HL7 CDA

by Lyniate

#HL7 #CDA

CDA is an XML-based, electronic standard used for clinical document exchange that was developed by Health Level Seven. CDA conforms to the HL7 V3 Implementation Technology Specification (ITS), is based on the HL7 Reference Information Model (RIM), and uses HL7 V3 data types. It was known earlier as the Patient Record Architecture (PRA).

CDA is a flexible standard and is unique in that it can be read by the human eye or processed by a machine. This is due to its use of XML language, which also allows the standard to be broken into two different parts. A mandatory free-form portion enables human interpretation of the document, while an optional structured part enables electronic processing (like with an EMR system). Text, images, and even multimedia can be included in the document.

A CDA document could be, for example, any of the following: discharge summary, referral, clinical summary, history/physical examination, diagnostic report, prescription, or public health report. In short, any document that might have a signature is a viable document for CDA.

Implementation of CDA

CDA does not specify a transport mechanism and can be utilized within a messaging environment or outside of it. Transport methods can include HL7 V2, HL7 V3, DICOM, MIME-encoded attachments, HTTP, or FTP. CDA is flexible enough to be compatible in a wide range of environments, and can be stored as a document in a computer system (permanently or temporarily) or can be transmitted as the content of a message.

In current practice, the Summary of Care Consolidated CDA is the document type primarily used in the United States due to the mandate required by Meaningful Use. Other examples of international implementations of CDA include: PICNIC (Ireland, Denmark, Crete), SCHIPHOX (Germany), MERIT-9 (Japan), Staffordshire EHR (United Kingdom), and Regional Health Information System – Satakunta Macropilot (Finland).

CDA Structure

CDA is an XML document that consists of a header and body. It is presented in this format:

Header – includes patient information, author, creation date, document type, provider, etc.
Body – includes clinical details, diagnosis, medications, follow-up, etc. Presented as free text in one or multiple sections, and may optionally also include coded entries.

CDA has three levels of document definition as defined by the HL7 organization, with Level One providing the least structure and Levels Two and Three providing greater structure:

Level One – the root hierarchy, and the most unconstrained version of the document. Level One supports full CDA semantics, and has limited coding ability for the contents. An example of a level one constraint on document type would be a “Discharge Summary” with only textual instructions.
Level Two – additional constraints on the document via templates at the “Section” (free text) level. An example of a level two constraint would be a “Discharge Summary” with a section coded as Medications.
Level Three – additional constraints on the document at the “Entry” (encoded content) level, and optional additional constraints at the “Section” level. An example of a level three constraint would be a “Discharge Summary” with a section coded as Medications with coded RxNORM entries for each medication.

Additional information can be found on the HL7 Standards resource site and in Lyniate’s HL7 Resource Center.

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