HL7, which is an abbreviation of Health Level Seven, is a standard for exchanging information between medical applications. This standard 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. Examples of HL7 messages include patient records, laboratory records and billing information.
The following sections provide an overview of the HL7 standard. The following topics are covered:
- What an HL7 message looks like, and what its components are;
- What versions of the HL7 standard are in use or are under development;
- The acknowledgment (ACK) protocol that indicates that an HL7 message has been successfully received.
Additional sections discuss the advantages and disadvantages of using the HL7 standard and provide technical details of the HL7 standard and its common transport methods. You will not need to read these sections to understand the HL7 standard, but they may be useful to you if you need additional background information to implement your application or interface.
The Name "Health Level-7"
The name "Health Level-7" is a reference to the seventh "application" layer of the ISO OSI Reference model. The name indicates that HL7 focuses on application layer protocols for the health care domain, independent of lower layers. HL7 effectively considers all lower layers merely as tools.[1]
1. Understanding HL7 Messages
This section describes the contents of an HL7 message and how an HL7 message is organized. The following topics are covered:
- The components of an HL7 message;
- The delimiter characters that are used to separate these components;
- How to determine the type of an HL7 message;
- How message segments are organized.
2. Versions of the HL7 Standard
To make it easier to send and receive health-care information, the HL7 organization has defined a standard that specifies what types of HL7 messages can be sent, what segments can be included in these messages, and what fields can be included in their segments.
The HL7 standard is constantly evolving. To date, the HL7 committee has released eight versions of the HL7 standard:
- 2.1
- 2.2
- 2.3
- 2.3.1
- 2.4
- 2.5
- 2.5.1
- 2.6
A revised version of the HL7 standard, version 3.0, has been in ongoing development since 1997, but is not yet in common use.
The following sections provide more information about these versions of the HL7 standard.
3. The ACKnowledgment Protocol
An important part of the HL7 standard is the ACKnowledgment protocol. Every time an application accepts a message and consumes the message data, it is expected to send an ACKnowledgment message back to the sending application. The sending application is expected to keep on sending a message until it has received an ACK message.
An acknowledgment message consists of two segments:
- An MSH segment, which contains information about the sending and receiving applications and contains the Message Control ID of the message;
- An MSA segment, which indicates whether the message was accepted or rejected.
4. Advantages and Disadvantages of HL7
This section will discuss the advantages and disadvantages of HL7 by taking a closer look at open systems (HL7) vs. closed systems (proprietary interface model) and the pros and cons of each model. You will also learn about the advantages of using cost-effective HL7 tools and why HL7 is not simply plug-and-play.
5. HL7 Technical Details
The following sections provide more detailed technical information related to the HL7 standard. These sections cover the following topics:
- The protocol characteristics of the HL7 standard;
- The most common transport methods for HL7 messages.
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