Is FHIR R4 Different Than FHIR?

Some services say that they use FHIR, while others proudly announce their use of FHIR R4. But for most people, FHIR and FHIR R4 are the same thing! That’s because FHIR R4 is simply “Release #4” - the name for the most recent version of the Fast Healthcare Interoperability Resources (FHIR) specification.

FHIR R4 has been the latest stable version of FHIR since 2019. A service that relies on FHIR R4 is based on the latest stable edition of the FHIR standard. Looking for R4 instead of FHIR is like trying to find the difference between Windows and Windows 11.

The vast majority of FHIR implementations in use today use FHIR R4, which was the first normative release of FHIR. There are many legacy systems in healthcare, so it’s possible for implementers to encounter a different version of FHIR. However, if you’re implementing FHIR in a production environment, then FHIR and FHIR R4 are probably one and the same.

Does Particle Use FHIR R4?

Particle’s API supports FHIR R4! It’s safe to say that FHIR is our favorite technology. We encourage healthcare organizations to build with it. 

That’s not all our platform does. We support the USCDI v1 data elements; and we also share healthcare data in the C-CDA format. These are interesting components of health tech, but FHIR is the future.

‍What Makes R4 Normative?

As a normative standard, FHIR R4 signaled that certain resource types among the FHIR architecture had reached a stable state. Normative status entails trying to ensure forward compatibility with future releases according to the version management policy of HL7 (the standards organization overseeing FHIR). Previous FHIR releases were titled FHIR STU 1-3, as they only rose to the level of a Draft Standard for Trial Use.

While FHIR continues to evolve, “applications based on FHIR R4 will have a long life cycle and greater portability,” Vanderbilt professor Russell Leftwich, MD said when R4 was finalized. Similarly, Cerner’s SVP of medical informatics explained R4 implementers can rest assured that resources are “guaranteed not to change, at least for a well-specified and extended period." 

The health IT industry coalesced around FHIR R4 as a standard for health information exchange after it was published in October 2019. Not only did this happen at the start of a high demand era for digital health, it also coincided with US government rulemaking for the Cures Act. The Cures Act had codified FHIR APIs a part of healthcare policy, and regulators at this time determined that FHIR R4 was the version that counted, leading to FHIR R4’s dominant market share.

“Anything that becomes part of a federally-approved standard should have a certain degree of stability and market ecosystem support,” Micky Tripathi - now the government’s chief interoperability expert - said at the time, “and normative approval is an indicator of that.”

When Can We Expect FHIR R5, and What’s In It?

Updates to the FHIR format are continually under development. HL7 has been remarkably transparent with its roadmap for those who want to follow it.

• FHIR R5 Release Date: In 2019, FHIR product director Graham Grieve predicted that FHIR R5 would launch in Q3 2020. “Our normal [release] cycle is about 20 months,” he added. Understandably, COVID derailed these plans. FHIR R5 is far from complete, and Grieve recently changed his FHIR R5 release date target to 2023 at the earliest.

• FHIR R5 Changes: Developers agreed to finalize developed versions of FHIR resources, which are the building blocks of the FHIR format. Popular resources like AllergyIntolerance and Practitioner have seen enough successful real-world use to be upgraded to a greater “maturity” level, meaning that fewer changes are expected. A new “implementation guide” resource would be launched for the first time as well.

• FHIR R4B: Even as FHIR R5 development continues, FHIR R4B may bridge the gap between releases. It’s intended to be fully compatible with R4 except for “new and revised resources … in the areas of medication regulation and evidence based medicine” that is “urgently required by certain communities, including FDA, EU and Canadian drug agencies”. While FHIR R4B is likely to come out before R5, it’s unclear when that will happen.

When we talk about FHIR (in early 2022), we generally mean FHIR R4. It’s still the hottest version of FHIR around!