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 SNOMED CT International Edition and the US Extension of SNOMED CT. The US Edition eliminates the need for implementers to manually combine the US Extension and International releases. The SNOMED CT to ICD-10-CM map reference set is to support semi-automated generation of ICD-10-CM codes from clinical data encoded in SNOMED CT for reimbursement and statistical purposes.

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. 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 for the NLM maintained SNOMED CT to ICD-10-CM mapping reference set found in the March 2018 release of the SNOMED Clinical Terms^® US Edition. These release notes also include 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 2018 US Edition release (https://www.nlm.nih.gov/healthit/snomedct/us_edition.html). 

The mapping methodology follows closely that of the SNOMED CT to ICD-10 Crossmap Project, a collaborative project between SNOMED International and the World Health Organization. Dual independent mapping by trained terminology specialists is employed to assure quality and reduce variability. Identical maps created independently are accepted as final, while discordant maps are reviewed by a third expert. Regular team meetings are held to discuss problematic and ambiguous cases.

1.2 Scope

This document covers the characteristics of this release of the map, including concept counts and file format. For details about how the map is created please refer to the technical specifications for SNOMED CT to ICD-10-CM map (https://confluence.ihtsdotools.org/display/RMT/SNOMED+CT+Managed+Service+-+US+Edition+Mapping+SNOMED+CT+to+ICD-10-CM+Technical+Specifications+-+March+2018). The Map corresponds to the March 2018 release of the US Edition of SNOMED CT (https://www.nlm.nih.gov/healthit/snomedct/us_edition.html) and the 2018 version of ICD-10-CM.

1.3 Purpose of the Map

• To provide a semi-automated coding of ICD-10-CM statistical classification data from a clinical record which is clinically encoded in SNOMED CT
• For development of ICD-10 classification codes from SNOMED CT encoded records for use in registries and diagnosis groupers
• Please note - this Map is NOT a completely automated ICD-10-CM coding from a SNOMED CT source. 

1.4 Audience

All parties who wish to understand the Map and/or to employ it for semi-automatic translation between SNOMED CT and ICD-10-CM should read this document. This may include vendors of electronic health records, terminology developers and managers. 

2 Cross map content overview

2.1 Summary

The March 2018 SNOMED CT US Edition (20180301) publication of the the SNOMED CT to ICD-10-CM map marks the first release with the mapping tooling and map release production provided by SNOMED International Managed Service. Quality assurance of the release was completed by both NLM and SNOMED International. 

2.2  Scope of publication

The MAP is a directed set of relationships from SNOMED CT source concepts to ICD-10-CM  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|.

2.2.1 March 2018 SNOMED CT to ICD-10-CM refset statistics

This map release includes a total of 199,611 map records, with a maximum of 26 map records per map group. 

2.3  What is a refset?

A Reference Set (refset) is a set of references to SNOMED CT components which may associate additional properties with members of the set. It may also indicate associations between members of the set or between members of the set and content of another nomenclature, classification or knowledge structure. The uses of Reference sets include identification of subsets of SNOMED CT content, representation of alternative hierarchical structures and cross maps to classifications. References Sets are a part of SNOMED CT Release Format 2 that provides a general purpose extensibility mechanism. Refsets are a SNOMED International standard artifact that complies with the technical specifications documented in the documentSNOMED CT Release Format 2.0 Reference Set Specifications, accessible on line as part of the Technical Implementation Guide

This publication of the MAP employs a Descriptor refset, an Extended Map refset and a Module Dependency refset as documented in that publication. 

2.4 RF2 refsets in this publication 

The SNOMED CT to ICD-10-CM map is released in RF2 format within the SNOMED CT 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_20180301.tsv) contained within the documentation folder in both the US Edition release and standalone download.

The SNOMED CT to ICD-10-CM map is released as Refsetid 6011000124106 | ICD-10-CM extended map reference set (foundation metadata concept)|.

The SNOMED CT to ICD-10-CM map refset data are contained in three separate files: 

• Extended Map: contains the core of the Map data. There are one or more map records for each source concept mapped, including the ICD-10-CM target codes. Found in the Map folder under Refset in the Full, Snapshot, and Delta Release Type folders: xder2_iisssccRefset_ExtendedMap[Full-Snapshot-Delta]_US1000124_20180301.txt. 
• Refset Descriptor: contains metadata from the SNOMED CT metadata hierarchy (children of 9000000000000454005 |foundation metadata concept|) which describes the attributes of the publication refsets and their information content
• Module Dependency: designates the versions of other SNOMED CT modules upon which this publication of the MAP depends

In this 20180301 release, the data found in the Full, Snapshot, and Delta releases are all the same. Please see 4.3.1 Improved SNOMED CT to ICD-10-CM Reference set data, for more information regarding this technical improvement. 

