> ## Documentation Index
> Fetch the complete documentation index at: https://docs.junction.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Choosing Tests and Markers

> Choose saved lab tests, à la carte markers, or a combination of both when defining what a lab order should include.

Use the `order_set` field when you [create an order](/api-reference/lab-testing/create-order) to define the tests and markers the laboratory should perform. You can reference reusable lab tests, select markers directly from the [compendium](/lab/overview/compendium-search), or combine both approaches.

| Approach                    | Use when                                                        |
| --------------------------- | --------------------------------------------------------------- |
| One saved lab test          | You repeatedly order a predefined set of markers.               |
| Multiple saved lab tests    | You need to combine compatible saved definitions for one order. |
| À la carte markers          | You need a one-off selection without creating a saved lab test. |
| Saved lab test with add-ons | You need a standard definition plus patient-specific markers.   |

## Understand tests and markers

### Markers

[Markers](/api-reference/lab-testing/biomarkers) are the individual items a partner laboratory makes available to order. A marker can represent a single biomarker or a laboratory-defined panel. For example, Junction represents both a vitamin D test and a lipid panel as markers.

### Lab tests

[Lab tests](/lab/workflow/create-test) are reusable definitions that contain one or more markers. Create a lab test when your program repeatedly orders the same combination. When you place an order, reference the lab test's `id` in `order_set.lab_test_ids`.

## Choose what to order

Choose the `order_set` combination that matches how your integration manages reusable test definitions.

### Use one saved lab test

Reference one previously created lab test when the same marker set is used repeatedly:

<CodeGroup>
  ```python Python theme={null}
  from junction import Junction, OrderSetRequest
  from junction.environment import JunctionEnvironment

  client = Junction(
      api_key="YOUR_API_KEY",
      environment=JunctionEnvironment.SANDBOX,
  )

  client.lab_tests.create_order(
      order_set=OrderSetRequest(
          lab_test_ids=["<lab_test_id>"],
      ),
      # ...
  )
  ```
</CodeGroup>

### Combine saved lab tests

Reference two or more compatible lab tests when you want to combine their markers without creating another reusable definition:

<CodeGroup>
  ```python Python theme={null}
  from junction import Junction, OrderSetRequest
  from junction.environment import JunctionEnvironment

  client = Junction(
      api_key="YOUR_API_KEY",
      environment=JunctionEnvironment.SANDBOX,
  )

  client.lab_tests.create_order(
      order_set=OrderSetRequest(
          lab_test_ids=["<lab_test_id_1>", "<lab_test_id_2>"],
      ),
      # ...
  )
  ```
</CodeGroup>

### Choose markers à la carte

Use à la carte ordering to select markers from the compendium without first creating a lab test.

<Note>
  À la carte ordering is generally available to all Teams, but not every marker supports it. See [Find markers available à la carte](#find-markers-available-à-la-carte).
</Note>

Identify the markers with either Junction `marker_ids` or the partner laboratory's `provider_ids`. Do not provide both identifier types in the same `add_on` object.

<CodeGroup>
  ```python Python theme={null}
  from junction import AddOnOrder, Junction, LabTestCollectionMethod, OrderSetRequest
  from junction.environment import JunctionEnvironment

  client = Junction(
      api_key="YOUR_API_KEY",
      environment=JunctionEnvironment.SANDBOX,
  )

  client.lab_tests.create_order(
      order_set=OrderSetRequest(
          add_on=AddOnOrder(
              provider_ids=["322022"],
              # marker_ids=[1],
          ),
      ),
      collection_method=LabTestCollectionMethod.WALK_IN_TEST,
      # ...
  )
  ```
</CodeGroup>

### Add markers to a saved lab test

Use `add_on` with `lab_test_ids` when an order needs a reusable lab test plus patient-specific markers.

