What is HL7® CDA™?
An XML markup standard that specifies the structure and semantics of “clinical documents” for the purpose of exchange. Originally presented at the HL7® Plenary meeting in September of 1998. CDA™ Release 1.0 was approved as an ANSI standard on November of 2000. CDA™ Release 2.0 was approved as an ANSI standard on May of 2005.
The CDA™ is part of the HL7 version 3 family of standards. This family, which includes both CDA™ and the evolving version 3 message standards, all derive their semantic content from the shared HL7 Reference Information Model (RIM) and are implemented in Extensible Markup Language (XML). The process for generating an XML-based implementation from the RIM is part of the version 3 development methodology. The exact style of HL7’s XML representation was a carefully considered balance of technical, practical, and functional considerations.
The Features of the HL7 CDA™ standard are listed below:
- Persistence: A clinical document continues to exist in an unaltered state, for a time period defined by local and regulatory requirements.
- Stewardship: A clinical document is maintained by a person or organization entrusted with its care.
- Potential for authentication: A clinical document is an assemblage of iformation that is intended to be legally authenticated.
- Wholeness: Authentication of a clinical document applies to the whole and does not apply to portions of the document without the full context of the document.
- Human readability : A clinical document is human readable, guarantees that a receiver of a CDA™ document can readily display the clinical content of the note on a standard Web browser.
- Context: A clinical document establishes the default context for its contents.
The goals of HL7® CDA™:
- Give priority to delivery of patient care.
- Cost effective implementation in a wide spectrum of healthcare computer systems.
- Exchange of human readable documents between users regardless of their technical sophistication.
- Promote longevity of all information encoded.
- Enable a wide range of post-exchange processing applications.
- Compatibility with a variety of document creation applications.
- Prepare to design reasonably quickly.
- Information requirements control capability for policy-makers.
A CDA™ document is a defined and complete information object that can include text, images, sounds, and other multimedia content. The document can be sent inside an HL7 message and can exist independently outside a transferring message. There is a critical interdependence between clinical documents and document management systems. If CDA™ documents are viewed outside the context of a document management system, it cannot be known with certainty whether or not the viewed document is current. Clinical documents can be revised, and they can be appended to existing documents. In practice, it is impossible to guarantee an explicit forward pointer from an outdated version to the newer version. Document management systems and HL7 messages that carry CDA™ documents convey critical contextual information that minimizes the risk of viewing superseded information.
HL7® CDA™ documents must be human readable which means that the receiver of a document can display clinical content in a standard Web browser. The clinical content of the document is rendered in the browser using dedicated XSLT stylesheet. There is no requirement for originator of the document to transmit a stylesheet during exchange, and the document itself must be displayable using any standard XSLT stylesheet designed for CDA™ documents presentation. The rule of human readability applies to the authenticated content.
HL7® CDA™ defines three levels of implementation of the standard.
Level One is sufficiently detailed to represent largely narrative clinical notes. The specification defines the document header in detail, while the document body is largely structural. Level One is intended to minimize the technical barriers to adoption of the standard while providing a gentle introduction to the RIM. It intentionally lacks some of the complex semantics that will be used in HL7 version 3 messaging (such as the ability to fully encode orders and observations). It is hoped that the provision of deeper levels of the architecture will provide a migration pathway for implementers to iteratively add greater markup to clinical documents.
Level Two is envisioned as a set of templates or constraints that can be layered on top of the CDA™ Level One specification. A template may, for instance, specify that a document of type “history-and-physical” will contain a mandatory “subjective” section; a mandatory “physical-examination” section containing a mandatory “vital-signs” section and an optional “cardiovascular-examination” section; and a mandatory “assessment” section followed by a “plan” section. This type of template development will require considerable domain knowledge and participation from professional societies so that created templates are widely embraced and supported. Health Level 7 is now in the process of establishing necessary liaison relationships with professional societies.
Level Three of the CDA™ will add additional RIM-derived markup to the CDA™ Level One specification, enabling clinical content to be formally expressed to the extent that is it modeled in the RIM or to the extent that it can be expressed in an HL7 version 3 message. This could, for instance, allow an order message to be extracted from a clinical document, allow for a detailed representation of symptoms and findings, and allow for billing codes to be automatically extracted.
The clinical content of CDA™ documents will remain invariable across all levels of the architecture. Each level both enables and enhances the standardized expression of richer shared semantics. Thus, a single report can be marked up as a Level One, Level Two, or Level Three document, and its clinical content will not vary.