Identifier — Qualified identifier
Identifier carries an external identifier with its source system. The system + value pair makes the identifier globally unique.
Purpose
Identifier is used everywhere a resource may be identified by an external id: Patient.identifier, Encounter.identifier, Organization.identifier, Practitioner.identifier. The system field is OID (urn:oid:...) or canonical URL, which qualifies the issuing authority.
Key fields
| Field | Type | Cardinality | Role |
|---|---|---|---|
use | code | 0..1 | usual, official, temp, secondary, old. |
type | CodeableConcept | 0..1 | Identifier type (MR, NI, SS, DL...). |
system | uri | 0..1 | Issuing system URI (urn:oid:... or canonical URL). |
value | string | 0..1 | Identifier value. |
period | Period | 0..1 | Validity period. |
assigner | Reference(Organization) | 0..1 | Assigning organisation. |
JSON example
Acme Healthcare local MRN:
{
"use": "official",
"type": {
"coding": [{
"system": "http://terminology.hl7.org/CodeSystem/v2-0203",
"code": "MR",
"display": "Medical Record Number"
}]
},
"system": "urn:oid:1.2.36.146.595.217.0.1",
"value": "12345",
"period": { "start": "2026-01-01" },
"assigner": { "reference": "Organization/acme-healthcare" }
}Common pitfalls
- system missing: identifier not dedupable. Always qualify.
- OID vs URL: stay consistent — switching between the two on the same identifier breaks FHIR searches.
- type.coding with v2-0203 code: stay on the standard v2-0203 CodeSystem (MR, MA, MC, SS, DL, PI, NI...). Custom codes are non-portable.
Related resources
- Patient.identifier — Patient identifiers (MRN, INS-NIR, etc.).
- NamingSystem — Formal catalogue of system URIs.
- Reference — Reference.identifier allows pointing without a FHIR URL.