Editing Health Level 7 (section)

===HL7 Version 2===
{{Technical|date=April 2024|section}}
The HL7 version 2 standard (also known as Pipehat) has the aim to support hospital workflows. It was originally created in 1989.<ref>{{cite web|title=HL7 FAQs|url=http://www.hl7.org/about/FAQs/index.cfm?ref=nav|publisher=[[HL7]]}}</ref>

HL7 version 2 defines a series of electronic messages to support administrative, logistical, financial as well as clinical processes. Since 1987 the standard has been updated regularly, resulting in more than ten iterations. The v2.x standards are [[Backward compatibility|backward compatible]], meaning a message based on version 2.3 will be understood by an application that supports version 2.6.

HL7 v2.x messages use a non-[[XML]] encoding syntax based on segments ([[Line (text file)|line]]s) and one-character [[delimiter]]s.<ref>{{cite web|title=Understanding HL7 Messages|url=http://www.interfaceware.com/understanding_hl7_messages.html|publisher=iNTERFACEWARE}}</ref> Segments have composites ([[Field (computer science)|field]]s) separated by the composite delimiter. A composite can have sub-composites (components) separated by the sub-composite delimiter, and sub-composites can have sub-sub-composites (subcomponents) separated by the sub-sub-composite delimiter. The default delimiters are [[carriage return]] for the segment separator, vertical bar or pipe (<code>|</code>) for the field separator, caret (<code>^</code>) for the component separator, ampersand (<code>&</code>) for the subcomponent separator, and number sign (#) for the default truncation separator. The tilde (<code>~</code>) is the default repetition separator. Each segment starts with a 3-character string that identifies the segment type. Each segment of the message contains one specific category of information. Every message has <code>MSH</code> as its first segment, which includes a field that identifies the message type. The message type determines the expected segment types in the message.<ref>{{cite web|title=HL7 Messages and Descriptions|url=http://healthstandards.com/blog/2007/09/24/hl7-separator-characters/|publisher=Health Standards}}</ref> The segment types used in a particular message type are specified by the segment grammar notation used in the HL7 standards.

The following is an example of an admission message.  <code>MSH</code> is the header segment, <code>PID</code> the Patient Identity, <code>PV1</code> is the Patient Visit information, etc. The 5th field in the <code>PID</code> segment is the patient's name, in the order, family name, given name, second name (or their initials), suffix, etc. Depending on the HL7 V2.x standard version, more fields are available in the segment for additional patient information.

{{pre|
<nowiki>MSH|^~\&|MegaReg|XYZHospC|SuperOE|XYZImgCtr|20060529090131-0500||ADT^A01^ADT_A01|01052901|P|2.5
EVN||200605290901||||
PID|||56782445^^^UAReg^PI||KLEINSAMPLE^BARRY^Q^JR||19620910|M||2028-9^^HL70005^RA99113^^XYZ|260 GOODWIN CREST DRIVE^^BIRMINGHAM^AL^35209^^M~NICKELL’S PICKLES^10000 W 100TH AVE^BIRMINGHAM^AL^35200^^O|||||||0105I30001^^^99DEF^AN
PV1||I|W^389^1^UABH^^^^3||||12345^MORGAN^REX^J^^^MD^0010^UAMC^L||67890^GRAINGER^LUCY^X^^^MD^0010^UAMC^L|MED|||||A0||13579^POTTER^SHERMAN^T^^^MD^0010^UAMC^L|||||||||||||||||||||||||||200605290900
OBX|1|NM|^Body Height||1.80|m^Meter^ISO+|||||F
OBX|2|NM|^Body Weight||79|kg^Kilogram^ISO+|||||F
AL1|1||^ASPIRIN
DG1|1||786.50^CHEST PAIN, UNSPECIFIED^I9|||A</nowiki>
}}

HL7 v2.x has allowed for the [[interoperability]] between the plethora of digital health systems, from Patient Administration Systems, to Electronic Health Records, and specialised Laboratory and Radiology Information Systems. Currently, the HL7 v2.x messaging standard is supported by every major health informatics vendor in the United States.<ref>{{cite web|title=Standards Organizations|url=http://aspe.hhs.gov/sp/nhii/standards.html|publisher=Assistant Secretary for Planning and Evaluation (ASPE), [[Health and Human Services]] (HHS)}}</ref>