HL7

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HL7 refers to a standards development organization, as well as some of the specific standards it has created over the years, especially HL7 v2.

HL7, the organization

Health Level Seven International (HL7) is a non-profit, standards development organization which develops and promulgates standards for interoperability in clinical practice. The organization has more than 1,600 members from around the world, including corporate members representing healthcare providers, government stakeholders, payers, and various commercial interests. [1]

HL7 is accreditated by ANSI (the American National Standards Institute), an umbrella organization of sorts for Standards Development Organizations in the US.

The term "Level Seven" refers to the seventh level in the seven-layer OSI model Open Systems Interconnection (OSI) communications model - the application level. The application level interfaces directly to and performs common application services for the application processes. HL7's protocols largely exist at the application layer, providing the infrastructure for various applications to interconnect seamlessly.

History

Founded in 1987, the Health Level Seven (HL7) protocol and corporation behind it are a standard means for exchanging clinical data. Currently in its third version, this standard describes a framework for the exchange of messages related to patient registrations, lab results, pharmaceutical orders, inventory, billing, et cetera between and within care-delivery systems and organizations. “Health Level Seven” is an allusion to the Open Systems Interconnection (OSI) model’s “Level Seven”, the conceptual network layer at which data is exchanged between applications and the lower networking layers and infrastructure. As such, the protocol accepts data from disparate applications, packages it into an appropriately formatted message type with various header and identifying information, and facilitates its transmission across TCP/IP connections between machines hosting these applications.

History of version 2

Currently the most common iteration of the HL7 standard is version 2.x. Messages in this version rely on “triggers” to define the exchange of data. Specific message types exist to signal Admissions, Discharges, and Transfers (ADTs), lab results (ORU), medication administration (RAS) events, et cetera. Upon, e.g., admission of a patient to a hospital, the registration system generates and populates an “ADT” message, of type “A01”. This message is populated with demographic information about the patient recently admitted, to include name and address, next-of-kin information, allergies, and related/relevant diagnoses. Each of these bundles of information is relayed inside an ordered set of reusable “segment” of the message; e.g., Patient IDentifiers are placed inside a segmented component of the ADT message called a “PID segment”. Discrete pieces of information are separated by “delimiters”, which themselves are meaningful; e.g., “…|LastName^FirstName|…|DateOfBirth|Sex|…” might represent a portion of the PID segment, and is delimited using the ‘|’ character to set apart conceptual entities (e.g., name and date-of-birth), and the ‘^’ characer to set apart components of those entities (e.g., first and last name). Some of these components and fields are allowed to repeat, such that a single lab result message may contain the results of several ordered labs for a given patient. The various segments which comprise the HL7 message are then prefixed with a MeSsage Header (MSH) segment, describing the message itself, (optionally) an EVeNt (EVN) segment, describing the event which “triggered” that message, and then transmitted through a TCP/IP connection to a receiving application’s interface server where the message is parsed into component values and consumed.


Example

An example of an HL7 message follows. Note how quickly you can guess the meanings of the fields and even segments within this message signaling the admission of a patient:

MSH|^~\&|||||200501100455||ADT^A01|ADT66561|P|2.3||||||| 
PID|||10006579||DUCK^DONALD D||19241010|M|||111^QUACK ST^^FOWL^CA^99999^^R||8885551212|||||40007716|123121234
PV1||I|PREOP^101^1||||37^DISNEY^WALT|||||||||||I||||||||||||||||||||||||||200501100452 
DG1|1|||OSTEOARTHROS NOS-L/LEG

Version 3 new additions

  1. Top-down message development emphasizing reuse across multiple contexts
  2. Representation of complex temporal and non-temporal relationships
  3. Formalisms for vocabulary support
  4. Support for large scale integration
  5. Solving the identifiers problem
  6. Solving re-use and interoperability across multiple domain contexts
  7. Expanded scope to include community medicine, epidemiology, veterinary medicine, clinical #genomics, security, etc.


The HL7 Clinical Document Architecture (CDA) is an ANSI standard with release 2 being published early in 2005 [1]. Like other HL7 standards it is based on the reference information model (RIM) and is designed to capture information as a document and then be stored in EHR systems.

Features

A feature of the CDA is its ability to be viewed in a browser using a single style sheet, ensuring everyone can read the record. Structured information can also be recorded and be used in different systems. The information is recognizable by different systems through use of shared terminology, such as SNOMED and LOINC.

Inter nationality

The CDA standard holds great potential for sharing information and is being trialed in many countries including the Netherlands, Spain, Germany, Japan and Mexico to name a few.


References

  1. Dolin RH, Alschuler L, Boyer S, Beebe C, Behlen FM, Biron PV, Shabo A. HL7 Clinical Document Architecture, Release 2. J Am Med Inform Assoc. 2005 Oct 12;
  2. http://www.hl7.org/documentcenter/public_temp_4BF5D005-1C23-BA17-0CE1A58E38D45506/strategic/roadmap/HL7_2012_Strategic_Initiatives%20FINAL.pdf
  3. Dolin RH, Alschuler L, Boyer S, Beebe C, Behlen FM, Biron PV, Shabo Shvo A. HL7 Clinical Document Architecture, Release 2. J Am Med Inform Assoc. 2006 Jan-Feb;13(1):30-9. Epub 2005 Oct 12.
  1. http://www.hl7.org/about/index.cfm

Submitted by Leah Lewis