“FHIR Compliant” does not mean what you think it means.
Let’s say you want to integrate with a number of different EHRs. Each one claims FHIR compliance and each one has comprehensive API documentation.
You get to work, confident that you can build a single interface to talk FHIR to each EHR.
After all, that’s what FHIR is for, isn’t it?
Same API. Same data model. Same access protocols.
Everything works as expected for the first EHR. It’s the one you spent most of your research time on and it’s the one you built your interface around.
Then you dig into a second and a third EHR and you find that your common interface doesn’t work.
Each EHR exposes and returns different data.
Your “happy path” EHR gives you all the patient and clinical data you need.
Others restrict certain elements in the patient resource, fail to expose Observations of a particular type, or have no support for the key search parameters you planned to use.
And then you encounter the edge-case EHR that implements access control in a unique way, insisting you attach a custom search parameter with your Organization ID as part of each query.
Your common interface module breaks down completely.
You need to build a custom interface for each EHR. You need to handle different or missing data depending on the source. You need to build EHR-specific search queries to work around missing search parameters.
You might as well be talking to custom APIs with proprietary data models.
Yet each of those EHRs is “FHIR compliant.”
What’s going on?
In some countries, “FHIR compliant” can mean complying with specific regulations like ONC certification in the US or EHDS requirements emerging in Europe. These mandate a minimum set of data. They don’t mean ALL data will be the same.
FHIR is intentionally permissive. Most elements are optional, and vendors can choose which search parameters to implement. Beyond regulatory requirements, “FHIR compliance” is not governed or awarded. It’s self-declared, usually by a vendor’s marketing department.
FHIR was designed for flexibility. That very flexibility is why “FHIR compliant” should not give you confidence.
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