FHIR-Compliant Is the Starting Line, Not the Finish Line

The compliance claim

“We’re FHIR-compliant.”

I hear this a lot. And I’ve learned to gently push back on it.

Anyone who has spent significant time connecting health systems learns this the hard way: two systems can both be fully FHIR-compliant and still fail to exchange a single useful thing.

That sounds like a contradiction, but it isn’t.

FHIR is a toolkit, not a rulebook

Think of FHIR as English.

Two people can both speak it fluently and still not understand each other. One gives an address as a street and house number. The other says, “the blue gate past the market.” Both are correct. Neither system can act on the other’s answer.

That’s FHIR: a toolkit, not a rulebook. It gives you the vocabulary and grammar, then leaves enormous freedom in how you use them.

So “we both use FHIR” promises far less than it sounds. Real interoperability doesn’t come from adopting the standard. It comes from constraining it.

Agree on the rules

An Implementation Guide is the national rulebook: for this country and this workflow, use these fields, these formats and these code lists. Not “record the diagnosis somehow,” but “record it here, this way, from this list.”

But a rulebook on paper changes nothing. Everyone nods in the meeting, then quietly goes and builds their own version anyway. If you’ve ever led an integration, you’re smiling right now.

Prove conformance

What actually makes it work is conformance: a sandbox where systems prove they follow the rules before they connect, and validation that rejects bad data before it pollutes the shared record.

Without that, your guide is just a suggestion.

Interoperability isn’t a document you publish. It’s a contract you enforce.

Ask what “FHIR-compliant” means

If you’re funding or leading this work, one habit can save you a lot of money. The next time a vendor says they’re “FHIR-compliant,” treat it as the starting line, not the finish.

Then ask two questions:

• Compliant with which national Implementation Guide?
• Who’s testing that they actually conform?

Get those right, and systems genuinely talk. Skip them, and you’ve bought a very expensive vocabulary that still says different things.

Adopting the standard was never the hard part. Agreeing on what it means and proving we did is the work that actually connects us.