What Are HL7 Standards?

Health Level Seven (HL7) refers to a set of international standards designed to streamline the sharing of clinical and administrative data across healthcare systems. These standards ensure that disparate health IT applications can communicate effectively, regardless of the vendors or technologies in use.

HL7 standards function at the application layer (Level 7) of the OSI model, which is responsible for interfacing directly with end-user services. This layer governs data formatting, transmission protocols, and the overall structure of messages.

Why HL7 Matters

• Interoperability: HL7 standards are foundational for achieving interoperability across healthcare systems, enabling seamless data exchange between hospitals, clinics, labs, payers, and public health organizations.
• Efficiency: Standardized data formats reduce the need for manual entry, lowering administrative overhead and minimizing the risk of transcription errors.
• Continuity of Care: Consistent access to accurate patient data leads to better clinical decisions and continuity across care settings.

HL7 is maintained by HL7 International, a not-for-profit organization comprised of healthcare stakeholders worldwide. Since its inception in 1987, HL7 has become the dominant force in health IT messaging standards.

A Brief History of HL7

Understanding the timeline of HL7 development helps contextualize its role in today’s healthcare landscape.

1987: HL7 International Founded

Formed to address the growing need for standardization in the rapidly expanding health IT sector.

1989: HL7 Version 2 Released

HL7 V2 introduced a standardized message format for transmitting patient data. Its flexibility and simplicity led to widespread adoption across hospitals and labs.

2000: CDA (Clinical Document Architecture)

A document standard derived from HL7 Version 3. CDA enabled the sharing of clinical narratives and structured data within a single document.

2005–2010: HL7 Version 3 (V3)

An ambitious attempt to create a more structured and semantically rich standard. Despite its formal modeling approach, it saw limited real-world adoption due to complexity.

2014: HL7 FHIR Introduced

FHIR (Fast Healthcare Interoperability Resources) modernized HL7 by leveraging RESTful APIs and JSON/XML, aligning with contemporary web development practices.

Today, HL7 includes multiple standards (V2, V3, CDA, FHIR), each serving different roles in healthcare data exchange.

Key HL7 Versions and Components

HL7 Version 2 (V2)

HL7 V2 is the most widely implemented healthcare messaging standard globally. It is designed for point-to-point system communication and supports messages related to admissions (ADT), orders (ORM), results (ORU), and billing (DFT).

• Message Structure: Uses delimiters (|, ^) to separate data fields.
• Flexibility: Highly customizable, allowing vendors to create custom Z-segments.
• Challenges: This flexibility can lead to inconsistent implementations and interoperability issues.

HL7 Version 3 (V3)

V3 aimed to resolve V2’s inconsistencies by enforcing a more rigid data model based on a Reference Information Model (RIM).

• Format: XML-based.
• Strength: Semantic interoperability.
• Limitations: Low adoption due to its steep learning curve and implementation complexity.

CDA (Clinical Document Architecture)

CDA is a standard for structured documents that blend narrative text with coded data elements.

• Use Cases: Discharge summaries, referrals, continuity of care documents.
• Adoption: Widely used in Meaningful Use and data exchange programs.

FHIR (Fast Healthcare Interoperability Resources)

FHIR represents the most modern HL7 standard and is designed for real-time data access via APIs.

• Data Format: JSON and XML.
• Transport: RESTful APIs using HTTP(S).
• Modular Design: Composed of “resources” like Patient, Observation, and Encounter.
• Advantages: Developer-friendly, scalable, supports mobile and cloud integration.

How HL7 Facilitates Data Exchange

HL7 standards provide a common language that enables healthcare systems to exchange data reliably and meaningfully.

HL7 V2 Example:

When a patient is admitted:

• ADT^A01 message is sent from the registration system.
• It includes segments such as:
  • MSH: Message header
  • PID: Patient identification
  • PV1: Patient visit
• These messages are routed to lab systems, billing, EHRs, and more.

FHIR Example:

A patient app queries data:

• GET /Patient/123 returns the patient’s demographics in JSON.
• Supports CRUD operations (Create, Read, Update, Delete).
• Real-time queries enable up-to-date insights into a patient’s record.

Interface Engines

Integration engines (e.g., Mirth, Rhapsody) serve as the backbone for HL7 implementations, translating messages, handling errors, and managing connections.

Benefits of Implementing HL7

1. Enhanced Interoperability

HL7 allows disparate systems to exchange structured data without relying on custom integrations, enabling smoother workflows across platforms.

2. Improved Patient Outcomes

By providing real-time access to clinical data, HL7 enables clinicians to make more informed decisions, reducing the likelihood of adverse events.

3. Reduced Administrative Burden

Automated data sharing eliminates repetitive data entry, streamlines documentation, and accelerates billing cycles.

4. Scalability

HL7’s modular approach (especially with FHIR) enables healthcare organizations to adopt new technologies and scale their data infrastructure as needed.

