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HL7 FHIR vs HL7 v2 and v3: Com...

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HL7 FHIR vs HL7 v2 and v3: Comparing Healthcare Interoperability Standards

HL7 FHIR vs HL7 v2 and v3: Comparing Healthcare Interoperability Standards
The Silicon Review
22 July, 2024

Today's Healthcare organizations must efficiently exchange patient health information across a wide range of care settings. To enable such health data interoperability, the Health Level 7 (HL7) global standards body has developed versions 2, 3 and the latest Fast Healthcare Interoperability Resources (FHIR) specifications. This article examines the key features, differences and use cases for HL7 v2, v3 and FHIR standards.

Introduction to HL7 Standards

HL7 refers to a set of international standards for the transfer of clinical and administrative data between healthcare computer systems and applications. These HL7 integration standards focus on interfaces, messaging structure, and meaning to allow independent health information systems to communicate with each other seamlessly.

The core HL7 standards include:

  1. HL7 v2 - The widely adopted messaging standard that has been in use since 1987.
  2. HL7 v3 - An XML-based messaging standard designed as a next-generation upgrade to v2.
  3. FHIR - The latest interoperability specification based on modern web standards and architectural patterns.

HL7 v2: The Longstanding Messaging Standard

HL7 version 2, commonly called v2, provides specifications for electronic messaging and data exchange between healthcare applications. Introduced in 1987, it remains the most commonly used HL7 standard globally.

Key Features and Capabilities

  • Defines message structures and data types for clinical, financial, and administrative transactions.
  • Uses delimited flat file encoding, which is easy to parse.
  • Supports point-to-point messaging, store and forward processing using queues and publish-subscribe distribution.
  • It covers a wide range of use cases, including admissions, discharge and transfer (ADT), orders, results, billing, etc.

Benefits and Limitations

HL7 v2 has served the healthcare industry well over the last 3+ decades. It will continue to have mainstream adoption in the future due to:

Benefits

  • Ubiquitous deployment and tooling support
  • Lightweight and fast transactions
  • Backward compatibility support across minor version upgrades

Limitations

  • Proprietary customizations reduce out-of-box interoperability
  • Tight system coupling makes exchange with new systems harder
  • Weak data typing allows variability in message interpretation

Use Cases

Some common use cases where HL7 v2 excels include:

  • Real-time order entry and results delivery
  • Clinical documentation and physician notes
  • Registration, scheduling, and billing
  • Public health reporting and population health
  • Legacy system integration and data exchange

HL7 v2 is best suited for simple point-to-point data transactions between known systems rather than enterprise-wide information exchange.

HL7 v3: The Next-Generation XML-based Standard

HL7 version 3, commonly called v3, was designed in the late 1990s to replace v2 messaging. It provides an XML-based standard for representing, sharing, and integrating health information across systems.

Key Features and Capabilities

  • Formal information models ensuring semantic interoperability
  • XML encoding allows validation against message schemas
  • Supports document-centric exchange and service-oriented interactions
  • Role-based access control and security specifications

Benefits and Limitations

HL7 v3 was envisioned to address the limitations around flexibility and interoperability with v2. But it failed to replace v2 due to:

Benefits

  • Stronger data typing and semantic definitions
  • Enterprise-level master patient index (MPI) and terminology services capabilities
  • Building block approach allowing reusable specifications

Limitations

  • The steep learning curve for implementers familiar with v2
  • Performance overhead of XML messaging and parsing
  • Limited backward compatibility support

Use Cases

Some scenarios where HL7 v3 provides better support compared to v2 include:

  • Regional health information exchange (HIE) and electronic health record (EHR) systems
  • Standardized clinical decision support and order sets
  • Clinical research systems and semantic data analysis
  • Reference information model integration
  • Master patient index management
  • Healthcare analytics and reporting

However, v3 adoption has been gradual and niche compared to the popularity of v2.

HL7 FHIR: The Modern API-based Standard

Fast Healthcare Interoperability Resources (FHIR) is the newest HL7 standard for health data exchange, introduced in 2014. It leverages modern web standards and architectural paradigms. Companies such as Langate help businesses integrate all the standards compliantly.

