FHIR Terminology Service

Requests the server to expand a ValueSet into a flat list of its constituent concepts. This operation resolves all logical and compositional definitions—including intensional rules referencing other value sets—into an explicit enumeration of codes and displays.

• Key Parameter: url or valueSet identifies the set to expand.
• Pagination: Supports offset and count for large expansions.
• Designation: Can include language translations and usage contexts.
• Use Case: Populating a clinician-facing pick-list with all valid LOINC codes for a specific panel.

Validates that a specific code exists within a specified ValueSet and returns its properties. This is the primary mechanism for enforcing terminology binding strength at runtime, ensuring that data conforms to defined constraints.

• Modes: Can validate a code/system pair or a full Coding/CodeableConcept.
• Display Validation: Optionally checks if the supplied display text matches the official term.
• Result: Returns result: true/false with an error message on failure.
• Use Case: Verifying that '116154003' is a valid SNOMED CT code for 'Patient' before submission.

Retrieves the detailed properties and designations for a single concept given its system and code. This operation is essential for displaying human-readable information about a coded element without needing to process the entire code system.

• Properties: Returns version, abstract status, and custom properties like parent or child.
• Designations: Fetches display terms for specific languages and use contexts.
• Reverse Lookup: Can search by a property value to find the associated code.
• Use Case: Displaying the full SNOMED CT hierarchy path for a diagnosis code.

Tests the subsumption relationship between two concepts within the same code system. It determines if one concept is a more general or more specific form of another, enabling hierarchical reasoning over clinical terminologies.

• Outcomes: Returns equivalent, subsumes, subsumed-by, or not-subsumed.
• Transitive Closure: The server handles the full hierarchical chain.
• Code System: Requires both codes to belong to the same system.
• Use Case: Checking if 'Type II Diabetes Mellitus' (44054006) is a child of 'Diabetes Mellitus' (73211009) for cohort identification.

Translates a concept from one code system to another using a ConceptMap resource. This operation handles the semantic mapping between disparate terminologies, such as converting a local proprietary code to a standard SNOMED CT or ICD-10-CM concept.

• Dependency Resolution: Can automatically invoke $translate on mapped dependencies.
• Equivalence: Returns the mapping grade, from equivalent to unmatched.
• Reversibility: Supports translation in the reverse direction if the map is defined.
• Use Case: Converting a legacy lab system's internal code for 'Hemoglobin A1c' to the standard LOINC code 4548-4.

Maintains a persistent, client-specific transitive closure table on the server. The client iteratively provides new subsumption relationships, and the server returns the complete, re-computed closure, enabling efficient offline hierarchical reasoning without re-downloading the entire code system.

• Stateful: Requires a name to identify the closure table.
• Iterative: Clients call it repeatedly with new concepts to build the table.
• Versioning: The server tracks the version of the closure state.
• Use Case: Building a local index of all descendants of 'Cardiovascular Disease' for a clinical decision support rule.

A FHIR resource that formally defines a terminology, enumerating all valid concepts and their associated codes. It serves as the source of truth for a code set.

• Defines the canonical URL that globally identifies the system
• Specifies properties like hierarchy (is-a relationships) and designations (synonyms)
• Examples: SNOMED CT (http://snomed.info/sct), LOINC (http://loinc.org), RxNorm
• A Terminology Service uses this to resolve display names and validate membership

A curated set of codes drawn from one or more CodeSystems, defining the allowed values for a specific data element. It represents a business rule for code selection.

• Can be defined intensionally (e.g., "all codes descending from concept X") or extensionally (an explicit list)
• The Terminology Service performs ValueSet expansion ($expand) to resolve the full list of valid codes at runtime
• Critical for binding a FHIR element like Observation.code to a constrained set of LOINC codes

A FHIR resource that specifies a semantic mapping between concepts in a source CodeSystem and a target CodeSystem. It enables terminology translation.

• Maps can be equivalent, wider, narrower, or unmatched
• The Terminology Service uses the $translate operation to convert a code from one system to another
• Essential for migrating from legacy code systems (e.g., ICD-9 to ICD-10) or harmonizing lab codes to LOINC

The core Terminology Service operation that checks whether a supplied code is valid within a given ValueSet or CodeSystem. It returns a true/false result with detailed error messages.

• Validates the code, system, and optional display text for correctness
• Can test membership in a ValueSet by logical identifier or by providing the ValueSet inline
• Returns an OperationOutcome with issues like code-not-found or display-mismatch

Tests the hierarchical relationship between two concepts within a CodeSystem. It determines if one concept subsumes (is an ancestor of) another.

• Returns subsumes, subsumed-by, equivalent, or not-subsumed
• Relies on the CodeSystem's defined hierarchy property
• Critical for clinical decision support: "Does this SNOMED CT diagnosis code fall under the broader category of 'Cardiovascular Disease'?"

Retrieves the full details for a specific concept from a CodeSystem, including its display name, designations (synonyms), and properties.

• Returns the human-readable display for a raw code
• Can request specific language translations for designations
• Used to populate user interfaces with the correct clinical term when only a code is stored
• Example: Looking up 267036007 in SNOMED CT returns "Dyspnea" with synonyms like "Breathlessness"