Health Level-7 or HL7 refers to a set of international standards for transfer of clinical and administrative data between software applications used by various healthcare providers. These standards focus on the application layer, which is "layer 7" in the OSI model. The HL7 standards are produced by the Health Level Seven International, an international standards organization, and are adopted by other standards issuing bodies such as American National Standards Institute and International Organization for Standardization.

Hospitals and other healthcare provider organizations typically have many different computer systems used for everything from billing records to patient tracking. All of these systems should communicate with each other (or "interface") when they receive new information, or when they wish to retrieve information, but not all do so.

HL7 International specifies a number of flexible standards, guidelines, and methodologies by which various healthcare systems can communicate with each other. Such guidelines or data standards are a set of rules that allow information to be shared and processed in a uniform and consistent manner. These data standards are meant to allow healthcare organizations to easily share clinical information. Theoretically, this ability to exchange information should help to minimize the tendency for medical care to be geographically isolated and highly variable.

HL7 International considers the following standards to be its primary standards - those standards that are most commonly used and implemented:

Version 2.x Messaging Standard – an interoperability specification for health and medical transactions

Version 3 Messaging Standard – an interoperability specification for health and medical transactions

Clinical Document Architecture (CDA) – an exchange model for clinical documents, based on HL7 Version 3

Continuity of Care Document (CCD) - a US specification for the exchange of medical summaries, based on CDA.

Structured Product Labeling (SPL) – the published information that accompanies a medicine, based on HL7 Version 3

Clinical Context Object Workgroup (CCOW) – an interoperability specification for the visual integration of user applications

Other HL7 standards/methodologies include:

Fast Healthcare Interoperability Resources (FHIR) - a draft standard for the exchange of resources

Arden Syntax – a grammar for representing medical conditions and recommendations as a Medical Logic Module (MLM)

Claims Attachments – a Standard Healthcare Attachment to augment another healthcare transaction

Functional Specification of Electronic Health Record (EHR) / Personal Health Record (PHR) systems - a standardized description of health and medical functions sought for or available in such software applications

GELLO – a standard expression language used for clinical decision support

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