2.5 Spreadsheet dataset for browsing

To support browsing and understandability of the MAP, a tab delimited UTF-8 dataset which can be imported into spreadsheet software such as Microsoft Excel® is included with the release.  This can be loaded with the text import features of Excel and most spreadsheets.  The spreadsheet data format mimics the exemplar appendices of the technical documentation and is a “readable” version of the Map that can be understood by a non-technical individual. This file is not in RF2 format and can be found in the Documentation directory. 

2.6 Technical documentation

Technical documentation which summarizes the rationale, procedures, technical artifacts and project overview is included with the publication as the pdf file:  SNOMED CT Managed Service - US Edition Mapping SNOMED CT to ICD-10-CM Technical Specifications - March 2018. Accompanying the technical documentation is a collection of sample maps available as Appendix_icd_10_cm_exemplar_20180301.xlsx.

3 Technical Notes

3.1 Summary

This section of the document provides a summary of known technical issues and current changes. Please see the (tech spec doc link here) for additional information. 

3.2 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 map editing cycle, to the risk of impact to the stability of the Map if the fix were to be deployed at that stage in the Product lifecycle. For the SNOMED CT to ICD-10-CM map, the following Known Issues were identified, and agreed to be resolved in the next editing cycle:

There are no Known Issues identified in this release of the SNOMED CT to ICD-10-CM reference set.

3.3 Technical Updates

3.3.1 Improved SNOMED CT to ICD-10-CM Reference set data

As reported in section 2.3, starting with the March 2018 US Edition release the 6011000124106 | ICD-10-CM complex map reference set (foundation metadata concept)| data will adhere to SNOMED CT RF2 specifications. The 20180301 US Edition release will act as a baseline and the 6011000124106 | ICD-10-CM complex map reference set (foundation metadata concept)| data are the same in the Full, Snapshot, and Delta releases. 

Going forward (starting with the 2018 September SNOMED CT US Edition, 20180901), new 6011000124106 | ICD-10-CM complex map reference set (foundation metadata concept) data will be found in the Delta, current status data in the Snapshot, and a historical record of the refset data in the Full Release.  

Previous (historical) map data may be obtained by appending previous standalone map release files.

3.3.2. Improved Standalone Reference set naming convention

To maintain SNOMED CT RF2 file naming convention for refset products, the NLM SNOMED CT to ICD-10-CM standalone release package was updated. The new package will follow the naming convention used for all products and derivatives: 

SnomedCT_[Product][Format(optional)]_[Release Status]_[Release date]T[Release time][time zone]

No longer in use: 

der2_Refset_ICD10CM_US_20170901.zip 

The newly named NLM SNOMED CT to ICD-10-CM standalone refset package: 

SNOMEDCT_USICD10CMUStoICD10CM_PRODUCTION_20180301T120000Z

4 Quality assurance and maintenance

Mapping procedures as outlined in the technical documentation consist of dual independent mapping of all source concepts with map records sent to publication only after consensus of the independent mappers is reached. The Map will be periodically updated with new versions of SNOMED CT and ICD-10-CM. Future expansion of coverage of SNOMED CT concepts will depend on user feedback and availability of resources.

5 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/ics/support/default.asp?style=classic&deptID=28054&category=snomed_ct 

6 Appendix: File format specifications

6.1 Refset Descriptor refset (xder2_cciRefSet_DescriptorSnapshot_INT_yyyymmdd)

(der2 designates a data file of format RF2; cci denotes a Concept-Concept-Integer refset; INT identifies the international version; yyyymmdd is the year, month and date of publication)

6.2 Module Dependency refset (xder2_ssRefSet_ModuleDependencySnapshot_INT_yyyymmdd)

6.3 Extended Map refset (xder2_iissscRefset_ExtendedMapSnapshot INT_yyyymmdd)

6.4 Map browser spreadsheet (tls_ICD10HumanReadableMap_INT_yyyymmdd)

The browser spreadsheet dataset is the same as the Extended Map Refset with the descriptive names for the SNOMED CT concept, ICD-10-CM code and mapCategoryId added for readability.