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Supporting Interoperability – Terminology, Subsets and Other Resources from NLM

NLM is the central coordinating body for clinical terminology standards within the Department of Health and Human Services (HHS).

  • NLM supports the development, enhancement, and distribution of clinically specific vocabularies to facilitate the exchange of clinical data and improve retrieval of health information.
  • NLM supports, licenses, or develops key Clinical Vocabularies identified for Meaningful Use and HIPAA transactions: SNOMED CT®, LOINC®, and RxNorm.
  • NLM represents the US on matters related to the structure and content of SNOMED CT, as member of the International Health Terminology Standards Development Organisation (IHTSDO®)
  • NLM provides uniform distribution for more than 150 clinical vocabulary standards and HIPAA administrative code sets through the UMLS Metathesaurus.
  • NLM coordinates efforts to develop mappings between HIPAA code sets and standard clinical vocabularies.
  • NLM supports training and research/demonstrations in informatics.
  • NLM provides high-quality consumer health information through MedlinePlus, as well as access to FDA-approved drug information through DailyMed.

We welcome your comments and questions: Contact NLM .







SNOMED CT (Systematized Nomenclature of Medicine--Clinical Terms) is a comprehensive clinical terminology that is owned, maintained, and distributed by the International Health Terminology Standards Development Organisation (IHTSDO), a not-for-profit association based in London, UK.

The NLM is the U.S. Member of the IHTSDO and, as such, distributes SNOMED CT at no cost, through Uniform Medical Language System (UMLS) Terminology Service (UTS) and the UMLS Metathesaurus. Licensees of the UMLS Metathesaurus have access to SNOMED CT in multiple formats and linked to many other biomedical terminologies and natural language processing tools. UMLS licensees also have free access to SNOMED CT in native file formats downloaded directly from the UTS.

In 2011, the IHTSDO established a “Public Good” use policy: free use of English-language SNOMED CT terms and identifiers in international research databases, in complementary health IT standards, and in other projects and resources available worldwide. The policy allows SNOMED CT to serve as a standard vocabulary for key data elements and value sets in international resources that accept input from - and are used in – both IHTSDO Member and non-Member countries.


U.S. Extension to SNOMED CT®

Listing of the concepts, descriptions, relationships and their history for terminology content accepted by the NLM as a formal extension to the SNOMED CT International Release.

The U.S. Extension:


1. Provides “rapid” access to concept IDs for use by implementers, pending action by IHTSDO on content submissions likely to be added to the SNOMED CT International Release.

2. Provides standard terminology needed for U.S. clinical use cases, but not generally useful in other countries, e.g., regulatory or legislatively mandated terms specific to the U.S.


U.S. SNOMED CT Content Request System

Allows users to request basic changes to SNOMED CT, for either the International Release of SNOMED CT or the US Extension to SNOMED CT.


Free browser searches for and displays SNOMED CT content, as included in UMLS® Metathesaurus®. Also expands searches to include synonymous terms from over 100 Metathesaurus vocabulary sources. UMLS Metathesaurus License and UTC Account required to access browser.

SNOMED International SNOMED CT Browser

Free service searches for and displays textual descriptions associated with SNOMED CT concepts. No cost or license required to use the Service.

MAPS (involving SNOMED CT and ICD-9 or ICD-10 and their Clinical Modifications)

SNOMED CT to ICD-10-CM Rule-Based Mapping and Tool (NLM)

Preview Release of subset of the Map (February 2012): 7277 SNOMED CT codes and viewer, I-MAGIC (Interactive Map-Assisted Generattion of ICD Codes).Algorithm utilizes the SNOMED CT to ICD-10-CM Map in a real-time, interactive manner to generate ICD-10-CM codes.

Second release/June 2012 (expected): 15,000 codes. Draws heavily upon the SNOMED CT to ICD-10 map.

SNOMED CT® to ICD-10 Rule-Based Mapping (prepared by SNOMED International)

Project has mapped 17,000 SNOMED CT codes to ICD-10 and is in the process of international validation of the mapping.

