---
title: FHIR Request Parameters
slug: medhistory-populations/guide/fhir-request-parameters
docTags:
createdAt: 2026-07-24T17:07:26.906Z
---
This section outlines common FHIR parameters that customers may use in their requests. To view the full capabilities of Surescripts Medication History for Populations, retrieve the **CapabilityStatement** resource from the FHIR API.
:::hint{type="info"}
**Note: **See the Messages Overview section for details on how search requests are processed on the back end of your organization’s system.
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| **Parameter** | **Requirement** | **Description** | **Example** |
| --------------------- | --------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------- |
| \_lastUpdated | optional | Indicates the date time of search request.
Use **gt** to indicate greater than and **lt** for less than to define the loopback window of the request.
Format must be *YYYY-MM-ddTHH\:mm\:ssZ* (in UTC)
**Note:** You may use a smaller lookback window (e.g., last 4 hours or 1 day) when generating panels or notifications. The maximum allowable lookback period is **one month** from the requested date. | - \_lastUpdated=gt2026-09-15T11:00:00Z
- \_lastUpdated=lt2026-09-15T15:00:00Z |
| \_include | optional | Identifies resource to be returned in your response.
**include\:iterate** must be used for resources beyond the 1st resource requested. | * \_include=Communication\:based-on
* \_include=MedicationDispense.prescription
* \_include\:iterate=MedicationRequest\:requester |
| \_revinclude | optional | Identifies resource to be returned in your response by performing a reverse reference lookup.
**include\:iterate** must be used for resources beyond the 1st resource requested. | revinclude=Condition\:subject
**Note:** This looks up Condition resources based on the subject (Patient resource). |
| \_page\_token | conditional | Indicates which page of results to retrieve. Defaults to **1** if not provided. **Required** when additional pages are available. The next page’s token is supplied in Bundle.link. | \_page\_token= Ad86NARb\_Wb3LSoymHxmqiNWoxEs5Lc5MLHnKI48YRUCE58IC2KYqMET |
| \_count | optional | Size of page that will contain the matches of MedicationDispenses Defaulted to 50 if not populated. Max is 1000. | \_count=50 |
| \[parameter]\:missing | optional | The missing modifier used with a parameter will filter FHIR search results include/exclude results don’t have an associated value.
* **True** = Values exist
* **False** = Values don’t exist
**Note:** This can be used to exclude patient results where the patient was not found. | based-on\:missing=false |