> 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/implementation-guides/allergy-implementation-guide/5-implementation-considerations/5.3-terminology-services.md).
# Terminology Services
The recommended approach for implementing SNOMED CT in clinical systems is using standard Terminology Services. HL7 FHIR provides the [CodeSystem](https://build.fhir.org/codesystem.html), [Valuesets](https://build.fhir.org/valueset.html), and [ConceptMaps](https://build.fhir.org/conceptmap.html) resources and their corresponding operations to support access to terminologies using a standardized approach.
These are some examples of how FHIR Terminology services can be used to resolve the terminology bindings described in this guide. using a demo FHIR terminology server:
| FHIR element | FHIR Terminology Services Expand Operation |
| --------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------ |
| AllergyIntolerance.code
| If recording is based on substances and products and specifies the type of reaction in "type":
<<105590001
|
| AllergyIntolerance.code | If recording is based on finding concepts precoordinating the type of reaction :
<<418038007
|
| AllergyIntolerance.code | When using precoordinated Situation concepts to represent the absence of an allergic propensity
<<716186003
|
| AllergyIntolerance. reaction.substance | <<105590001 |
| AllergyIntolerance. reaction.manifestation | <<404684003 |
| AllergyIntolerance. reaction.exposureRoute | <<284009009 |
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