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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