Clinical terminologies are currently distributed with a wide range of formats and schedules. A summary of distribution patterns for several significant terminologies is listed below.

NOTE: There is content in this document that is directly quoted from existing published literature and websites. Notably, some language has been incorporated verbatim from LOINC, RxNorm, and SNOMED CT websites, which contain overviews about the distribution of each terminology.

SNOMED CT[1]

Two versions of SNOMED CT are available to end-users, the international version and the US extension of SNOMED CT. The international version is released by SNOMED International to all member countries and affiliates. Each member country is required to nominate an organization as their National Release Center (NRC). The NRC is an official point of contact within a member country or jurisdiction that has the responsibility to serve as the interface between SNOMED International, the national users and affiliates, and other members. NRC responsibilities include receiving the International Release of SNOMED CT from SNOMED International, making it available to licensees in the Member country, and promoting and supporting adoption and deployment of SNOMED CT in the Member country. Some NRCs also provide additional products, such as SNOMED CT extensions, and services to support national use of SNOMED CT.

Beginning September 2023, the international edition packages are released on Member Licensing and Distribution Service (MLDS) on the first day of each month. Monthly releases of SNOMED CT will continue to be made available from the MLDS. The MLDS contains SNOMED International releases, both Production and Alpha (technology previews), available for Members to download.

The US Extension of SNOMED CT US Extension is maintained by the National Library of Medicine (NLM), part of the National Institutes of Health, Department of Health and Human Services, as the NRC for the US. The US Extension contains two different types of content, US-specific content and content of US origin intended for future inclusion in the international release. The US extension addresses a number of terminology needs that cannot be directly represented by the SNOMED CT international release. While the SNOMED CT international edition has moved to monthly releases, the US edition of SNOMED CT remains on the current bi-annual release schedule of March and September. The last release of the SNOMED CT US edition was March 1, 2024. Users in the US can download SNOMED CT release files at https://www.nlm.nih.gov/healthit/snomedct/us_edition.html.

A number of SNOMED browsers are available online to search the SNOMED CT terminology. The SNOMED International SNOMED CT Browser (https://browser.ihtsdotools.org/?) is available online to anyone for reference purposes. Users are able to search in SNOMED CT international release in English and Spanish, as well as search the local extension from a number of member countries.

LOINC[2]

The Regenstrief Institute maintains LOINC and makes it available in a number of file formats. Regenstrief Institute distributes LOINC and RELMA (Regenstrief LOINC Mapping Assistant) free of charge, however a LOINC username and password are required. In obtaining and using LOINC or RELMA, end users agree to the terms-of-use that are outlined at https://loinc.org/license. Users can also search the LOINC terminology using an online search tool (https://loinc.org/search/), however a LOINC username and password are required.

Updated versions of LOINC are distributed twice per year, in February and August. Between public releases, LOINC publishes a preview of new codes that were requested by users and processed for development by the LOINC team.

The full LOINC database, supporting documentation and supplemental files, and the RELMA® mapping program are available for download from the Regenstrief Institute on the LOINC website (http://loinc.org). LOINC version 2.77, released on February 27, 2024, contains the following files:

