1. Introduction

1.1. Background

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.

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.

1.2. Purpose

This document provides a summarized description of the content changes included in the March 2023 release of SNOMED Clinical Terms^® (SCT) International Release.

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

The SNOMED International Release Notes are available alongside the March 2023 International release.

1.3. 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.

1.4. Audience

The audience includes National Release Centers, WHO-FIC release centers, vendors of electronic health records, terminology developers and managers who wish to have an understanding of changes that have been incorporated into the March 2023 International release.

Please note, you may have to register for a Confluence user account in order to access the links included in these release notes.

2. Content Development Activity

2.1. Summary

Continuous quality improvement and enhancement of existing content is an ongoing process undertaken by SNOMED International in preparation for every release. The March 2023 International Release has seen a continuation of the work driven by contributions from: Kaiser Permanente i.e. Convergent Medical Terminology (CMT), Global Medical Device Nomenclature Agency (GMDNA), Orphanet and other domain specific collaborations as well as requests received via the Content Request System (CRS). 

Additionally quality improvement activities are advanced via project driven initiatives summarized below.  Additional work items impacting every release are updates to the SNOMED CT derived maps such as ICD-10 and ICD-O; details are included in these release notes.  

Information about editorial decisions may be found in the SNOMED CT Editorial Guide; mapping guidance for ICD-10 can be found here.

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 March 2023. 

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. 

2.2.1.  Inactivation of 6920004 |Defect (morphologic abnormality)

As referenced in this briefing note work is underway to inactivate 6920004 |Defect (morphologic abnormality)| and remodel content that is impacted by this inactivation.

There have been changes to the value of the 363700003 |Direct morphology (attribute)| relationship for approximately 42 subtype concepts of 53941002 |Closure of septal fenestration of heart (procedure)|.

2.2.2. Review of Concepts Defined by Stated = 105590001 |Substance (substance)|

Concepts in various hierarchies (including Procedure, Clinical finding, Observable entity, Event and Specimen), which were defined by the stated attribute value of 105590001 |Substance (substance)| have been reviewed.

A set of concepts have been remodeled by removing the attribute/value relationship providing that this change does not result in a change to the meaning of the associated concepts.

A set of concepts have been remodeled by assigning a more specific substance.

A number of the grouper concepts have been inactivated, specifically the groupers that were classification derived and /or had only one subtype. This change is part of the Substance-Drug project work and will allow for the correct subsumption of the subtypes once the attribute values (where applicable) are changed to subtypes of 373873005 |Pharmaceutical / biologic product (product)|.

2.3. Body Structure 

2.3.1. Inactivation of 278843004|Structure of esophageal segment (body structure)|

Concepts referring to segments of the esophagus have been inactivated with reason ambiguous and have been replaced by specific upper/lower thoracic esophagus, or upper/lower third of esophagus concepts.

2.3.2. Addition of Subtypes for 280231002|Structure of branch of maxillary nerve (body structure)|

A small number of missing branches of the maxillary nerve and some 'entire' versions of other nerves have been added. 

2.3.3. Addition of Subtypes for 280308004|Structure of trunk of vagus nerve (body structure)|

Work has been undertaken to provide more clarity to the structure of the vagus nerve trunk along with the addition of segment descriptions.

2.3.4. Addition of Content for Peripheral Nerves

Structure of peripheral nerve of thorax (body structure) has been added and some rationalisation of the peripheral nerves of the limbs has also been implemented.

2.3.5.  SEP and Laterality Anatomy Reference Sets

The release file for the lateralizable body structure reference set has been updated and validated.

The release file for the SEP reference set has been updated and validated.

2.4. Clinical Finding

2.4.1. Positive and Negative Measurement Findings

The positive and negative measurement findings content (~300 concepts) have been updated as follows:

1. The FSN and PT has been updated to include “detected” or “not detected.” Existing descriptions with “positive” or “negative” have been retained as synonyms.

2. The 363713009 |Has interpretation (attribute)| value of 10828004 |Positive (qualifier value)| or 260385009 |Negative (qualifier value)| has been updated to 260373001 |Detected (qualifier value)| or 260415000 |Not detected (qualifier value)|.

Note: Certain areas of content did not follow the above changes, including:

• The FSN of disorder concepts have not been updated because “positive” or “negative” is part of the recognized disease name, e.g, Rheumatoid factor and anti-citrullinated protein antibody positive rheumatoid arthritis (disorder). The 363713009 |Has interpretation (attribute)| value was updated as described above so the existing classification would be preserved.

• “False positive” and “False negative” concepts were excluded.

• Pregnancy test findings were excluded.

• Blood group findings were excluded, e.g., Blood group B Rh(D) negative (finding).

• Clinical tests were mainly excluded from these updates, e.g., 112001000119100 |Positive screening for depression on Patient Health Questionnaire 9 (finding)| and 298695003 |Bragard test negative (finding)|.

Any measurement findings that were missed or where it is subsequently determined they can be updated will be changed in a future release.

Please see the briefing note (20221116 BN Positive_Negative measurement findings.pdf) for more information.

