Clinical Document Architecture
The HL7 Clinical Document Architecture (CDA) is an XML-based markup standard intended to specify the encoding, structure and semantics of clinical documents for exchange. CDA is an ANSI-certified standard from Health Level Seven (HL7.org). Release 1.0 was published in November, 2000 and Release 2.0 was published with the HL7 2005 Normative Edition.
CDA specifies the syntax and supplies a framework for specifying the full semantics of a clinical document. It defines a clinical document as having the following six characteristics:
- Potential for authentication
- Human readability
A CDA can contain any type of clinical content. Typical CDA documents would be a Discharge Summary, Imaging Report, Admission & Physical, Pathology Report and so on. CDA uses XML, although it allows for a non-XML body (pdf, Word, jpg and so on) for simple implementations.
It was developed using the HL7 Development Framework (HDF) and it is based on the HL7 Reference Information Model (RIM) and the HL7 Version 3 Data Types.
The CDA specifies that the content of the document consists of a mandatory textual part (which ensures human interpretation of the document contents) and optional structured parts (for software processing). The structured part relies on coding systems (such as from SNOMED and LOINC) to represent concepts.
The CDA standard doesn't specify how the documents should be transported. CDA documents can be transported using HL7 version 2 messages, HL7 version 3 messages, IHE protocols such as XDS, as well as by other mechanisms including: DICOM, MIME attachments to email, http or ftp.
Country specific notes 
In the U.S. the CDA standard is probably best known as the basis for the Continuity of Care Document (CCD) specification, based on the data model as specified by ASTMs Continuity of Care Record. The U.S. Healthcare Information Technology Standards Panel has selected the CCD as one of its standards.
See also 
- Health Informatics Service Architecture (HISA)
- Continuity of Care Record
- Continuity of Care Document
- Gello Expression Language