.
• The first monthly Release of the SNOMED CT International Edition was the 28th February 2022, however the Delta files were removed from the International Edition from the January 2022 Release, and from the US Edition from the March 2022 Release onwards.

Please note - While the SNOMED CT International Edition has moved to monthly releases, the US Edition of SNOMED CT will remain on the current bi-annual release schedule of March and September.

3.3.2. RF2 package naming conventions

3.3.2.1. US Edition package naming convention

Please be aware that as of the March 2023 Release of the US Edition onwards, the RF2 package naming convention has been changed in order to bring it in line with the naming standards across all Managed Service products. This is being changed from:

• • SnomedCT_USEditionRF2_PRODUCTION_[date]T[time]Z.zip

...to the following:

• • SnomedCT_ManagedServiceUS_PRODUCTION_US1000124_[date]T[time]Z.zip

So, for the March 2023 Release of the US Edition, for example, the RF2 package would have originally been called:

• • SnomedCT_USEditionRF2_PRODUCTION_20230301T120000Z.zip

...whereas from now on it will instead be called:

• • SnomedCT_ManagedServiceUS_PRODUCTION_US1000124_20230301T120000Z.zip

Note: The change to the naming convention only effects the zip package name and the top two folders in the unzipped package. No other folder or file name contained in the release package will be impacted.

3.3.2.2. Transitive Closure Resources package naming convention

Please be aware that as of the March 2023 Release of the US Edition onwards, the Transitive Closure Resources package naming convention has been changed in order to bring it in line with the naming standards. This is being changed from:

• • SnomedCT_TransitiveClosureResourcesRF2_PRODUCTION_[date]T[time]Z.zip

...to the following:

• • SnomedCT_ManagedServiceUSTransitiveClosure_PRODUCTION_US1000124_[date]T[time]Z.zip

So, for the March 2023 Release of the US Edition, for example, the RF2 package would have originally been called:

• • SnomedCT_TransitiveClosureResourcesRF2_PRODUCTION_20230301T120000Z.zip

...whereas from now on it will instead be called:

• • SnomedCT_ManagedServiceUSTransitiveClosure_PRODUCTION_US1000124_20230301T120000Z.zip

Note: The change to the naming convention only effects the zip package name and the top two folders in the unzipped package. No other folder or file name contained in the release package will be impacted.

3.3.3. RF2 package format

Similar to the International Edition, the US Edition will follow the technical specifications for RF2 packaging format.

For future reference, the RF2 package convention dictates that it contains all relevant files, regardless of whether or not there is content to be included in each particular release. Therefore, the package contains a mixture of files which contain both header rows and content data, and also files that are intentionally left blank (including only a header record). The reason that these files are not removed from the package is to draw a clear distinction between

1 ...files that have been deprecated (and therefore removed from the package completely), due to the content no longer being relevant to RF2 in this or future releases, and 

2. ...files that just happen to contain no data in this particular release (and are therefore included in the package but left blank, with only a header record), but are still relevant to RF2, and could therefore potentially contain data in future releases.

This allows users to easily distinguish between files that have purposefully been removed or not, as otherwise if files in option 2 above were left out of the package it could be interpreted as an error, rather than an intentional lack of content in that release. 

3.3.4. Deprecation of the ICD10 Exemplar file

Due to the perceived lack of audience for this file, the US have deprecated it by removing it from the ICD10CM Map Resources package from the September 2023 US Edition Release onwards.  Please let the US NRC know if this causes any specific problems for you or your users.

• • doc_Icd10MapTechnicalGuideExemplars_Current-en-US_US1000124_20230301.xlsx

3.3.5. Changes to the Identifier file format

In line with the proposals documented here:  https://confluence.ihtsdotools.org/mag/snomed-international-proposal-to-change-the-rf2-identifier-file-specification - the US Edition Release will from now on include the following changes to the format of the Identifier files:

• < identifierSchemeId    alternateIdentifier    effectiveTime    active    moduleId    referencedComponentId           ...to
• > alternateIdentifier    effectiveTime    active    moduleId    identifierSchemeId    referencedComponentId

These improvements are introduced in the September 2023 US Edition release, and will be used in all future US Edition releases until further notice.

3.3.6. Notice of changes to the US Edition Release package

In line with the new implementation of Annotations, two new refsets have been added to the International Edition Release package, from December 2023 onwards:

• • der2_scsRefset_ComponentAnnotationStringValueSnapshot_INT_20231201.txt
  • der2_sscsRefset_MemberAnnotationStringValueSnapshot_INT_20231201.txt

The latest version of the US Edition release is based upon the January 2024 International Edition, and therefore these Annotations file types will also be included in the US Edition release package from the March 2024 US release onwards, until further notice:

• • der2_scsRefset_ComponentAnnotationStringValueFull_US1000124_20240301.txt
    
  • der2_scsRefset_ComponentAnnotationStringValueSnapshot_US1000124_20240301.txt
    
  • der2_sscsRefset_MemberAnnotationStringValueFull_US1000124_20240301.txt
    
  • der2_sscsRefset_MemberAnnotationStringValueSnapshot_US1000124_20240301.txt

These refset files are empty for the March 2024 US Edition release, whilst content is being authored for future editing cycles. 

Please see the SNOMED CT Release File Specifications notes for more information on Component Annotations String Value Reference Sets and Member Annotations String Value Reference Sets.

3.4. Feedback and suggestions

We welcome questions, comments or suggestions to improve the quality, accuracy and usability of the SNOMED CT US Edition. Please send feedback to NLM Customer Support https://support.nlm.nih.gov/.