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 July 2021 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 September 2021 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 September 2021 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 July 2021 International Edition - SNOMED International Release notes. 

2 Content Development Activity 

2.1 Summary

The September 2021 SNOMED CT US Edition marks the eighth 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 September 2021 US Edition of SNOMED CT Statistics 

These statistics include the active content from the July 2021 International Edition and the September 2021 US Edition.

These statistics include the content from the September 2021 US Extension.

2.2 SNOMED CT derived products 

2.2.1 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. 

2.2.2 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). 

The Route of Administration concepts are now maintained as a value set on 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

2.2.3 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 July 2021 International Edition - SNOMED International Release notes), the following are Known Issues for the SNOMED CT 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 September 2021 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 July 2021 International Edition - SNOMED International Release notes), the following Resolved Issues for the SNOMED CT September 2021 US Edition:

3.3 Technical Updates

In addition to the Technical Updates reported in the SNOMED CT July 2021 International Edition - SNOMED International Release notes, the following technical updates pertain to the US Edition: 

3.3.1 Concrete Domains launch

Following on from the successful technical preview of the impending Concrete Domains changes, released in February 2021, SNOMED International are now implementing the changes in the July 2021 International Edition Production release. This contains drug concept strengths and counts expressed as concrete values in a new Relationships file. The RF2 Release package for July 2021 therefore incorporates the following changes:

• Inferred Relationship file changes:
  
  • All relationships for values of strength and count for medical products inactivated

  • All relationships for attributes of strength and count for medicinal products inactivated

  • New relationships for new concept model data attributes of strength, count, product name, and supplier for medicinal products will be added 

• Stated OWL Axiom file changes:

• Existing drug concept axioms updated to use concrete values
• Existing strength and count attribute types will be inactivated, replaced with new ones using the same FSNs.
• New Inferred "Relationship Concrete Values" files:
  • New concrete values relationship files added to the RF2 package structure, containing all new relationships for values of strength and count for medical products:
    • sct2_RelationshipConcreteValues_Delta_US1000124_20210901.txt
    • sct2_RelationshipConcreteValues_Full_US1000124_20210901.txt
    • sct2_RelationshipConcreteValues_Snapshot_US1000124_20210901.txt
• MRCM file changes:
• MRCM includes new rows to indicate that the new attribute types are expected to take a concrete domain - specifically numbers - as target values.

3.3.2 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. 

3.4 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/.