Support for searching for Observation?subject:identifier

[bmilius-nmdp]

According to https://www.hl7.org/fhir/search.html#reference I should be able to search for Observations with a subject where the reference is only an identifier, e.g.,

"subject": {
    "identifer": {
        "system": "http://acme.org/fhir/identifier/mrn",
        "value": "123456"
    }
}

using GET [base]/Observation?subject:identifier=http://acme.org/fhir/identifier/mrn|123456

"The modifier :identifier allows for searching by the identifier rather than the literal reference"

As far as I can tell, this is not supported in HAPI.

We could really use this capability.

[tadgh]

Just checking, does this search work for you? Wondering if chaining resolves this issue or not.

GET [base]/Observation?subject.identifier=http://acme.org/fhir/identifier/mrn|123456

Maybe this can hold you over if it does work, until the :identifier qualifier is implemented.

[bmilius-nmdp]

Thanks, but no. The Patient resource doesn't exist so nothing is returned. We prefer to use the subject.identifier in the Observation so the sender doesn't have to know the reference id when sending us data.

[tadgh]

Understood. Could you do me a favour and provide me some sample observations or other resources you would like to work with which contain this identifier-only reference, in full? This may not be too painful to implement.

[bmilius-nmdp]

{
    "resourceType": "Observation",
    "status": "final",
    "category": [
        {
            "coding": [
                {
                    "system": "http://terminology.hl7.org/CodeSystem/observation-category",
                    "code": "vital-signs",
                    "display": "Vital Signs"
                }
            ],
            "text": "Vital Signs"
        }
    ],
    "code": {
        "coding": [
            {
                "system": "http://loinc.org",
                "code": "9279-1",
                "display": "Respiratory rate"
            }
        ],
        "text": "Respiratory rate"
    },
    "subject": {
        "identifier": {
            "system": "http://example.org/identifier",
            "value": "1234567"
        }
    },
    "effectiveDateTime": "1999-07-02",
    "valueQuantity": {
        "value": 26,
        "unit": "breaths/minute",
        "system": "http://unitsofmeasure.org",
        "code": "/min"
    }
}

[tadgh]

Thanks! I've actually never seen anybody just put a sole identifier in a reference field. TIL this was possible

[bmilius-nmdp]

btw, there's a thread about this on chat.fhir.org https://chat.fhir.org/#narrow/stream/179167-hapi/topic/searching.20for.20subject.3Aidentifier

[tadgh]

This isn't exactly what you are after, but something that may hold you over is using the Auto Create placeholder references by Identifier feature. An example usage is detailed here: https://smilecdr.com/docs/fhir_repository/creating_data.html#auto-create-placeholder-reference-targets-with-identifier. (Sorry for the smile link, it was just the first one i could find). HAPI FHIR supports these settings.

While it won't let you execute your subject:identifier search, what it would do is create a placholder patient with that MRN id, and point the subject to that reference. Then you could search using a chain as normal. Obviously this is non-optimal, but may hold you over until this gets implemented.

[bmilius-nmdp]

Thanks. I'll take a look at it.

[bmilius-nmdp]

Is there an open test HAPI server that has implemented the auto create placeholder? I'd like to play with it without spinning up a test server.

[tadgh]

I have DMed you on zulip with credentials to a box that has this enabled.