> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.cail.health/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.cail.health/_mcp/server.

# FHIR R4 in CAIL Health

CAIL Health models every clinical resource as [FHIR R4](https://hl7.org/fhir/R4/). If a payload represents an organization, a location, a clinical pathway, a patient response, an observation, or an aggregate metric, it conforms to the corresponding FHIR R4 resource shape.

## Resources you will see

The most common FHIR resource types in API requests and responses:

| Resource                | Used for                                     |
| ----------------------- | -------------------------------------------- |
| `Organization`          | Health boards and providers                  |
| `Location`              | Physical and virtual care locations          |
| `HealthcareService`     | Services a provider offers                   |
| `Endpoint`              | Integration endpoints for a provider         |
| `Schedule` and `Slot`   | Provider availability                        |
| `Questionnaire`         | The question set used during navigation      |
| `QuestionnaireResponse` | A patient's answers during pathway traversal |
| `PlanDefinition`        | A versioned clinical decision tree           |
| `Encounter`             | Clinical encounters                          |
| `Observation`           | Clinical measurements and wait-time signals  |
| `Communication`         | Alert messages routed to subscribers         |
| `MeasureReport`         | Aggregate metrics for reporting              |

## Coding systems and regional terminology

FHIR coding values come from one of two sources:

* **Standard systems** (LOINC, SNOMED, ICD-10, RxNorm) where the resource has a canonical international coding.
* **Jurisdiction-specific systems** for terminology that differs by region, including risk tier codes, provider taxonomy, and wait-time metric codes.

When a value is jurisdiction-specific, the active jurisdiction's coding is used. See [Jurisdictions](/concepts/jurisdictions) for how the active jurisdiction is determined.

## What is not exchanged in FHIR

Authentication tokens, pagination metadata, alert thresholds, and error envelopes are CAIL-specific contracts, not FHIR resources. See [Auth model](/concepts/auth-model), [Pagination](/reference/pagination), and [Error envelope](/reference/error-envelope).