CDA Documents may reference information contained in other documents. While CDA Release
2.0 supports references in content via the <linkHtml> element, this is insufficient
for many EMR systems as the link is assumed to be accessible via a URL, which is often
not the case. In order to link an external reference, one needs the document identifier,
and access to the clinical system wherein the document resides. For a variety of reasons,
it is desirable to refer to the document by its identity, rather than by linking through
a URL.
The identity of a document does not change, but the URLs used to access it may vary
depending upon location, implementation, or other factors.
Referencing clinical documents by identity does not impose any implementation specific
constraints on the mechanism used to resolve these references, allowing the content
to be implementation neutral. For example, in the context of an XDS Affinity domain
the clinical system used to access documents would be an XDS Registry and one or more
XDS Repositories where documents are stored. In other contexts, access might be through
a Clinical Data Repository (CDR), or Document Content Management System (DCMS). Each
of these may have different mechanisms to resolve a document
identifier to the document resource.
The identity of a document is known before the document is published (e.g., in an
XDS Repository, Clinical Data Repository, or Document Content Management System),
but its URL is often not known. Using the document identity allows references to existing
documents to be created before those documents have been published to a URL. This
is important to document creators, as it does not impose workflow restrictions on
how links are created during the authoring process.
Fortunately, CDA Release 2.0 also provides a mechanism to refer to external documents
in an entry, as shown below.
Classification
CDA Entry Level Template
Open/Closed
Open (other than defined elements are allowed)
Used by / Uses
Used by 0 transactions and 2 templates, Uses 0 templates
The <templateId> element identifies this <act> as a reference act, allowing for validation
of the content. As a side effect, readers of the CDA can quickly locate and identify
reference acts.
The reference is an act of itself, and must be uniquely identified. If there is no
explicit identifier for this act in the source EMR system, a GUID may be used for
the root attribute, and the extension may be omitted.
In order to connect this external reference to the narrative text which it refers,
the value of the <reference> element in the <text> element is a URI to an element
in the CDA narrative of this document.
Reference pointing to the narrative, typically #{label}-{generated-id}, e.g. #xxx-1
hl7:reference
R
External references are listed as either supporting documentation (typeCode='SPRT')
or simply reference material (typeCode='REFR') for the reader. If this distinction
is not supported by the source EMR system, the value of typeCode should be REFR. For
CDA, the reference is indicated by a <reference> element containing an <externalDocument>
element which documents (classCode='DOC') the event (moodCode='EVN'). For HL7 Version
3 Messages, the reference is represented with the element <sourceOf> and the external
document is represented
with a <act> element, however semantics, and attributes remain otherwise without change.
A link to the original document may be provided here. This shall be a URL where the
referenced document can be located. For CDA, the link should also be present in the
narrative inside the CDA Narrative in a <linkHTML> element.
Template External Reference
nce)