Key Features and Capabilities

  • RESTful API framework with JSON/XML payload support
  • Atom and JSON feed support for notification of data changes
  • Pluggable security protocols like SMART on FHIR and OAuth 2.0
  • Built-in analytics support and bulk data access capabilities
  • Extensive core resource library with terminology binding

Benefits and Limitations

FHIR is positioning itself as the next-generation interoperability standard based on multiple strengths:

Benefits

  • Developer-friendly API framework and ecosystem
  • Lightweight and high-performance
  • Platform and language neutrality
  • Clinical terminology alignment
  • Data modeling built on v3 and other standards

Limitations

  • Additional tooling and distribution infrastructure requirements
  • Compliance and certification processes are still maturing
  • Limited legacy system support as of now

Use Cases

Some key scenarios where FHIR shines include:

  • Mobile health applications and patient engagement platforms
  • Healthcare IoT integration and clinical genomics data exchange
  • Cloud-based storage for EHR and health information exchange
  • AI and ML-driven solutions for precision medicine
  • Public API access to population health datasets

According to the data, the majority, or 84% of hospitals and 61% of clinicians, adopted and implemented certified API technology that was FHIR-enabled. This implies that health data can flow using the data standard and that third-party developers can connect to these providers' EHRs using standardized FHIR APIs.

Comparing HL7 v2, v3 and FHIR

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The below table summarizes some key aspects of the three HL7 standards:

 

Standard

Initial Release

Encoding

Tooling

Use Cases

Adoption Level

HL7 v2

1987

Delimited / Pipe representation of message segments

Mature and widely available

Real-time healthcare delivery

+++++ High

HL7 v3

2005

XML schema representation

Niche availability

Healthcare analytics and research

++ Low

HL7 FHIR

2014

JSON/XML REST API

Growing ecosystem support

Mobile health apps and patient engagement

+++ Fast growth

Let us examine some specific differences across data structure, architecture, and key functionality support:

Data Structure and Grammar

  • v2 has terse and cryptic data element names; weak data typing allows variability in interpretation
  • v3 has strongly typed hierarchical message schemas described in UML with formal semantics
  • FHIR has a strongly typed but lightweight schema with customizable extensions

Architecture Paradigm

  • v2 supports point-to-point messaging exchange between systems
  • v3 enables document-centric exchange with some service-oriented capabilities
  • FHIR is based on a modern web API architectural style

Key Feature Support

  1. v2 has limited structured vocabulary and terminology binding
  2. v3 enables rich semantic alignment using reference models
  3. FHIR balances semantics and approachability via the terminology layer
  4. v2 lacks formal security exchange protocols
  5. v3 defines security models but complex to implement
  6. FHIR provides pluggable OAuth2 profiles for authentication
  7. v2 has minimal metadata definitions for data sources
  8. v3 provides mature provenance, attribution, and audit trail capabilities
  9. FHIR has basic support for healthcare provenance assurance

Choosing the Right HL7 Standard

Each of the three HL7 standards has its strengths and applications.

HL7 v2 is the right choice when:

  • You need simple and fast data exchange with legacy systems
  • Investment protection is critical for previously integrated applications
  • Tightly coupled point-to-point transactions are sufficient

HL7 v3 delivers the best value when:

  • Semantic interoperability is highly critical
  • Enterprise master data management capabilities are required
  • Advanced security, privacy, and governance protocols are needed

HL7 FHIR is the modern standard to embrace for:

  • Developing new solutions and greenfield integrations
  • Exposing data and services to a broader range of applications
  • Analyzing population health data and clinical genomics research
  • Building patient-centered solutions for engagement

The Road Ahead for Healthcare Interoperability Standards

While HL7 v2 will retain mainstream relevance in the healthcare ecosystem in the years ahead, future growth and innovation will be driven by FHIR adoption. The HL7 standards body is also working on a consolidated CDA on FHIR specification that combines the strengths of v3 and FHIR.

As healthcare continues its trajectory towards value-based coordinated care models, securely exchanging structured patient information across a diverse set of old and new systems becomes paramount. This is where modern interoperability standards like FHIR will be vital for the vision of seamless health data exchange.

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