Loinc_2.77
├── AccessoryFiles
│   ├── AnswerFile
│   │   ├── AnswerFileReadMe.txt
│   │   ├── AnswerList.csv
│   │   └── LoincAnswerListLink.csv
│   ├── ChangeSnapshot
│   │   ├── ChangeSnapshotReadMe.txt
│   │   ├── LoincChangeSnapshot.csv
│   │   └── PartChangeSnapshot.csv
│   ├── ComponentHierarchyBySystem
│   │   ├── ComponentHierarchyBySystem.csv
│   │   └── ComponentHierarchyBySystemReadMe.txt
│   ├── ConsumerName
│   │   ├── ConsumerName.csv
│   │   └── ConsumerNameReadMe.txt
│   ├── DocumentOntology
│   │   ├── DocumentOntology.csv
│   │   └── DocumentOntologyReadMe.txt
│   ├── DocumentOntologyOwl
│   │   ├── DocumentOntology.owl
│   │   └── DocumentOntologyOwlReadme.txt
│   ├── GroupFile
│   │   ├── Group.csv
│   │   ├── GroupAttributes.csv
│   │   ├── GroupFileReadMe.txt
│   │   ├── GroupLoincTerms.csv
│   │   ├── ParentGroup.csv
│   │   └── ParentGroupAttributes.csv
│   ├── ImagingDocuments
│   │   ├── ImagingDocumentCodes.csv
│   │   └── ImagingDocumentCodesReadMe.txt
│   ├── LinguisticVariants
│   │   ├── LinguisticVariants.csv
│   │   ├── LinguisticVariantsReadMe.txt
│   │   ├── deAT24LinguisticVariant.csv
│   │   ├── deDE15LinguisticVariant.csv
│   │   ├── elGR17LinguisticVariant.csv
│   │   ├── esAR7LinguisticVariant.csv
│   │   ├── esES12LinguisticVariant.csv
│   │   ├── esMX28LinguisticVariant.csv
│   │   ├── etEE10LinguisticVariant.csv
│   │   ├── frBE23LinguisticVariant.csv
│   │   ├── frCA8LinguisticVariant.csv
│   │   ├── frFR18LinguisticVariant.csv
│   │   ├── itIT16LinguisticVariant.csv
│   │   ├── koKR13LinguisticVariant.csv
│   │   ├── nlNL22LinguisticVariant.csv
│   │   ├── plPL29LinguisticVariant.csv
│   │   ├── ptBR11LinguisticVariant.csv
│   │   ├── ruRU20LinguisticVariant.csv
│   │   ├── trTR19LinguisticVariant.csv
│   │   ├── ukUA30LinguisticVariant.csv
│   │   └── zhCN5LinguisticVariant.csv
│   ├── LoincIeeeMedicalDeviceCodeMappingTable
│   │   ├── LoincIeeeMedicalDeviceCodeMappingTable.csv
│   │   └── LoincIeeeMedicalDeviceCodeMappingTableReadMe.txt
│   ├── LoincRsnaRadiologyPlaybook
│   │   ├── LoincRsnaRadiologyPlaybook.csv
│   │   └── LoincRsnaRadiologyPlaybookReadMe.txt
│   ├── LoincUniversalLabOrdersValueSet
│   │   ├── LoincUniversalLabOrdersValueSet.csv
│   │   └── LoincUniversalLabOrdersValueSetReadMe.txt
│   ├── Loinc_2.77_DifferenceReport.pdf
│   ├── PanelsAndForms
│   │   ├── AnswerList.csv
│   │   ├── Loinc.csv
│   │   ├── LoincAnswerListLink.csv
│   │   ├── PanelsAndForms.csv
│   │   └── PanelsAndFormsReadMe.txt
│   ├── PartFile
│   │   ├── LoincPartLink_Primary.csv
│   │   ├── LoincPartLink_Supplementary.csv
│   │   ├── Part.csv
│   │   ├── PartFileReadMe.txt
│   │   └── PartRelatedCodeMapping.csv
│   └── Updates
│   ├── Updates.csv
│   ├── Updates.mdb
│   └── UpdatesReadMe.txt
├── LoincLicense_5.5.txt
├── LoincReadMe.txt
├── LoincTable
│   ├── Loinc.csv
│   ├── MapTo.csv
│   └── SourceOrganization.csv
├── LoincTableCore
│   ├── LoincTableCore.csv
│   ├── LoincTableCoreReadMe.txt
│   └── MapTo.csv
└── loinc.xml

LOINC names are not case sensitive. In other words, the meaning of a LOINC term is the same regardless of whether the name is represented in upper, lower, or mixed case. For the few LOINC terms that represent concepts whose names are case sensitive by international convention, such as red blood cell antigens, the Component Part and Fully Specified Name include the the word 'little' in front of each letter that is lower case, and superscripts are indicated by the word 'super'.

RxNorm[3]

The full RxNorm data set is released on the first Monday of each month by the US National Library of Medicine (NLM). During months when the first Monday is a Federal holiday, RxNorm is released the next day (i.e. Tuesday). Weekly update files are available from the NLM website for download. Users can choose to download the full RxNorm files monthly, or download only the updates since the last monthly release. https://www.nlm.nih.gov/research/umls/rxnorm/docs/rxnormfiles.html

The full monthly RxNorm release includes 9 data files, which are simple text files with pipe ('|') delimiters between each field value in Rich Release Format (RRF) with the extension ".RRF". The character set of RxNorm release files is Unicode UTF-8. However, the files are not fully normalized as would be the case in a formal database; there are duplications across and within files by design.

NLM does not provide RxNorm files in Excel format. However, RxNorm files are text files which can be imported or converted manually into a spreadsheet. For detailed instructions, see this brief video titled: Opening an RxNorm File in a Spreadsheet.

RxNorm files are in Rich Release Format with the extension .RRF, which are text files with values separated by the pipe character (|). After unzipping the RxNorm ZIP file, a text editor, such as Notepad or Notepad++ can be used to open and view the RxNorm data.

RxNorm viewer https://mor.nlm.nih.gov/RxNav/search?

RxNorm shows medications for veterinary and human use.

[1] https://confluence.ihtsdotools.org/display/DOCUSEG/SNOMED+CT+US+Extension

[2] https://loinc.org/kb/users-guide/introduction/

[3] https://www.nlm.nih.gov/research/umls/rxnorm/overview.html