FHIR: Identity of patient records

Question

As a HISP, we will be getting patient records from different organizations but would like to key the patient records by userid of our system. We will also be exposing the records for third party app developers via APIs. App developers can query for medical records by our userid. From the spec, identifier property is used for cross referencing across different systems and cannot be used for this purpose. I'm thinking of using Id property with value something like {'ID': 'FFEBED08-29EF-E211-BECC-888C662DF58B', 'Type':'User', 'InstanceID':'56D95BB2-1CE0-4BAB-A946-19FD60C48D76' }, where 'ID' is user's ID and 'InstanceID' is unique identifier of record. Is it acceptable? Or should I use modifierextension for storing our userid?

Here is the use case:

1. For a user A in our system, we may get patient records from hospital X and primary care provider Y.
2. User A can query for medical records, we need to merge the records from both providers and present to the user.
3. Each user has a unique id in our system called userId.
4. Patient records are sent by providers X & Y to us after user A authorize using oAuth flow.
5. Our system now knows that the record is for user A and link it using our system's userId. This helps in user A to get the consolidated view of medical records.

What is the appropriate property to store our system's userId?

Answer 1

Given that the userId is also a patient identifier, I'd just add the user identifier to the patient resource when you make the link