2.4.2. Myeloid Neoplasm Content Updates

The Pathology Clinical Reference Group have identified content that is outdated and modeled inconsistently in the neoplastic morphologies and related disorders. This content does not represent prevailing pathology knowledge as expressed by pathologists and other international subject matter experts, and described in the WHO Blue Books, 5th edition.

A pilot project focussing on <<414792005 |Myeloid neoplasm (morphologic abnormality)| (91 descendants) and related disorder concepts 25333006 |Myeloproliferative disorder (disorder)| and its 117 descendants) has been completed. 

The work has included addition of new content, inactivation of outdated concepts, and updating of descriptions where necessary to align with the WHO Blue Books.

2.4.3. New Primary Malignancy Disorder Concepts

Approximately 150 new primary malignancy disorder concepts have been added to SNOMED CT.

Inferred subtypes of 372087000 |Primary malignant neoplasm (disorder)| that in the past were assigned by the classifier based on the morphology hierarchy (now revised), but which did not state primary in the FSN ('agnostic') have been reviewed. These previous subtypes of 372087000 |Primary malignant neoplasm (disorder)| now have a new subtype concept added that states 'primary' to provide an option for selection by clinicians.

2.4.4. Neoplasm of Connective and Soft Tissue Disorders

Around 30 concepts which include “neoplasm of connective and soft tissue" in their FSN have been inactivated with reason "Classification derived component." 

2.4.5. Inactivation of Metastatic Content

• 75 disorder concepts of the type 'Malignant tumor involving [x structure] by [separate] metastasis from [y structure]'
• 30 disorder concepts of the type 'Metastasis to [x structure] of unknown primary' 

have been inactivated.

Examples:

• • 369554006 Malignant tumor involving right fallopian tube by separate metastasis from left fallopian tube (disorder)
  • 285643007 |Metastasis to adrenal gland of unknown primary (disorder)|

Current Editorial Guidance indicates that the primary malignancy and the metastatic malignant neoplasm should be recorded using two separate SNOMED CT concepts. Replacement concepts have been provided as the inactivation target value and where not available these concepts have been created.

A small number of remaining concepts with 'malignancy from [x body structure[ metastatic to [y body structure]' have been inactivated and replacement concepts provided.

2.4.6. Review 16356006|Multiple pregnancy (disorder)| and Subtypes

16356006|Multiple pregnancy (disorder) has been remodeled to become a subtype of 77386006 |Pregnancy (finding)|.

The subtypes of 16356006|Multiple pregnancy (disorder) have been reviewed and remodeled with some of the subtypes retaining the semantic tag ‘disorder’ where the concept meets the criteria of being always and necessarily an abnormal clinical state.

A new parent has been assigned on a concept-by-concept basis designated by whether the semantic tag has been changed. This is to ensure that a disorder is a descendant of 64572001|Disease (disorder)| and that a finding is not.

2.4.7. Changes to Preterm/Premature/Term Infant Content

Following a member request to align with global definitions that define premature/preterm as less than 37 completed weeks (259 days) of gestation the following changes have been made:

Inactivated

• 310527001 |Baby premature 39 weeks (finding)|
• 310528006 |Baby premature 38 weeks (finding)|
• 310529003 |Baby premature 37 weeks (finding)|

Replacement concept added

• 1268668007 |Term infant 39 weeks (finding)|
• 1268666006 |Term infant 38 weeks (finding)|
• 1268667002 |Term infant 37 weeks (finding)|

2.4.8. Inactivation of 230298007 |Disorder presenting primarily with chorea (disorder)

230298007 |Disorder presenting primarily with chorea (disorder)| has been inactivated.

271700006 |Chorea (finding)| was modified to 271700006 |Chorea (disorder)| with an improved definition and improved subsumption.

2.4.9. Inactivation of 307844003 |Minor surgery status (finding)| and Subtypes

Concepts that have explicit context should be in the situation hierarchy. Therefore 307844003 |Minor surgery status (finding)| and 5 subtypes with context "done" plus a procedure have been inactivated.

One concept 314471005 |Minor surgery done (finding)| was inactivated and replaced by a new concept 1268934004 |Minor surgery done (situation)|

2.5. Procedure

2.5.1. Remodel of 386745004|Transurethral cystoscopy (procedure) Hierarchy

Improvements have been made to the hierarchy of 386745004 |Transurethral cystoscopy (procedure)| with remodel and restructuring of descendant concepts.

2.5.2. Inactivation of 234784009|Insertion or fixation of tooth restoration (procedure)

234784009 |Insertion or fixation of tooth restoration (procedure)| has been inactivated with reason ambiguous and approximately 25 subtype concepts have been remodeled.

2.5.3. Inactivation of 712471003|Restorative dental procedure on tooth (procedure)|

In consultation with the Dentistry Clinical Reference Group, 712471003 |Restorative dental procedure on tooth (procedure) | has been inactivated with reason ambiguous.

Approximately 6 subtype concepts have been remodeled and 6 subtype concepts have been inactivated.

