> 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                                                                               |
| --------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------ |
| <p>AllergyIntolerance.code</p><p><br></p><p><br></p><p><br></p> | <p>If recording is based on substances and products and specifies the type of reaction in "type":</p><p><<105590001</p>  |
| AllergyIntolerance.code                                         | <p>If recording is based on finding concepts precoordinating the type of reaction :</p><p><<418038007</p>                |
| AllergyIntolerance.code                                         | <p>When using precoordinated Situation concepts to represent the absence of an allergic propensity</p><p><<716186003</p> |
| AllergyIntolerance. reaction.substance                          | <<105590001                                                                                                              |
| AllergyIntolerance. reaction.manifestation                      | <<404684003                                                                                                              |
| AllergyIntolerance. reaction.exposureRoute                      | <<284009009                                                                                                              |

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