Introduction

In 2015, the US adopted ICD-10-CM, however some legacy electronic health record (EHR) systems or healthcare data may contain clinical information encoded in ICD-9-CM. SNOMED CT is considered to be the most comprehensive, multilingual clinical healthcare terminology in the world. It is designed for use in clinical documentation in the Electronic Health Record (EHR). In the 2014 ONC Certification Criteria for EHR products (to qualify for Meaningful Use incentives) and the 2019 CMS program Promoting Interoperability, SNOMED CT was named as one of the required standards for procedures. This map is designed to support a transition from the use of legacy ICD-9-CM procedure codes to SNOMED CT.

The most useful mappings are the one-to-one maps, in which a single SNOMED CT concept can be used to represent the full meaning of an ICD-9-CM code. This allows the automatic translation of ICD-9-CM codes into SNOMED CT codes without loss of meaning. In the creation of the map, we tried to identify as many one-to-one maps as possible. However, due to the differences between the two coding systems, this is not possible for some ICD-9-CM codes. The Map is published in two separate files, one containing the one-to-one (exact) maps, and the other the one-to-many (partial) maps. In the partial maps, the target SNOMED CT concept can be broader or narrower than the meaning of the ICD-9-CM code.

Mapping Methodology

In-patient claims data for 2011 were obtained from the Centers for Medicare & Medicaid Services (CMS). Using the UMLS, we identified synonymy relations between ICD-9-CM terms (both the main rubric and inclusion entries) and SNOMED CT concepts, which formed the basis of the map. One-to-one synonymy between the ICD-9-CM rubric and a SNOMED CT concept was accepted as valid one-to-one map and not manually reviewed. One-to-many maps were manually reviewed for validity and converted to one-to-one maps if possible. Frequently-used ICD-9-CM codes which fell within the 95th percentile of usage and did not have any UMLS maps were manually reviewed for possible mappings. All target SNOMED CT codes belong to the Procedure hierarchy.

Summary Statistics (202412 Release)

Versions of Terminologies and Knowledge Sources (202412 Release)

• ICD-9-CM – the CMS data was based on the 2011 version. The 2013 version was used in the Map (ICD-9-CM had not been updated since 2011). One code from the CMS data was not current in 2013 ICD-9-CM, but was kept in the Map because obsolete codes might be present in legacy data and their maps would still be useful
• SNOMED CT – September 2024 US Edition
• UMLS – 2024AB release

Data Format (202412 Release)

The Map is published as two tab-delimited value files with the same file structure. The file ICD9CMV3_SNOMED_MAP_1TO1.txt contains the ICD-9-CM codes with one-to-one maps, and the file ICD9CMV3_SNOMED_MAP_1TOM.txt contains the ICD-9-CM codes with one-to-many maps. For completeness, the second file also contains the ICD-9-CM codes that do not have a map. The fields are:

• ICD_CODE – ICD-9-CM code
• ICD_NAME – ICD-9-CM description
• IS_CURRENT_ICD – whether ICD-9-CM code is still current in the 2013 version
• IP_USAGE - % of total code usage in in-patient claims data
• SNOMED_CID – SNOMED CT concept identifier, the target of the map (null for ICD-9-CM codes without a map)
• SNOMED_FSN – SNOMED CT fully-specified name (null for ICD-9-CM codes without a map)

License Requirements

In accordance with NLM’s mapping assumptions, the Map can be used by users who are licensed to use both SNOMED CT and ICD-9-CM. 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 free in IHTSDO Member countries including the United States, in low income countries, and for approved research projects in any country, but is subject to the SNOMED CT Affiliate license provisions (incorporated in the License Agreement for Use of the UMLS® Metathesaurus® as Appendix 2). The use of ICD-9-CM is free.

Comments and Questions

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