2.6. Collaboration/Harmonization Agreements

2.6.1. Convergent Medical Terminology (CMT)

69 new CMT concepts have been added with the focus being the injury domain.

2.6.2. Orphanet

Working in collaboration with Orphanet (http://www.orpha.net/consor/cgi-bin/index.php), content development is ongoing for rare disease concepts in SNOMED CT. Content in scope for this project is published in the annual update of the SNOMED CT to Orphanet Maps.

All of the concepts added for the Orphanet project have been mapped to ICD-10.

2.6.3. Cancer Synoptic Reporting

Cancer synoptic reports are used by many member countries to record pathology examination of cancer specimens including the College of American Pathologists (US and Canada), Royal College of Pathology (UK), Royal College of Pathology Australasia (Australia, New Zealand), PALGA (The Netherlands), Swedish Society of Pathology, and others.

For more information about this project, please see Cancer Synoptic Reporting Clinical Project Group 

2.6.4. International League Against Epilepsy (ILAE)

In line with approved harmonized terminology, this project is working on alignment including restructuring to update the hierarchy  << 313307000 |Epileptic seizure (finding)|.

Further information about the changes is available here. 

2.6.5. Gravity Project

24 new Gravity project concepts have been added. The focus areas for this content was being able to afford <x> findings as well as education and resource coordination procedures.

2.7. Internal Quality Improvement

2.7.1. Machine Readable Concept Model (MRCM) Changes

There have been no changes for the March 2023 release.

Changes that are in progress can be viewed via the MRCM Daily Build Browser

Please see early visibility for future changes to MRCM.

2.8. SNOMED CT derived products

2.8.1. ICD-10 map

The SNOMED CT to the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (© World Health Organization 1994) 2016 Version map (SNOMED CT to ICD-10 Map) is included in the SNOMED CT International release as a Baseline. The SNOMED CT to ICD-10 Map was created to support the epidemiological, statistical and administrative reporting needs of SNOMED International member countries and WHO Collaborating Centers.

The SNOMED CT to ICD-10 Map is released in Release Format 2 (RF2) only. It is located in the file der2_iisssccRefset_ExtendedMapFull_INT_20200731.txt, which is in the Map folder under Refset, in each of the three RF2 Release Type folders. 

The SNOMED CT to ICD-10 Map is released as Refset 447562003 |ICD-10 complex map reference set (foundation metadata concept)|.

The ICD-10 Mapping Technical Guide (including exemplars) is hosted here https://confluence.ihtsdotools.org/display/DOCICD10

2.10.2. Content Development Activity Summary

The map is a directed set of relationships from SNOMED CT source concepts to ICD-10 target classification codes.  The SNOMED CT source domains for the MAP are limited to subtypes of 404684003 |clinical finding|, 272379006 |event| and 243796009 |situation with explicit context|.  The target classification codes are ICD-10 2016 release. 

Mapped content for March 2023

The map provided for the March 2023 release has been updated, and now represents a complete map from SNOMED CT International release to ICD-10 2016 version.

• 315 newly authored concepts have been added and mapped.

• The SNOMED to ICD-O (morphology) map has 11 additional concepts added as a result of the ICD-O 3.2 review or added due to CRS requests. 

We would welcome feedback on any issues that users of the map may detect when using the map. Issues should be submitted via mapping@snomed.org

2.8.2. SNOMED CT to OWL conversion and classification

The repository containing the toolkit enabling simple SNOMED CT to OWL conversion and classification can be found here, including documentation on its use: https://github.com/IHTSDO/snomed-owl-toolkit

Please contact SNOMED International at support@snomed.org if you would like to provide any feedback on ways to extend and improve the new toolkit.

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 time within the new monthly editing cycles, 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.  

For the current SNOMED CT International edition, the following Known Issues were identified, and agreed to be resolved in future editing cycles:

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 in the latest release.  They can also be issues found during testing of the current release, which were resolved before the final deployment of the Production release.  Finally they can be issues which were reported or found during the testing phase, but which have been closed without any action taken.  

The Resolved Issues for the current SNOMED CT International edition can be found here:

3.3. Technical updates

3.3.1. RF2 package 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 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 

• 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.

Configuration file in the RF2 package, containing Release Metadata 

A new file has been included since the July 2020 International Edition, containing metadata about the Release package itself.  This has been created in conjunction with feedback from the community, and as such initially contains the following fields:

• effectiveTime
  

• previouslyPublishedPackage

• languageRefset(s)

• licenceStatement

The file is in .JSON format, to ensure that it is both machine-readable and human-readable, and is named "release_package_information.json".

The metadata will be extended and refined going forward, in order to ensure that it contains the most useful information possible. If you have any ideas about any other useful information to include, please send them to info@snomed.org, along with a business case explaining how the information would benefit stakeholders.  Please be aware that this use case will then be assessed by SNOMED International, and the new metadata will only be included in the configuration file if the business case is strong enough.  

3.3.2. Early visibility of impending changes in the upcoming 2023 Monthly International Edition releases

Please see the early visibility page for details of forthcoming changes: https://confluence.ihtsdotools.org/display/RMT/2023+Early+Visibility+Release+Notifications