What is HL7? (Health Level Seven)
Healthcare systems don’t naturally speak the same language. A hospital’s EHR, a lab system, a pharmacy platform, and a billing tool are often built by different vendors, on different technologies, at different times. HL7 is the standard that makes them talk to each other.
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Definition of HL7
HL7, which stands for Health Level Seven, is a set of international standards for the exchange, integration, sharing, and retrieval of electronic health information. The “Level Seven” refers to the seventh layer of the ISO OSI (Open Systems Interconnection) model — the application layer — which is the layer concerned with how software applications communicate with each other.
Founded in 1987, HL7 International is the nonprofit organization that develops and maintains these standards. Today, HL7 standards are used in healthcare facilities across 55+ countries, making it one of the most widely adopted frameworks in health IT.
In simple terms: HL7 defines the format and structure of messages that healthcare systems use to share patient data.
How HL7 Works in Healthcare
HL7 works by defining a common language — a messaging format — that different healthcare systems can use to send and receive data. Think of it like a universal translator sitting between two systems that otherwise wouldn’t understand each other.
When a patient is admitted to a hospital, for example, the admissions system generates an HL7 message and sends it to the EHR, the billing system, the lab system, and the pharmacy — all at the same time. Each system reads the same structured message and updates its own records accordingly.
This happens through a series of HL7 message types, each designed for a specific event:
- ADT messages (Admit, Discharge, Transfer) — track patient movements
- ORM messages (Order) — communicate clinical orders like lab tests or medications
- ORU messages (Observation Result) — send lab results back to ordering providers
- MDM messages (Medical Document Management) — handle clinical documents like discharge summaries
- SIU messages (Scheduling Information Unsolicited) — manage appointment data
Each message is broken into segments (like rows in a table) and fields (like columns), separated by specific delimiters. A receiving system knows exactly where to find each piece of data based on the position defined by the HL7 standard.
Key HL7 Standards and Specifications
HL7 is not a single standard — it is a family of standards. The most important ones you’ll encounter in healthcare IT are:
HL7 Version 2 (HL7v2)
The most widely deployed HL7 standard in the world. Despite being decades old, HL7v2 still powers the majority of hospital interfaces today. It uses a pipe-delimited text format and is highly flexible — which has also been its biggest challenge, since implementations can vary significantly between organizations.
HL7 Version 3 (HL7v3)
An XML-based standard designed to be more rigorous and consistent than v2. While technically more precise, HL7v3 was complex to implement and saw limited adoption compared to v2.
CDA (Clinical Document Architecture)
Built on HL7v3, CDA is a document markup standard for clinical documents such as discharge summaries, progress notes, and referral letters. It defines both the structure and the semantics of a clinical document.
FHIR (Fast Healthcare Interoperability Resources)
The newest and fastest-growing HL7 standard. FHIR uses modern web technologies (REST APIs, JSON, XML) to make healthcare data exchange faster and more developer-friendly. FHIR is now mandated by CMS and ONC for patient data access. It is increasingly replacing older HL7 interfaces for new development.
Implementation Considerations
Implementing HL7 in a healthcare environment is rarely straightforward. Here are the key considerations:
Interface engines are almost always required. Systems like Mirth Connect, Rhapsody, or Iguana act as middleware — receiving HL7 messages from one system, transforming them as needed, and routing them to the destination system. Without an interface engine, each point-to-point connection requires custom development.
HL7v2 has significant variability. The standard is flexible by design, which means two organizations implementing the same HL7 message type can do it differently. This is often called the “HL7 dialect” problem — a message from Hospital A may need transformation before Hospital B can understand it.
Testing is non-negotiable. HL7 integration failures can result in missing lab results, incorrect patient records, or failed medication orders. Thorough testing in a sandbox environment before go-live is essential.
FHIR is the future. While HL7v2 remains dominant in legacy environments, all new interoperability requirements from CMS and ONC are FHIR-based. Organizations should plan their roadmap accordingly — maintaining existing HL7v2 interfaces while building new capabilities on FHIR.
Security and compliance matter. HL7 messages contain PHI (Protected Health Information). All HL7 interfaces must be secured in transit (TLS encryption) and access must be controlled and audited to meet HIPAA requirements.
How Taction Helps with HL7
At Taction, our engineering team has deep hands-on experience building and maintaining HL7 integrations across a wide range of healthcare settings — from community hospitals to large health systems, payers, and digital health platforms.
What we do:
- HL7 interface development — We build custom HL7 interfaces for ADT, ORM, ORU, MDM, and other message types, tailored to your specific EHR and operational needs.
- Interface engine configuration — We configure and manage Mirth Connect and other interface engines, handling message transformation, routing, and error management.
- HL7v2 to FHIR migration — We help organizations transition from legacy HL7v2 interfaces to modern FHIR APIs, reducing technical debt while maintaining continuity of operations.
- EHR integration — We have experience integrating with Epic, Cerner, MEDITECH, Allscripts, and other major EHR platforms using both HL7v2 and FHIR.
- HIPAA-compliant architecture — All integrations we build are designed with security and compliance built in from day one, not bolted on afterward.
Whether you’re building a new integration from scratch, troubleshooting a broken interface, or planning a broader interoperability strategy, our team can help you move faster with fewer surprises.
Related Terms and Resources
Explore related glossary terms:
- What is FHIR? — The modern replacement for many HL7v2 interfaces
- What is ADT? — One of the most common HL7 message types
- What is CDA? — The HL7 standard for clinical documents
- What is EHR? — The systems HL7 most commonly connects
- What is HIE? — Health Information Exchanges that rely on HL7
Helpful resources:
- HL7 International — Official standards body
- Download the Healthcare IT Glossary PDF — All 55 terms in one document (CTA: gated download)
Ready to build or modernize your HL7 integrations? Taction’s healthcare integration engineers are available to assess your current interfaces, identify gaps, and build a roadmap for scalable, compliant data exchange.