Altova Technology Primer: HL7 Technology Overview

Health Level 7 (HL7)

HL7 is a major consideration for healthcare IT professionals, particularly as the incentives (and eventually disincentives) legislated in the Health Information Technology for Economic and Clinical Health (HITECH) Act of 2009 kick in. In effect mandating the adoption of electronic health records (EHRs), the HITECH Act has guaranteed the relevance of HL7 for many years to come – interoperability among healthcare IT systems, the EHR in particular, is the foundation of the technical infrastructure that the HITECH Act was designed to promote.

HL7 isn’t a language per se but rather a set of standards that dictate the format in which electronic information is exchanged between otherwise disassociated healthcare systems.

HL7 also refers to Health Level Seven International, the organization certified by the American National Standards Institute (ANSI) to develop the protocols that define HL7 message exchange. The organization takes its name from Level 7, the highest layer of the International Standards Organization’s (ISO) Open System Interconnection (OSI) model.

An HL7 message is composed of a series of segments, each of which identifies the type of information the message contains (e.g., diagnosis, insurance, observation result). In turn, each segment includes one or more composites (or fields) that carry the actual information being conveyed (e.g., name, test value, dosage). In short, an HL7 message is defined by its structure as well as by the information that it contains.

HL7 data model

The ACKnowledgment Protocol is a key element of HL7’s utility in a healthcare setting. Once an HL7 message is received, the recipient system returns an acknowledgment with message status (received and processed, error detected, or rejected). If the application that initiated the communication does not receive an acknowledgement, it will continue to send the message – only when an “ACK” message is received will it stop transmitting and take corrective action if necessary.

HL7 is not just a single set of standards. In addition to messaging standards there are HL7 standards for clinical decision support (GELLO), transportable healthcare-specific rules (the Arden Syntax), visual integration (CCOW), attachments (Standard Healthcare Attachments), exchange of clinical documents (Clinical Document Architecture or CDA®), EHR and personal health record (PHRs) systems and medication documentation (Structured Product Labeling).

One recent and notable advancement in HL7 messaging is the break with v2.x EDI-based standards. The latest incarnation of this messaging standard is HL7 v3.x, an XML-based standard that forms the base of more recent developments including the GELLO language, CDA, and Structured Product Labeling.

Of significance to developers is the fact that HL7 v3.x is (intentionally) NOT backwards compatible with HL7 v2.x – HL7 hoped to develop a messaging standard that would meet the needs of the healthcare community today and into the future without concern for existing standards. Data mapping between HL7 v2.x-compliant applications and those compliant with the new XML-based v3.x standards will be required.

The workgroups tasked with developing HL7 v3.x base all protocols on the Reference Information Model (RIM), a UML class model outlining information requirements and interactions across all clinical areas. The RIM is a comprehensive resource and includes class diagrams, state-machine diagrams, interaction overviews, use case diagrams, etc. ANSI certified the RIM as a standard in 2003 and ISO followed in 2006.

HL7’s role in the future of healthcare IT has been secured as a result of legislation designed to create a technical infrastructure for the healthcare industry and the ongoing quest for interoperability occurring across all industries. Given these drivers, compliance with both EDI and XML-based HL7 standards will continue be an integral component of any healthcare application.

Altova provides comprehensive support for IT professionals working with HL7 standards – please click for more information about Altova’s HL7 tools.