HL7v2 vs. FHIR: Navigating the Transition

If you’ve ever worked with healthcare IT systems in the UK, chances are you’ve come across HL7v2 messages—even if you didn’t realise it. For decades, HL7 version 2 has been the workhorse of healthcare interoperability. From sending lab results to moving patient admissions data between hospital systems, HL7v2 has been quietly powering NHS IT infrastructure since the 1980s.

But now, there’s a new player in town: FHIR (Fast Healthcare Interoperability Resources). It’s modern, web-based, and API-friendly—the kind of technology that feels more at home in today’s digital-first world. The big question many people in the UK healthcare sector are asking is: what happens when HL7v2 meets FHIR? Are we replacing the old with the new, or are they going to coexist for years to come?

Let’s unpack that together.

A quick refresher: what is HL7v2?

HL7v2 (or just HL7) is one of the oldest and most widely used healthcare messaging standards in the world. It was first released in 1989, and believe it or not, a huge amount of the NHS still depends on it.

Think of HL7v2 as a courier that delivers simple text-based messages between systems:

A hospital sends a message that a patient has been admitted (an “ADT” message).
A lab system sends back a test result (“ORU” message).
A pharmacy system sends medication details.

The beauty of HL7v2 is its simplicity and efficiency. It’s lightweight, it works, and it’s proven. But it also has some serious limitations:

It’s not always human-readable.
Messages can vary by vendor, making interoperability messy.
It’s not designed for modern APIs, mobile apps, or cloud-native systems.

In short: HL7v2 is dependable, but it belongs to a different era of healthcare IT.

And then comes FHIR

Now let’s look at FHIR, which has taken the healthcare world by storm since HL7 released it in 2014. If HL7v2 is the old-school courier, FHIR is the sleek, modern digital platform.

FHIR uses web standards like REST, JSON, and XML—the same ones that power apps, smartphones, and online services we all use every day. Instead of sending long text-based messages, FHIR provides structured resources—modular building blocks for patients, allergies, medications, observations, and more.

What makes FHIR so appealing is its developer-friendly design. If you’re building a healthcare app in the UK today, you don’t have to learn obscure HL7v2 syntax. You can just use RESTful APIs, exactly the way you’d build a modern web app.

So why the shift from HL7v2 to FHIR?

For the NHS and UK healthcare organisations, the shift is about much more than technology—it’s about strategy and future-proofing.

Interoperability across Integrated Care Systems (ICSs): ICSs demand seamless data sharing across GPs, hospitals, community, and social care. FHIR, with its modular design, is a better fit for this than HL7v2.
Patient-facing services: Apps like the NHS App rely on APIs. You can’t easily build patient-friendly mobile apps with HL7v2 messages, but you can with FHIR.
Innovation ecosystem: The UK healthtech sector thrives on startups and developers. FHIR lowers the barrier to entry for innovation because it speaks the same language as modern developers.
Global alignment: Countries across Europe, the US, and beyond are standardising on FHIR. The UK doesn’t want to be left behind.

But here’s the reality: HL7v2 isn’t going anywhere (yet)

It’s tempting to imagine FHIR swooping in and replacing HL7v2 overnight. But anyone who’s worked in healthcare IT knows it doesn’t work like that.

Why?

Legacy systems: NHS Trusts have decades of investment in HL7v2-based systems. You don’t just rip those out.
Reliability: HL7v2 is fast and efficient for high-volume messaging (like lab results). It’s not broken—so why fix it?
Cost of transition: Moving thousands of systems to FHIR would be enormously expensive and disruptive.

That’s why many experts believe we’re entering a long period of coexistence where HL7v2 and FHIR work side by side.

How does the transition look in practice?

Here’s how it’s unfolding in the UK:

Bridging technologies: Many vendors are building HL7v2-to-FHIR translators. That way, older systems can keep sending HL7v2, but newer systems and apps can consume FHIR APIs.
FHIR-first NHS initiatives: National programmes, like the NHS API platform and GP Connect, are being built directly on FHIR.
Laboratory and pathology systems: These are still heavily HL7v2-driven, but pilots are underway to migrate certain workflows to FHIR.
Procurement contracts: New NHS tenders increasingly specify FHIR compliance. Vendors that can’t deliver it will struggle to stay relevant.

So the reality is: HL7v2 is the backbone of today, and FHIR is the roadmap for tomorrow.

What does this mean for professionals?

If you’re a healthcare IT professional in the UK, here’s what you need to know:

Learn both: HL7v2 knowledge isn’t obsolete—it’s still essential. But add FHIR literacy to your skillset if you want to stay relevant.
Focus on integration: Expect hybrid environments where you’re bridging HL7v2 and FHIR for years.
Understand the use cases: HL7v2 may remain dominant in labs, while FHIR takes over patient apps, ICS-level data sharing, and research platforms.
Be aware of policy shifts: NHS England’s emphasis on open standards and FHIR compliance means that procurement and funding will increasingly favour FHIR.

Common misconceptions about HL7v2 and FHIR

“HL7v2 is dead.”

Not true. It’s still the backbone of many NHS systems, especially in hospitals and labs.

“FHIR can do everything HL7v2 does, but better.”

Not exactly. FHIR is more flexible and modern, but HL7v2 is extremely efficient for high-volume transactional data. Both have strengths.

“The NHS will flip a switch to FHIR.”

Nope. This is a gradual, evolutionary transition, not a revolution. Expect coexistence for at least another decade.

Looking ahead: the future of the transition

Over the next 5–10 years, here’s what I think we’ll see in the UK:

National FHIR mandates: NHS England will increasingly require new digital services to be FHIR-compliant.
Modernisation of core hospital systems: As legacy systems are replaced, vendors will deliver FHIR-native solutions.
Expansion of APIs: More patient- and clinician-facing apps powered by FHIR will emerge.
Gradual retirement of HL7v2 in some areas: Especially where APIs and analytics are more important than transactional speed.

The key word here is gradual. HL7v2 has earned its place through decades of reliability, and it won’t vanish overnight. But the centre of gravity is definitely shifting towards FHIR.

Wrapping up

So, HL7v2 vs. FHIR isn’t really a battle. It’s more like a relay race. HL7v2 carried the baton for decades, ensuring that healthcare systems in the UK could exchange critical information. Now, FHIR is reaching out for that baton, ready to take us into a future of open APIs, patient empowerment, and innovation.

For professionals, the trick is to stop thinking of HL7v2 and FHIR as competitors. Instead, think of them as partners in transition. HL7v2 keeps the current system running; FHIR builds the future. And for a long time, they’ll both be part of the NHS’s digital story.

So, the next time someone asks, “Are we moving from HL7v2 to FHIR?” you can confidently say: We’re not just moving—we’re bridging, coexisting, and gradually transforming. That’s the real picture.