The HL7 data format is the most widely used data standard in the healthcare industry. This standard was designed to enable smooth communication between disparate clinical systems and devices. The most widely used version of HL7 is version 2.x. The website puts the adoption figure in the U.S. at 95 percent.

Although a significant revision took place and version 3 was released to evolve the standard, adoption has been slow, with many vendors still implementing version 2.x in most health IT solutions. HL7 has a distinct message structure that allows developers to compose and send messages about any relevant event such as admission, transfer, discharge, etc.

While these messages are coded in plain text format, they are not easy to interpret by someone who has not been trained to work with them. The following is a brief explanation of the HL7 message standard. We’ll cover its segments and fields and provide an example to illustrate how a simple message is encoded.

HL7 Messages

An HL7 message may be organized into single or multiple segments. By convention, each segment occupies one line of text, and one segment is separated from others by a return character.

HL7 Segments

A segment is the basic subdivision of an HL7 message, and it consists of other units called composites or fields. Each segment of an HL7 message contains a single category of data, such as patient demographic or admission data.

Each segment has a name specified in the initial field of the segment, and it usually consists of three characters. The most common is the message header segment identified by the field “MSH .” The message header contains information about the sender and receiver and the timestamp of the message.

Here’s an example of a message header segment:


The HL7 has more than 120 message types with different header fields. Commonly used segment types include PID for patient personal information and NK1 for next of kin data.

The standard also allows vendors and developers to create custom segments to transmit special information. These segments typically begin with the letter Z.

HL7 Composites

Composites are the building blocks of message segments. Composites are commonly called fields, and the pipe character (|) separates one field from another.

A field may be a string or numeric data type, and it may also contain sub-composites or sub-fields. A further division is the sub-sub-composite, and they are delimited by the caret (^) characters. This last field subdivision is delimited by the “&” symbol.

HL7 Message Types

The HL7 standard specifies hundreds of message types. Some of the most commonly used HL7 message types include:

  • ADT – Admit, discharge, transfer
  • ORM – Order entry
  • MDM – Medical document management
  • ORU – Observation result
  • ACK – Acknowledgement message
  • RDS – Pharmacy/treatment dispense
  • SIU – Scheduling information unsolicited

Integration With the Right HL7 Data Format

HL7 is still the essential data standard for health care interoperability. However, it has challenges, twists, and turns due to “non-standard implementations.”

Let’s Talk About Your HL7 Integration Needs

Contact Lifepoint Informatics at 877.522.8378 today to discuss your integration projects. Visit our contact page to schedule a free consultation and see a demo of our HL7 integration solutions.