8 common questions about HL7

Interoperability: the 'ultimate IT goal of the modern healthcare system'
By Michelle McNickle
12:41 PM
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As recent talks have Health Level Seven International (HL7) moving beyond IT professionals, the standards process is setting the stage to make a significant impact on usability and workflow. And as more communities are embracing HL7, learning the basic ins-and-outs of the standards process is more important than ever. 

Rob Brull, product manager at Corepoint Health, answers eight common questions about HL7. 

1. What is HL7? Interoperability, or the back-and-forth exchange of patient health data among different organizations, is seen as the "ultimate IT goal of the modern healthcare system," when discussing meaningful use, HITECH and the Affordable Care Act, said Brull. "One of the major challenges to healthcare interoperability is defining common standards for structured content of healthcare data and the transport of that data between different systems, created by different vendors," he said. Creating consensus behind a common healthcare standard is the mission of HL7, which was founded in 1987. "The HL7 Standard was created and has since become widely adopted by vendors worldwide to define content," said Brull. 

2. What is the difference between HL7 version 2 and HL7 version 3? According to Brull, HL7 version 3 (v3) isn't all that similar to HL7 version 2 (v2). "While v2 provides a 'negotiated framework' for developers to easily use and adapt, v3 was targeted to be a stricter standard that aimed to eliminate variances, in an effort to improve interoperability between all users of the standard," he said. From a technical standpoint, he added, typical HL7 structure data uses "pipes" (|) and "hats" (^), while HL7 v3 is based on XML. "Due to a large embedded v2 base, adoption of v3 is still very slow in the U.S., with [more than] 90 percent of systems and applications still using some form of HL7 v2," he said. HL7 v3 includes both messages and documents, he added, with v3 documents being called CDA, or clinical document architecture. "While a move to v3 message doesn't appear to be on the horizon, CDA documents have been adopted in meaningful use standards for both Stages 1 and 2," Brull said.  

[See also: HL7 CEO unveils big plans for standards organization.]

3. What are Z segments? Z segments contain clinical or patient data that may not be a good fit for other segments of the HL7 v2 standard, said Brull. "Essentially, it's used as the 'catch all' for data that doesn't fit into the HL7 Standard message definitions – Z segments can be inserted into any message." They're also one reason why the HL7 Standard is sometimes called a "flexible standard," he added. "There literally are no limits to the data contained in a Z segment, or in the number of Z segments included in an HL7 message," said Brull. 

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4. What is an ADT message? The most commonly used HL7 v2 messaging type is ADT, or admit discharge transfer messages, which record patient demographic and visit information. They're typically initiated by the Hospital Information Systems (HIS), or a registration application, said Brull. They also "inform other connected systems about key patient information, such as [when] the patient has been admitted, discharged, transferred, or if the patient's demographic data has changed," such as their name, insurance, or next of kin, he said. 

5. What is an ORM message? According to Brull, ORM messages are general order messages that contain any request for clinical materials such as, for example, 500 ml of saline, or services like an EKG study. "Order messages are usually associated with a particular patient, but they can also be used by a department to order materials," he said. "The transmission of ORM messages occurs between the application placing the order, and the clinical application filling the order." Typically, he added, the caregiver enters an order in the HIS application. This then acts as the "placer" application. "The system that receives the message fro the HIS application is typically considered the 'filler' of the order," Brull said. 

[See also: HL7 offers standard for clinical research in an EHR.]

6. What is an ORU message? ORUs, or observational report messages, are usually the result message from the "filler" application of the ORM message, said Brull. They typically contain information and analysis from medical procedures, like test results from the lab or the radiology department. "ORU messages also can be used for linking orders and results to clinical trails," he added. 

7. What are HL7 separator characters? "Separator characters in HL7 are also known as message delimiters or special encoding characters," said Brull. "The separator characters are defined at the beginning of the HL7 message in the MSH segment." An example MSH segment with the HL7-recommended separator characters would begin: MSH|^~\&, with the separator characters defined as:

  • | (field separator, aka pipe)
  • ^ (component separator, aka hat)
  • & (sub-component separator)
  •  ~ (field repeat separator)
  • \ (escape character)

"While the above separator characters are recommended, the separator character for segments, (ASCII 13 or HEX 0D), is not negotiable," added Brull. 

8. What are HL7 escape sequences? HL7 defined character sequences to represent "special" characters not otherwise permitted in HL7 messages, said Brull. "These sequences begin and end with the message's escape character – usually "\" – and contain an identifying character followed by zero or more characters." The most common use of these escape sequences, he said, is the escape the HL7 characters defined above. 

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