Large standard terminologies like [**SNOMED CT**](https://www.snomed.org/what-is-snomed-ct) (350k+ codes) and [**LOINC**](https://loinc.org/about/) (100k+ codes) are too large to manage within a single FHIR resource. The `$import` operation bulk-loads codes, display names, and metadata into a CodeSystem, enabling you to work with these essential terminologies efficiently.

## Use Cases

- **Loading standard terminologies**: Import SNOMED CT, LOINC, RxNorm, or ICD code systems into your Medplum instance
- **Custom code system management**: Create and populate organization-specific code systems for internal coding standards
- **Terminology updates**: Incrementally add new codes or update metadata when new terminology versions are released
- **Migration and synchronization**: Import codes from existing terminology servers or legacy systems

```text
[baseUrl]/CodeSystem/$import

[baseUrl]/CodeSystem/[id]/$import
```

Privileged Operation

This operation is only available to Project Admins and Super Admins.

## Parameters

| Name | Type | Description | Required |
| --- | --- | --- | --- |
| `system` | `uri` | The canonical URL of the code system to import into | No* |
| `concept` | `Coding` | A code, along with optional display text to add to the code system | No |
| `property` | `Part[]` (see below) | Metadata about codes in the code system to be imported | No |
| `designation` | `Part[]` (see below) | Additional synonyms or translations of codes' display text | No |

note
* If `system` is not provided, the operation must be invoked on a specific `CodeSystem` instance by ID.

Each `property` parameter contains a `part` array with three nested parameters:

| Name | Type | Description | Required |
| --- | --- | --- | --- |
| `code` | `code` | The code to which the property applies | Yes |
| `property` | `code` | The property name (from `CodeSystem.property.code`) | Yes |
| `value` | `string` | The value of the property | Yes |

Any `designation` parameters have three nested `part` parameters:

| Name | Type | Description | Required |
| --- | --- | --- | --- |
| `code` | `code` | The code to which the synonym or translation applies | Yes |
| `language` | `code` | The [language code](https://developer.mozilla.org/en-US/docs/Glossary/BCP_47_language_tag) for translations | No |
| `value` | `string` | Display string | Yes |

Batch size

Each invocation of the `$import` operation can send a maximum of 1,000 of each parameter at a time, e.g. importing 1,000 concepts with one property and one designation each per request.

## Output

The operation returns the `CodeSystem` resource representing the code system into which the given concepts and properties were imported.

## Examples

**Request**:

```ts
const result = await medplum.post(medplum.fhirUrl('CodeSystem', '$import').toString(), {
  resourceType: 'Parameters',
  parameter: [
    { name: 'system', valueUri: 'http://example.com/local-codes' },
    { name: 'concept', valueCoding: { code: 'VS', display: 'Vital signs' } },
    { name: 'concept', valueCoding: { code: 'HR', display: 'Heart rate' } },
    {
      name: 'property',
      part: [
        { name: 'code', valueCode: 'VS' },
        { name: 'property', valueCode: 'child' },
        { name: 'value', valueString: 'HR' },
      ],
    },
    {
      name: 'property',
      part: [
        { name: 'code', valueCode: 'HR' },
        { name: 'property', valueCode: 'units' },
        { name: 'value', valueString: 'bpm' },
      ],
    },
  ],
});
```