Element Uses the Wrong Coding System
A profile requires a specific code system (for example LOINC for lab codes or SNOMED CT for clinical findings). The Coding or CodeableConcept uses a different system URI or none.
FHIR · Error
The error
must use a specific coding system but uses anotherWhy it happens
Coding the value with a local or proprietary system, or omitting the system entirely so the code is ambiguous.
How to fix it
Use the required system URI on the coding. For lab observation codes that is http://loinc.org; for many clinical concepts it is http://snomed.info/sct. Include the matching code from that system.
Example
The snippet below triggers the error:
{
"resourceType": "Observation",
"status": "final",
"code": { "coding": [{ "system": "http://hospital.local/labcodes", "code": "GLU" }] }
}The corrected version:
{
"resourceType": "Observation",
"status": "final",
"code": { "coding": [{ "system": "http://loinc.org", "code": "2345-7", "display": "Glucose" }] }
}Frequently asked questions
Can I include both a local code and the required system?
Yes. A CodeableConcept may carry multiple codings. Include the required system (for example LOINC) so it conforms, and you may add your local coding alongside it for traceability.