a nursing informatics toolbox

The Anatomy and Physiology of an HL7 Message

Posted on December 13, 2012 by Rolando Cabral • 21168 Comments

the anatomy of an hl7 message

If you are an Informatics Nurse, I am absolutely sure that in one way or another, the word “HL7” has already crossed your path. Our current Health Information Technology setup is primarily running on the backbone of this revolutionary technology as it enables our disparate systems to communicate using the same language. You might not be working directly on it but I am 100% certain that you, at least, need to be familiar with its basic structure and functions to carry out your tasks.

What is HL7 ?

HL7 (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.

Here is an example of a basic HL7 message:

hl7 message

An HL7 message is composed of sequentially organized segments of information. It includes MSH,EVN,PID,PV1,AL1,DG1 and PR1. The MSH segment serves as the message header that reflects the message type, version and other relevant information.

Each message has a type that defines its purpose. This message has the type ADT^A01 (Patient Admit/Visit notification) of the version 2.4. ( visit Hl7 website for more information)

Each segment starts with a 3 letter abbreviation/label that identifies its message type. In the example below, take note of MSH,EVN,PID,PV1,AL1,DG1,PR1. MSH is the message header, EVN denotes the event. PID contains the patient identification. PV1 is patient visit details. DG1 is diagnosis information and PR1 reflects the procedure performed.

Each segments is divided into fields separated by a pipe character (|). In the example below, it shows that the segment PID is composed of 10 fields with some fields missing.

Fields are further divided into sub fields which are separated by a caret (^) character as shown below.

Understanding HL7 messages is a challenging task. It is, however, one of the most common source of error in any Healthcare IT environment. Aside from “downtime” issues, a missing information through the HL7 interface, is one of the most common problem that I encounter in my current and past assignments. That is why, a nursing informatics professional, in any capacity, should learn to decipher these sometimes cryptic bowl of alphanumeric soup.

Hl7 is a vast concept. It will take years for you to master all its nuances. Understanding, however, its most basic structure and function is the proverbial “first step” towards a journey of a million miles.

For more information about HL7, visit its website at www.hl7.org

watch out for my next tutorial on how to understand HL7 messages, the easy way.

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