Has anyone had any experience of doing this in the UK?
I’m working for new style regional diagnostics organisation (name will be NHS NW Genomics from April) - we will need to extend the data models in both HL7 v2 and FHIR for enterprise rather than point to point use.
I believe we are the first to attempt this in the UK (xlabs/npex may have done so for laboratory), so not expecting many/any answers 
I’m starting with EPIC as it has quite good documentation (and a local NHS Trust is using EPIC as it’s EPR). Will be wanting to move onto meditech afterwards.
The proposed change is being worked on but can be found here Correlation Identifier - NHS North West Genomics v0.1.0
This relates to FHIR Identifiers and V2 EI and CX datatypes - I’m calling it a data contract as it crosses standards (and also spread into IHE XDS).