> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/u/universally-unique-identifier.md).

# universally unique identifier

## universally unique identifier

A 128-bit integer used to uniquely identify information in computer systems.

#### Notes

* *Universally unique identifier* are generated by widely available algorithms. They are used to identify information in computer systems world-wide.
* In SNOMED CT **universally unique identifiers** is used to uniquely identify reference set members. Since *universally unique identifiers* are unique and it is unnecessary to track the issuing of identifiers for the thousands of reference set members that are needed in some implementations.
* In SNOMED CT release files, *universally unique identifiers* are represented as a string following a standard canonical form - a 36 character string containing 32 hexadecimal digits and four hyphens. The hexadecimal digits are arranged in five groups separated by the hyphens. The first group contains 8 hexadecimal digits, the last group contains 12 and each of the three other groups contains 4. So the overall pattern is 8-4-4-4-12.

#### Example

* ac527bed-9c70-4aad-8fc9-015828b148d9

## Alternatives

* **UUID**

## Related Links

* International Telecommunications Union
  * [Universally Unique Identifiers](https://www.itu.int/en/ITU-T/asn1/Pages/UUID/uuids.aspx)
* Wikipedia
  * [Universally Unique Identifier](https://en.wikipedia.org/wiki/Universally_unique_identifier)

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