HL7 v2 — The Standard That Refuses to Retire
A 1987 pipe-delimited format still carrying most real-time hospital messages.
What HL7 Actually Is — and Why It Matters
HL7 is a family of standards, not one — name which one.
HL7 v3 — Important to Know, Limited in Practice
An XML replacement that never caught on; survives as the basis for C-CDA.
FHIR — The Modern Standard
The modern REST/JSON standard; FHIR R4 is mandated in the U.S. under ONC.
C-CDA — For Structured Clinical Documents
The mandated U.S. format for structured clinical document exchange.
The Practical Reality for 2026
Hospital builds hit all three: v2 events, FHIR R4 APIs, C-CDA documents.
When to Use Which Standard
A practical decision framework for choosing between HL7 v2, FHIR, and C-CDA based on use case, integration target, and data requirements.
Use HL7 v2 for Real-Time Event-Based Clinical Notifications
ADT, labs, radiology, pharmacy orders and scheduling all flow as HL7 v2 through hospital interface engines.
Use FHIR for On-Demand Data Queries and EHR Write-Back
FHIR R4 is right for on-demand patient queries, ONC-mandated EHR APIs and standardized write-back.
Use C-CDA for Structured Clinical Document Exchange
C-CDA is the ONC-mandated format for care summaries, discharge summaries, referral notes and care plans.
Most Hospital Integrations Require All Three
Hospital products need v2 for real-time events, FHIR R4 for queries and C-CDA for documents.
The Specific Confusions That Break Integrations
Six confusion patterns that appear repeatedly in digital health development — and how each translates directly into expensive integration rework.
Most Expensive
Assuming FHIR Has Replaced HL7 v2
Real-time clinical data still flows via HL7 v2.
Versions Matter
Treating FHIR as a Single Standard
R4 is mandated; profiles differ per guide.
False Signals
Conflating Interface Engines with FHIR Servers
Mirth-style FHIR layers need real validation.
Document Exchange
Forgetting C-CDA for Document Workflows
C-CDA is the mandated clinical document format.
Geography
Applying U.S. FHIR Profiles Internationally
U.S. Core conformance is not Canadian or EU.
Authorization
Underestimating OAuth and SMART on FHIR Complexity
SMART on FHIR OAuth flows are deceptively complex.
The Four Standards Every Digital Health Team Needs to Understand
Plain-language definitions — what each standard is and where it belongs in your integration.
HL7 v2 — Real-Time Clinical Messaging
Pipe-delimited messaging for ADT and labs.
FHIR R4 — Modern REST API for Clinical Data
REST and JSON, mandated for U.S. EHRs.
C-CDA — Structured Clinical Documents
ONC-mandated format for clinical documents.
HL7 v3 / CDA — Know It, Do Not Build New Things on It
Legacy XML standard sitting behind C-CDA.
Building a Healthcare Integration and Need to Get the Standards Right?
Our engineers have shipped across the full HL7 v2, FHIR R4, and C-CDA stack for clinical environments in the U.S. and Canada — from new integration architecture to untangling one built on misunderstood foundations.
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Frequently Asked Questions
[ 1 ]
If FHIR is so much better than HL7 v2, why has v2 not been replaced?
Interface engines and HIS configurations built on HL7 v2 represent decades of investment. FHIR grows fast for new integrations, but teams need both.
[ 2 ]
Is FHIR the same everywhere in the world?
The FHIR base standard is consistent, but U.S. Core, Canadian Core and EU guides differ. R4 compliance in one country is not compliance in another.
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