5. Regulatory Compliance

Standards like HL7 FHIR support compliance with ONC’s interoperability rules and initiatives like TEFCA and the 21st Century Cures Act.

Challenges in HL7 Implementation

1. Legacy System Constraints

Many healthcare organizations still operate outdated systems that may not fully support HL7, requiring middleware or costly upgrades.

2. Implementation Variability

Flexible standards can lead to inconsistent implementations. This requires extensive interface mapping and custom development.

3. Technical Expertise

HL7 implementation demands skilled IT professionals familiar with healthcare workflows, message formats, and security protocols.

4. Data Governance

Organizations must define clear policies for data ownership, access control, and audit logging to ensure responsible data exchange.

5. Security & Compliance

HL7 V2 lacks native encryption. Implementers must add secure transport layers (VPN, TLS) and use OAuth2 for FHIR APIs to safeguard patient data.

HL7 vs. FHIR: What’s the Difference?

Feature	HL7 V2	FHIR
Year Introduced	1989	2014
Format	Delimited Text	JSON/XML
Transport	TCP/IP	RESTful APIs (HTTPS)
Ease of Implementation	Moderate to Complex	Developer-Friendly
Best Use Cases	Internal messaging (labs, ADT)	Patient apps, analytics, cloud services

Key Differences:

• HL7 V2 is event-driven and optimized for hospital system integration.
• FHIR is resource-based, supporting modular data exchange ideal for modern applications.
• FHIR leverages internet protocols, making it more accessible for web and mobile developers.

Real-World Use Cases of HL7

Hospitals

ADT messages enable real-time updates across departments, reducing communication lags and ensuring clinical staff has the latest patient information.

Laboratories

Orders (ORM) and results (ORU) flow automatically between lab equipment and EHRs, supporting rapid diagnostics.

Radiology

Imaging orders and reports are transmitted via HL7 to PACS and EHR systems, allowing immediate access to results.

Public Health

Vaccination data (VXU messages) and disease reports are sent to health departments, enabling real-time epidemiological tracking.

Patient-Facing Applications

FHIR APIs allow patients to retrieve their records securely through portals and mobile apps like Apple Health or MyChart.

Health Information Exchanges (HIEs)

HIEs aggregate data from multiple providers using HL7 and FHIR to build longitudinal patient records.

Best Practices for HL7 Implementation

1. Define Clear Integration Goals
   • Identify systems to connect and data types to exchange.
2. Adopt Standard Implementation Guides
   • Use HL7 profiles or national standards (e.g., US Core, IHE).
3. Use Robust Integration Engines
   • Employ tools like Mirth Connect, Corepoint, or Rhapsody for scalable message routing.
4. Focus on Data Quality
   • Ensure clean, accurate, and codified data to support downstream analytics and care decisions.
5. Ensure Security and Compliance
   • Implement TLS, OAuth2, and logging mechanisms. Regularly audit interfaces.
6. Plan for Ongoing Maintenance
   • Monitor message queues, errors, and system changes to ensure stability.
7. Train Teams Continuously
   • Provide clinical and IT staff with ongoing education on new standards and workflows.

The Future of HL7 and Interoperability

1. Widespread FHIR Adoption

FHIR is central to U.S. interoperability mandates, including the 21st Century Cures Act, which requires patient-accessible APIs.

2. TEFCA and National Networks

The Trusted Exchange Framework and Common Agreement (TEFCA) aims to unify health data exchange across the U.S., largely powered by HL7 standards.

3. App Ecosystems and APIs

More EHRs are offering FHIR-based APIs, enabling innovation through SMART on FHIR apps and custom integrations.

4. AI and Big Data

Standardized data via HL7 enables machine learning models and population health tools to function at scale.

5. Global Expansion

Countries like the UK, Canada, Australia, and India are adopting HL7 FHIR in national health IT strategies.

6. Integration with IoT

FHIR extensions support wearables, remote monitoring tools, and connected medical devices for holistic patient views.

Final Thoughts

HL7 standards remain the cornerstone of healthcare interoperability. From HL7 V2’s foundational messaging to FHIR’s modern APIs, each version has played a critical role in transforming healthcare delivery.

For healthcare IT leaders, implementing HL7 isn’t just about connecting systems—it’s about unlocking better care, empowering patients, and future-proofing health IT infrastructure.

Whether you’re integrating internal hospital systems, launching a telehealth platform, or building patient-centered applications, HL7 provides the foundation for efficient, secure, and meaningful data exchange.

FAQs

What does HL7 stand for?
Health Level Seven – referencing the 7th layer of the OSI model (application layer).

Is FHIR part of HL7?
Yes. FHIR is a standard developed by HL7 International.

Is HL7 mandated by law?
In many regions, including the U.S., FHIR-based APIs are mandated for certified EHRs under ONC rules.

Can HL7 be used in mobile apps?
Yes. FHIR is specifically designed for web and mobile integration.