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Unified Medical Language System® (UMLS®)

The CORE Problem List Subset of SNOMED CT®

The Clinical Observations Recordings and Encoding (CORE) Problem List Subset is a UMLS CORE Project with the purpose of defining a UMLS subset that is most useful for documenting and encoding clinical information at a summary level. The CORE Problem List Subset includes SNOMED CT concepts and codes that can be used for the problem list, discharge diagnoses, or reason of encounter.

For older CORE Problem List Subset Release Files, please see the SNOMED CT Archives page.

Current CORE Problem List Subset

Version: November 2023

Derived from SNOMED CT version: September 2023 US Edition of SNOMED CT

Derived from UMLS Metathesaurus version: 2023AB

Download Release

Additional Information


A key aspect of the UMLS CORE 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 original subset was 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). From the 201208 version onwards, problem list data from the Veterans Administration have also been incorporated. The most frequently used 16,874 terms that cover 95% of usage volume in each institution are mapped to UMLS concepts using lexical matching supplemented by manual review.

Through the UMLS, mappings from the local terms to SNOMED CT concepts are identified. This constitutes the CORE Problem List Subset of SNOMED CT. Unmapped local terms that are considered useful for the problem list are submitted to the International Health Terminology Standards Development Organisation (IHTSDO). If accepted, the new SNOMED CT concepts are added to the CORE Subset. As SNOMED CT is the designated U.S. standard terminology for diagnosis and problem lists, and one of the requirements of the ‘Meaningful Use’ criteria of the Electronic Health Record, we believe that identifying a frequently used 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 Terminology Services (UTS) include a SNOMED CT browser that may be used for this purpose. The SNOMED CT Browser is available through the Applications menu of the UTS. 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:

  • Only active SNOMED CT concepts are included
  • All concepts are chosen from the following 4 hierarchies: Clinical finding, Procedure, Situation with explicit context, and Events
  • Within the Clinical finding hierarchy, when two very similar concepts exist e.g. ‘12441001 Epistaxis (disorder)’ and ‘249366005 Bleeding from nose (finding)’, the disorder concept is favored
  • Procedures are included in the CORE subset because they occur in some problem lists. However, some institutions keep a separate procedures list (not included in the generation of the CORE Subset). Some terms (< 100) are intended to indicate the past occurrence of a procedure e.g. ‘Personal history of cardiac catheterization’. These are mapped to the corresponding SNOMED CT concepts when such exist (typically in the Situation with explicit context hierarchy). When no such SNOMED CT concepts exist, they are mapped to the procedure itself. If users think it is necessary, the precise meaning can still be expressed by post-coordinating the procedure as the associated procedure attribute to the concept ‘416940007 Past history of procedure (situation)’, or by using special flags in their information model
  • Terms that indicate the presence of a medical device e.g. ‘Heart Valve Prosthesis’ are mapped to the procedure of introducing the device ‘307279007 Prosthetic replacement of heart valve (procedure)’ when no more appropriate SNOMED CT concepts exist

Mapping to ICD-9-CM and ICD-10-CM

In the migration to SNOMED CT as the primary clinical terminology for patient problems (diseases and conditions), it is desirable that the legacy ICD-9-CM data be translated to SNOMED CT. We have published a ICD-9-CM to SNOMED CT map to facilitate this translation.

We have also created a SNOMED CT to ICD-10-CM map to support semi-automated generation of ICD-10-CM codes from clinical data encoded in SNOMED CT for reimbursement and statistical purposes.

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 such as additional synonyms (beyond those present in SNOMED CT itself), text definitions for many terms, and corresponding codes in other terminologies.

File Description

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

  • SNOMED_CID – conceptId of the SNOMED CT concept
  • SNOMED_FSN – SNOMED CT fully-specified name
  • SNOMED_CONCEPT_STATUS – concept status of the SNOMED CT concept
  • UMLS_CUI – the corresponding UMLS concept identifier, if concept is not yet in the UMLS this will be NA (not available)
  • OCCURRENCE – number of institutions having this concept on their problem list (from 1 to 8), not populated for concepts retired from Subset
  • USAGE – the average usage percentage among all institutions (i.e. sum of individual usage percentages divided by 8), not populated for concepts retired from Subset
  • FIRST_IN_SUBSET – the version of Subset first containing this concept
  • IS_RETIRED_FROM_SUBSET – in future, some concepts will be marked retired if they are retired by IHTSDO or no longer considered to be useful e.g. when there are more appropriate SNOMED CT concepts
  • LAST_IN_SUBSET – the version of Subset last containing this concept, only populated for concepts retired from Subset
  • REPLACED_BY_SNOMED_CID - SNOMED CT concept to replace concept retired from Subset, only populated for concepts retired from Subset

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 after each UMLS release to synchronize with the latest version of the SNOMED CT U.S. Edition. 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). The NLM is the U.S. Member of the IHTSDO and, as such, distributes SNOMED CT at no cost in accordance with the Member rights and responsibilities outlined in the IHTSDO's Articles. The license terms are incorporated into the License for Use of the UMLS Metathesaurus. Use of SNOMED CT is subject to the IHTSDO Affiliate license provisions and is free in IHTSDO Member territories including the United States, in low income countries, and for Qualifying Research Projects in any country.

To request a license click "Sign Up" on the UTS Homepage. Additional information can be found on the UMLS License page.

Feedback and Suggestions

We welcome any questions, comments or suggestions that would improve the quality, accuracy, and usability of the subset. Please send feedback through the NLM Customer Support form.


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: August 29, 2018