Coding and Identification Scheme Object Identifiers (OIDs)

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Introduction to OIDs

HL7 uses OIDs (Object Identifiers) to identify coding schemes and identification schemes.

OIDs are strings of numbers separated by dots. Each number indicates a branch from in a tree of identifiers. The first set of branches is allocated by ISO and further levels nationally and by other organisations. Therefore OIDs can be allocated by any organisation with a unique OID root from which to allocate branches. Provided each organisation respects the need for uniqueness in its allocation of branches the resulting OID will uniquely identify an object.

The object identified by an OID could be anything. For example, HL7 allocates OIDs for message components as well as coding and identification schemes. However, for the purposes of this page we are primarily concerned with the use of OIDs for identifying two types of object:

  • A coding scheme or terminology (e.g. OCS Specialty Codes, Read Codes, SNOMED CT)
    • The OID goes in the codeSystem attribute of an instance of an HL7 Version 3 coded datatype (CD, CE, CV) in which the code attribute is a code from the specified scheme.
    • In some cases, the OID may be included as a fixed attribute in the message specification rather than with each instance.
  • An external scheme of identifiers (e.g. NHS Numbers, GP Numbers, Referral Numbers)
    • The OID goes in the root attribute of the instance identifier datatype (II) with the actual identifier in the extension attribute.
    • In the case of instance identifier that do not refer to an external coding scheme the root may represent the entire identifier and may either be an OID or a UUID/GUID and there is no need for an extension attribute.

For a full list of the types of objects HL7 UK allocates OID for please consult the HL7 UK OID management policy.

A single message can use OIDs from various sources and a single scheme can be identified by more than one OID (e.g. by an OID from more than one organisation). Once issued, an OID is never withdrawn and always identifies the same scheme or object.

To assist UK projects using HL7 messages that require OIDs for coding and identification schemes HL7 UK has registered OIDs for some coding and identification schemes in widespread use in the NHS.

For instructions on how to request a new OID or register an existing one please consult the HL7 UK OID management policy and Main Branches of HL7 UK OIDs.


OIDs are mandatory for use with HL7 Version 3, and with some IHE profiles. HL7 FHIR can still use OIDs, but it is now preferred to use more meaningful URI based identifiers. HL7 UK maintains a registry of identifier systems used with FHIR here.

OID roots for HL7 and HL7 UK

The HL7 Branch OID is 2.16.840.1.113883
External Identification schemes registered with HL7 2.16.840.1.113883.4
Internal Coding schemes registered with HL7 2.16.840.1.113883.5
External Coding schemes registered with HL7 2.16.840.1.113883.6
The HL7 UK Branch OID is 2.16.840.1.113883.2.1
External Identification schemes registered with HL7 UK 2.16.840.1.113883.2.1.4
External Coding schemes registered with HL7 UK 2.16.840.1.113883.2.1.6

Main HL7 OID Registry

The main registry for HL7 international OIDs can be found here.

HL7 UK registered OIDs

Allocation of an OID does not imply any statement of quality about the scheme registered. The OID merely identifies the scheme. Inclusion of an OID in these lists does not imply a right to access the associated coding scheme data which in many case is associated with copyright or privacy restrictions.

Please note that OID Registration is FREE for HL7 UK Members, there is a charge of £150 + VAT for Non-members.

HL7 International registered OIDs relevant to the UK

This is only a selection of OIDs known to be of immediate use in the UK NHS.
For a full list please go to the HL7 OID registry.
You will then be able to query the register and download PDF or XML representations as necessary.

OID CodingSystemName Description Issuer
2.16.840.1.113883.5.1001 ActMood Act mood code; as specified by the Version 3 Data Types specification. HL7
2.16.840.1.113883.5.110 RoleClass HL7 Role Class codes HL7
2.16.840.1.113883.5.14 ActStatus HL7 Act Status codes HL7
2.16.840.1.113883.5.89 ParticipationSignature HL7 Participation Signature codes HL7
2.16.840.1.113883.6.28 The Read Codes 4 Byte Set See also OID 2.16.840.1.113883. National Health Service (UK)
2.16.840.1.113883.6.29 The Read Codes Version 2 The Read Codes Version 2

See also OID 2.16.840.1.113883.

National Health Service (UK)
2.16.840.1.113883.6.6 NHS Clinical Terms Version 3 (Read Codes) NHS Clinical Terms Version 3 Codes National Health Service (UK)
2.16.840.1.113883.6.3 ICD10 International Classification of Diseases 10th Edition World Health Organisation
2.16.840.1.113883.6.96 SNOMED CT SNOMED codes College of American Pathologists