The CORE Problem List Subset of SNOMED CT®

Data Files
(expect a new version of the subset for each new release of SNOMED CT and the UMLS Metathesaurus)

CORE Problem List Subset VersionDerived from SNOMED CT versionDerived from UMLS Metathesaurus version
SNOMEDCT_CORE_SUBSET_200911 July 2009 International Release 2009AB
SNOMEDCT_CORE_SUBSET_200908 July 2009 International Release 2009AA
SNOMEDCT_CORE_SUBSET_200907 January 2009 International Release 2009AA

Introduction

The CORE Problem List Subset of SNOMED CT® is an output of the UMLS CORE Project (CORE stands for Clinical Observations Recording and Encoding). The purpose of the UMLS CORE Project is to define a UMLS subset that is most useful for documentation and encoding of clinical information at a summary level, such as problem list, discharge diagnosis or reason of encounter. A key aspect of the Project is the collation and analysis of datasets collected from health care institutions that utilize controlled vocabularies for data entry. These datasets contain the list of controlled terms and their actual frequency of usage in clinical databases.

The present subset is based on datasets submitted by 7 institutions - Beth Israel Deaconess Medical Center, Intermountain Healthcare, Kaiser Permanente, Mayo Clinic, Nebraska University Medical Center, Regenstrief Institute and Hong Kong Hospital Authority. These institutions are large-scale, mixed inpatient-outpatient facilities that cover most major medical specialties (including Internal Medicine, General Surgery, Pediatrics, Obstetrics, Gynecology, Psychiatry and Orthopedics). The most frequently used 14,000 terms that cover 95% of usage volume in each institution are mapped to 6,800 UMLS concepts. This forms the basis of the UMLS CORE subset. About 8% of terms are not mappable to the April 2009 edition of the UMLS Metathesaurus.

Among the source terminologies in the UMLS, SNOMED CT covers the highest percentage (81%) of the UMLS CORE concepts. As SNOMED CT is the designated U.S. standard terminology for diagnosis and problem lists, we believe that identifying a CORE subset of SNOMED CT concepts will be useful to users who want to implement SNOMED CT in their clinical systems.

Purpose and use of subset

The main purpose of the SNOMED CT CORE subset is to facilitate the use of SNOMED CT as the primary coding terminology for problem lists or other summary level clinical documentation. The use of a common list of SNOMED CT concepts will maximize data interoperability among institutions. Local problem list vocabularies often need to expand to satisfy specific user needs. Users should check to see if SNOMED CT contains terminology for concepts they need to meet local requirements. The UMLS Knowledge Source Server includes a browser that may be used for this purpose (http://umlsks.nlm.nih.gov). When adding new concepts that are not covered by SNOMED CT, users are encouraged to follow the rules of post-coordination in SNOMED CT where possible. For instance, if a new concept ‘Left kidney stone’ is needed, it can be created by adding the qualifier concept ‘7771000 Left’ as a laterality attribute to the CORE concept ‘95570007 Kidney stone’. In this way, link to the CORE concepts is maintained and divergence of problem list vocabularies can be minimized. Institutions that are using their own problem list vocabularies are encouraged to map them to SNOMED CT with a focus on the CORE concepts to facilitate data interoperability.

Choice of SNOMED CT concepts

To find the most appropriate SNOMED CT concepts for each problem list term, the following guidelines are used:

Other appropriate CORE terms that could not be mapped to SNOMED CT will be submitted to the IHTSDO for high priority addition to SNOMED CT.

Mapping to ICD-9-CM

We recognize that problem list entries are sometimes used to generate ICD-9-CM codes for reimbursement and other purposes. In a separate NLM project, a rule-based reimbursement map from SNOMED CT to ICD-9-CM is being created. A draft map for about 5,000 SNOMED CT concepts will be available soon. There is a significant degree of overlap (about 60%) between the SNOMED CT concepts in the SNOMED CT CORE subset and the draft map. The concepts in the SNOMED CT CORE subset not yet covered by the draft map will be given priority if the scope of the reimbursement map is to be expanded in future. For some concepts, crosswalk from SNOMED CT to ICD9CM is possible through the UMLS, using the UMLS CUI included with the subset.

There may be possible demands for maps from ICD-9-CM codes to SNOMED CT concepts to cater for the situation in which clinical data is primarily coded in ICD-9-CM. However, due to the large difference in granularity between the two terminologies, such a map will be difficult to create and problematic to use (there will be a lot of one-to-many maps). We believe that SNOMED CT is much more suitable for clinical documentation and would encourage users to switch to SNOMED CT as the primary coding terminology.

Additional resources from the UMLS

For each SNOMED CT concept in the subset, the corresponding UMLS CUI is listed. Through this, users can have access to resources available in the UMLS e.g., additional synonyms (beyond those present in SNOMED CT itself), text definitions for many terms, corresponding codes in other terminologies.

File description

The SNOMED CT CORE subset data file has the following fields:

A sample database load script can be found here.

The file identifies what we hope is a useful subset of SNOMED CT, but does not include all the information likely to be required to make effective use of SNOMED CT in an application, such as synonyms that may include more clinician-friendly terms than the SNOMED CT fully-specified name. The identifiers in the file can be used to extract more complete information for these concepts from either the UMLS release files or the SNOMED CT native format files.

Update and maintenance

A new version of the subset will be published for each new release of SNOMED CT and the UMLS. Newly retired SNOMED CT concepts will be flagged and additional concepts may be added if appropriate.

SNOMED CT license requirement

SNOMED CT is owned by the International Health Terminology Standards Development Organisation (IHTSDO), of which NLM is the US Member. Use of SNOMED CT is subject to the IHTSDO Affiliate license provisions ( incorporated in the License Agreement for Use of the UMLS® Metathesaurus® as Appendix 2) and is free in IHTSDO Member countries (http://www.ihtsdo.org/members) including the United States, in low income countries (http://www.ihtsdo.org/news/article/view/ihtsdo-announces-free-use-of-snomed-ct-in-low-income-countries/), and for approved research projects in any country.

Feedback and suggestions

We welcome any questions, comments or suggestions that would improve the quality, accuracy and usability of the subset. Please send feedback to Dr. Kin Wah Fung, Lister Hill National Center for Biomedical Communications, National Library of Medicine (email: kwfung@nlm.nih.gov).

Acknowledgements

We thank the institutions that supplied datasets used to define the subset and SNOMED Terminology Solutions of the College of American Pathologists for reviewing part of the subset and giving us valuable suggestions.

Lister Hill National Center for Biomedical Communications
U.S. National Library of Medicine

Last reviewed: 06 November 2009
Last updated: 10 August 2009
First published: 20 July 2009
Metadata| Permanence level: Permanent: Dynamic Content