Searching Hierarchies

[alexandre-guimond]

I'm interested in searching for Patients managed by an Organization or any of its sub-Organizations (partOf). FHIR defines the :below modifier that allows to do this :

{{fhirurl}}/Patient?organization:below=someid

But it seems the Azure FHIR Service (R4) does not support the :below modifier for searching hierarchies (i.e. using references). This isn't specifically stated in the Azure FHIR Service documentation, but I've tried and get the following error:

{
    "resourceType": "OperationOutcome",
    "id": "xxx",
    "meta": {
        "lastUpdated": "2025-03-26T13:29:28.5132095+00:00"
    },
    "issue": [
        {
            "severity": "error",
            "code": "invalid",
            "diagnostics": "Modifier 'Below' is not supported for search parameter 'organization'."
        }
    ]
}

Is there a workaround to achieve a similar result to using :below? Or does anyone know if this is meant to be supported in the near future?

[evachen96]

Hi @alexandre-guimond - are you using the OSS FHIR server, or the managed service FHIR server? The :below modifier is not supported today, can you elaborate on the need for the use case? Have you looked into using referenced searches with custom filtering?

[alexandre-guimond]

Hello @evachen96,

I'm using the Azure FHIR service.

I have considered building a custom search parameter to filter the relevant reference attribute. However, I haven't found a way to traverse hierarchies as the :below and :above modifiers do, aside from using multiple FHIR queries, which generates significant overhead.

Regarding the use case, our product supports multiple customers/organizations with persistent data stored in a single FHIR service. Customers/organizations are represented by hierarchies (using the partOf attribute), e.g., Trust A > Hospital B > Service C > Department D, etc. To limit data access to users of different organizations (hospitals, services, etc.) based on their roles (PractitionerRoles), we need to modify inbound search queries coming from applications (we do this in the Azure API Management service based on claims in the request token). Examples include finding devices owned by, or observations fulfilling requests from, a specific service (including its departments and any sub-organizations):

{{fhirurl}}/Device?organization:below=serviceId
{{fhirurl}}/Observation?based-on:ServiceRequest.requester:below=Organization/serviceId

Our application also allows "read" access to data associated with a "parent" organization. The :above modifier would be useful here.

[evachen96]

Hi @alexandre-guimond - Are you using the OSS, or managed service Azure FHIR service?

We will add this to our backlog, thank you for sharing the information and your use case!

[alexandre-guimond]

Hi @evachen96. I'm using the managed service Azure FHIR service.

[evachen96]

@alexandre-guimond Thanks for the info!

[evachen96]

Internal tracking #151074