HL7 – The Health Information Technology Standard


HL7 is an abbreviation of Health Level Seven, it is a standard for exchanging information between medical applications. It defines a format for the transmission of health-related information. Information sent using the HL7 standard is sent as a collection of one or more messages, each of which transmits one record or item of health-related information. HL7 messages include patient records, laboratory records and billing information. Although HL7 and their messages are widely used, many systems don’t know how to speak the language and require a translator. HL7 interface engines work alongside existing applications as an interpreter, speaking the language of HL7.

HL7 Messages are used to transfer electronic data between disparate healthcare systems. Each HL7 message sends information about a particular event such as a patient admission. An HL7 message consists of one or more segments. Each segment consists of one or more composites, also known as fields.

An important part of the HL7 standard is the Acknowledgement (ACK) Protocol. Every time an application accepts a message and consumes the message data, it is expected to send an Acknowledgement (ACK) message back to the sending application. The sending application is expected to keep on sending a message until it has received an ACK message.

The Technical Details

• Protocol Characteristics

1. Event-Driven
Real-world events, such as the admission of a patient, cause messages to flow between applications. In other words, an application that encounters a real-world event sends a message to other applications that need to be aware of this event.

2. Application-to-Application
HL7 defines a communication between two independent applications, rather than between closely coupled, client/server applications. The scope of interest for HL7 is the message exchange between the applications, rather than the specific role of each application in the healthcare delivery process.

3. Point-to-Point
HL7 is a messaging format that is independent of its transport method. However, it is typically used in a client/server environment for employing some form of a point-to-point protocol. For instance, HL7 can use the LLP Transport method to transfer messages between a client and a server. However, since a client must establish a connection to a server before a message can be sent, the client must have prior knowledge about the server. It is not normal for HL7 messages to use a non point-to-point protocol, where the client listens for ‘broadcasts’ from a particular server.

4. OSI Level 7
OSI Level 7 indicates that HL7’s scope is the format and content of the data exchanged between the applications rather than how the messages are transmitted between computers or networks. In other words, HL7 does not specify how messages will be delivered between the applications. Usually a TCP/IP connection or FTP file transfer is used to deliver a message. However, within local area networks, the de facto standard is the Lower Layer Transport Protocol.

5. Data Exchange
HL7 specifies the way data exchange between applications will be accomplished. It does not specify how applications store or process this data. It would be advantageous for an application developer if their application’s database structure coincided with HL7 message definitions, but this is not mandatory.

6. Standard
When you create a proprietary, non-standard link between two systems, you can create a message exchange system that better suits your personal needs and better fits the data structure of your application. However, the efforts invested in this link are useless when considering a connection to other third-party systems. Using HL7 means that your initial development effort can be reused again and again.

7. Common HL7 Transports
– LLP Lower Layer Protocol
– TCP/IP Basics
– Client or Server
– Testing TCP/IP Server Connections
– Hybrid Lower Layer Protocol

• HL7 Interface

There are several types of roles involved with HL7 interfaces, including clinical application analysts, integration specialists, application programmers, and systems analysts.

To facilitate communication between two healthcare applications, a modest HL7 Interface includes:

– An export endpoint for the sending application
– An import endpoint for the receiving application
– A method of moving data between the two endpoints
– A method for handling the queuing messages
– A method for logging the flow of messages.

Logic tells us that each healthcare application must grant access to accept and send patient data and have rules of what it will accept and what it will send. Frequently, the access grant will be hard-and-fast rules rather than flexible ones that provide easy methods for exchanging data. This access to data is usually tightly controlled by each application vendor to ensure data integrity within their application. To implement an HL7 interface between two or more applications, providers usually implement either a point-to-point interfacing approach or utilize an interface engine.

As an active participant in the development of healthcare related systems Ranosys Technologies has implemented the HL7 standards in its projects. An HL7 work effort represents an activity being undertaken by an existing work group or board appointed committee to achieve specific objectives or to product specific work products.

HL7 recognizes that the work efforts have grown to a level of complexity that require more formal project management approaches that include, but are not limited to, proper scope definition with timelines, identification of dependencies and prerequisites, project management tools, and project management staffing to guide larger projects and coordinate across projects. Ranosys Technologies focuses on all these crucial points and the implementation is applied to our projects so that they are compliant with the global norms.