<CodeGroup>
  ```python Python theme={null}
  from junction import AddOnOrder, Junction, LabTestCollectionMethod, OrderSetRequest
  from junction.environment import JunctionEnvironment

  client = Junction(
      api_key="YOUR_API_KEY",
      environment=JunctionEnvironment.SANDBOX,
  )

  client.lab_tests.create_order(
      order_set=OrderSetRequest(
          lab_test_ids=["<lab_test_id>"],
          add_on=AddOnOrder(
              provider_ids=["322022"],
              # marker_ids=[1],
          ),
      ),
      collection_method=LabTestCollectionMethod.WALK_IN_TEST,
      # ...
  )
  ```
</CodeGroup>

<Note>
  When you provide `add_on`, you must also provide `collection_method`.
</Note>

## Choose a collection method

Junction supports four collection methods: [Mobile Phlebotomy](/lab/at-home-phlebotomy/overview), [Walk-in](/lab/walk-in/overview), [At-home Test Kits](/lab/testkits/overview), and [On-site Collection](/lab/on-site-collection/overview).

The collection method can come from the saved lab test or from `collection_method` in the order request. Provide it in the order request when the selected lab tests do not resolve to one collection method or when using `add_on`.

<CodeGroup>
  ```python Python theme={null}
  from junction import Junction, LabTestCollectionMethod, OrderSetRequest
  from junction.environment import JunctionEnvironment

  client = Junction(
      api_key="YOUR_API_KEY",
      environment=JunctionEnvironment.SANDBOX,
  )

  client.lab_tests.create_order(
      order_set=OrderSetRequest(
          lab_test_ids=["<lab_test_id>"],
      ),
      collection_method=LabTestCollectionMethod.WALK_IN_TEST,
      # ...
  )
  ```
</CodeGroup>

#### At-Home Phlebotomy Auto-Approval

<Card horizontal icon="person-digging" color="#57164A">
  This feature is in **closed beta**.

  Interested in this feature? Get in touch with your Customer Success Manager.
</Card>

This beta applies only to auto-approval of at-home phlebotomy tests. When ordering without a *Lab Test*, this is subject to the same auto-approval validation as `POST /v3/lab_tests`. For eligible teams and labs, this validation is successful when:

* Collection Instructions are available for every marker.
* Every marker is enabled for *à la carte* ordering, if your team does not use a delegated flow.
* The estimated draw is fewer than 15 tubes. An estimate of 15 tubes or more is rejected.

A referenced lab test must be `active`. A pending at-home phlebotomy test that was created before auto-evaluation applied to the current team can return HTTP 400 when ordered.

## Find markers available à la carte

Not every marker can be ordered à la carte. Use [Get Markers](/api-reference/lab-testing/biomarkers) with the `a_la_carte_enabled` filter to find supported markers.

<CodeGroup>
  ```python Python theme={null}
  from junction import Junction
  from junction.environment import JunctionEnvironment

  client = Junction(
      api_key="YOUR_API_KEY",
      environment=JunctionEnvironment.SANDBOX,
  )

  markers = client.lab_tests.get_markers(
      name="322022",
      a_la_carte_enabled=True,
  )

  if not all(m.a_la_carte_enabled for m in markers.markers):
      raise Exception("Markers not a_la_carte_enabled")
  ```
</CodeGroup>

## Test-selection errors

The API validates the selected tests, markers, laboratories, and collection methods before accepting an order.

### 400 Bad Request

* `collection_method must be set if add_on is set`: Include `collection_method` whenever you provide `add_on`.
* `marker_ids or provider_ids must be set in add_on`: Include one marker identifier type in `add_on`.
* `cannot set both marker_ids and provider_ids in add_on`: Use either Junction marker IDs or provider IDs, not both.
* `cannot order lab_tests from multiple labs`: All referenced lab tests must belong to the same partner laboratory.
* `cannot order lab tests with multiple collection methods`: Provide one compatible `collection_method` when combining lab tests.
* `test is not active`: A referenced lab test is still pending approval or otherwise inactive. It cannot be ordered until its status is `active`.

## Related guides

* [Creating a Lab Test](/lab/workflow/create-test)
* [Compendium Search](/lab/overview/compendium-search)
* [Orders and Results](/lab/overview/orders-and-results)
* [Create Order](/api-reference/lab-testing/create-order)


## Related topics

- [API](/changelog/lab-testing/api.md)
- [Deprecations](/changelog/lab-testing/deprecations.md)
- [Introduction](/lab/overview/introduction.md)
- [Get Markers for Lab Test](/api-reference/lab-testing/lab-test-markers.md)
- [Get Markers for Order Set](/api-reference/lab-testing/order-set-marker.md)