SNOMED CT® to ICD-9-CM Mapping (prepared by SNOMED International)

Complete map is issued every 6 months with International Release; most recent SNOMED CT release (January 2012) is current with most recent version of ICD-9-CM (October 2011).

SNOMED CT® to ICD-9-CM Rule-Based Mapping to Support Reimbursement (draft)

Draft map, consisting of approximately 5,000 concepts representing SNOMED CT terms most commonly used by Kaiser Permanente and the University of Nebraska. It relates the July 2008 International Release of SNOMED CT to the 2008 version of ICD-9-CM. It was designed to support administrative reporting and reimbursement processes originating with data sets where SNOMED CT is the core terminology for clinical descriptive purposes. It provides a validated concept-based mapping to ICD-9-CM, recognizing that in some selected cases, further processing of ICD-9-CM codes may be required for specialized business applications.

ICD-9-CM Diagnostic Codes to SNOMED CT Map

ICD-9-CM codes used in short-stay and outpatient hospitals, as reported by the Centers for Medicare and Medicaid Services (CMS) for the year 2009. Map published May 2012.

ICD-9-CM Procedure Codes to SNOMED CT Map

ICD-9-CM codes used in-patient claims data, as reported by the Centers for Medicare and Medicaid Services (CMS) for the year 2011. Map published January 2013.



Logical Observation Identifier Names and Codes (LOINC®) database provides a universal code system for reporting laboratory and other clinical observations. The database comes with a mapping program called Regenstrief LOINC Mapping Assistant (RELMA) to assist the mapping of local test codes to LOINC codes and to facilitate browsing of the LOINC results. Both LOINC and RELMA are available at no cost from NLM helps support the ongoing development of LOINC.

Available in multiple languages. Recent expansions include coverage of patient assessment instruments, genetic tests, newborn screening, and public health surveillance tests. In addition to lab tests, LOINC also includes clinical measures, imaging tests, document architecture.


Medications - RxNorm

Provides normalized names for clinical drugs and links its names to many of the drug vocabularies commonly used in pharmacy management and drug interaction software. For both prescription and many over-the-counter drugs, RxNorm now includes the National Drug File-Reference Terminology (NDF-RT) from the Veterans Health Administration, expanded set of National Drug Codes (NDCs), generic names, brand names, active ingredients, UMLS IDs; RxTerms synonyms; and dose-form classes. NEW (as of January 2012 release): inert ingredients for allergy lists.

Two RxNorm application programming interfaces (APIs), SOAP/WSDL and RESTful, are available to provide developers with functions for retrieving RxTerms data from the most current RxTerms data set.


Interface terminology derived from RxNorm for writing prescriptions and recording medication histories. Two RxTerms APIs, SOAP/WSDL and RESTful, are available to provide developers with functions for retrieving RxTerms data from the most current RxTerms data set.


Browser for several drug information sources, including RxNorm, RxTerms and NDF-RT. RxNav also provides the APIs to these three sources.


UMLS Terminology Services (UTS)

Provides interactive and programmatic access to the Unified Medical Language System® (UMLS®) and the Metathesaurus®, and related knowledge sources, i.e. specific terminologies, such as SNOMED CT. Tools and resources support distribution and integration of key terminology standards in biomedical and clinical information systems.




SNOMED CT® Subsets

CORE Problem List Subset of SNOMED CT

Subset is output of the UMLS® CORE (Clinical Observations Recording and Encoding) Project. Designed to facilitate the use of SNOMED CT as the primary coding terminology for problem lists or other summary level clinical documentation. Usage will maximize data interoperability among institutions. Optional subset for fulfillment of Meaningful Use Stage 1 Requirements related to Problem Lists.

Kaiser Convergent Medical Terminology (CMT) Subsets

Convergent Medical Terminology (CMT) is a clinician- and patient-friendly terminology, linked to U.S. and international interoperability standards and related vocabulary development tools and utilities. CMT was developed by Kaiser Permanente over many years for use within its health IT systems. CMT includes mappings to classifications and standard vocabularies such as SNOMED CT. Currently, seven primarily specialty-specific CMT problem subsets are available through the UMLS, representing almost 14,000 concepts.

Nursing Problem List Subset of SNOMED CT®

Facilitates use of SNOMED CT as the primary coding terminology for nursing problems used in care planning, patient problem lists or other summary level clinical documentation; subset is based on nursing diagnosis concepts found within the Metathesaurus.


LOINC® Subsets

LOINC Common Laboratory Orders Value Set

Defines a set of universal LOINC® codes for most frequently ordered laboratory tests, based on statistics from five clinical sources, including a state health information exchange, hospitals, referral labs. Set is recommended for use by order entry systems developers for delivery in HL7 messages to laboratories where they could be understood and fulfilled.

LOINC Top 2000+ Lab Observations and Mappers’ Guide

Subset contains 2017 most commonly reported LOINC codes, representing about 98% of the test volume carried by three large organizations that mapped all of their laboratory tests to LOINC codes.

Newborn Screening Coding and Terminology Guide

Facilitates the use of electronic health data standards in recording and transmitting newborn screening test results. Guide covers conditions recommended for screening by the Secretary's Advisory Committee on Heritable Disorders in Newborns and Children (SACHDNC) or by a state within the U.S; set continues to expand. Currently deployed in several states; more deployments anticipated in future.

Table of Example UCUM Codes for Electronic Messaging

Draft enumeration of the Unified Code for Units of Measure (UCUM), designed to identify what the UCUM syntax would produce for specific unit patterns in electronic communication. The Unified Code for Units of Measure is a code system intended to include all units of measures being contemporarily used in international science, engineering, and business. Its purpose is to facilitate unambiguous electronic communication of quantities together with their units.

Subsets for Test Panels & Assessment Forms (including CMS survey instruments)

Export of a key subset of the Panels and Forms represented in LOINC. The entire package of this key subset is currently available, in addition to separate packages for Laboratory panels, Clinical panels, Consumer Health panels, HEDIS panels, the HL7 Clinical Genetics panels, Newborn Screening panels, PhenX panels, US Government panels (including the CMS survey instruments MDSv2, MDSv3, OASIS, and CARE), and Other Survey Instruments.


RxNORM Subsets

RxNorm Current Prescribable Content

Subset of currently prescribable drugs found in RxNorm, intended to be an approximation of the prescription drugs currently marketed in the US. The subset also includes some frequently-prescribed over-the-counter drugs.



MedlinePlus Connect -- Consumer Content

Free service that links EHRs, PHRs and other health IT systems to consumer-friendly health information in English and Spanish from Accepts requests based on the following diagnosis, medication or laboratory test codes: SNOMED CT, ICD-9-CM, NDC, RXCUI and LOINC. Available as a Web application and an XML Web service.

Daily Med

Provides health information providers and the public with a standard, comprehensive, up-to-date, look-up and download resource of medication content and labeling as found in medication package inserts (“structured product labels” or SPLs), as submitted by drug companies to the Food and Drug Administration (FDA). Daily Med is supported by the DailyMed RESTful API, a web service for accessing current SPL information.


NLM-supported free APIs to facilitate development of computer and mobile applications that access its highest value datasets, including: PubMed,, Medline Plus, the Unified Medical Language System (UMLS), Genetics Home Reference, Semantic Knowledge Representation (SKR; supporting natural language processing), RxNorm and National Drug File-Reference Terminology (NDF-RT).

Language & Knowledge Processing AND Image Processing

NLM's research and development division, the Lister Hill National Center for Biomedical Communications, conducts and supports research in natural language processing to extract usable and meaningful information from biomedical text, as well as in the capture, storage, processing, retrieval, transmission, and display of biomedical documents and medical imagery.


Last Reviewed: November 5, 2018