Use of HL7 templates in CP

Patient Care | Patient Care Normative Ballot Content

Use of Templates in Care Provision

HL7 Templates

An HL7 template is a constraint on models based on the HL7 Reference Information Model (RIM). It expresses the data content needed in a specific clinical or administrative context.

In healthcare there are prescribed patterns by which, for example, multiple observations may be combined to describe selected, gross observations. Some observations may be simple, such as the single lab result (e.g. potassium in blood is 4.4 mEq/L) or the blood pressure concept, which involves a set of expected observations (i.e., systolic, diastolic, patient position, method, etc.). Other more elaborate diagnostic procedures may involve hundreds of related pieces of information, including anatomy, orientation, sequences of measurements, etc.

In HL7, more or less generic models exist; the Patient Care model, especially the Care Statements = Clinical Statement Pattern (CSP) is one of it. Templates provide a method of describing rules for combining and constraining HL7 v3 XML instances like a Patient Care message. Templates can be used for three purposes:

• To have a guideline to create (a fragment of) a Patient Care message instance
• To validate an instance whether it conforms to the specified template rules
• To have a guidance while processing a Patient Care message instance.

Based on user need and preference, the template ideally is a structure that can be used as a building block and, once defined, can be re-used whenever appropriate.

Kinds of Patient Care templates

The Patient Care standard describes conformance requirements in terms of two general levels:

• Message root level templates: they define / refine the overall structure of a message starting from the Care Provision class, which templates are contained in the message and whether they are optional or required.
• Substructure level templates (patient, provider etc.)
• Clinical Statement level templates: impose the Clinical Statement Pattern of a Patient Care message; they define the constraints on the classes, class attributes, data types and class relationships.

Template Identifiers in instances

Template identifiers (templateId) are assigned at the Message root level and Clinical Statement level. When valued in an instance, the template identifier signals the imposition of a set of template-defined constraints. The value of this attribute, e.g.

<templateId root="2.16.840.1.113883.10.1.2.3" />

provides a unique identifier for the template in question.

If a template is a specialization of another template, its first constraint indicates the more general template. The general template is not always required. In all cases where a more specific template conforms to a more general template, asserting the more specific template also implies conformance to the more general template.

Open and Closed Templates

In open templates, all of the features of the Patient Care based specification are allowed except as constrained by the templates. By contrast, a closed template specifies everything that is allowed and nothing further may be included.

Open templates allow HL7 implementers to develop additional content not constrained within the template. HL7 encourages implementers to bring their use cases forward as candidate requirements to be formalized in a subsequent version of the standard to maximize the use of shared semantics.

In general, Patient Care defines open templates only.

Originator Responsibilities: General Case

An originator can apply a templateId if there is a desire to assert conformance with a particular template.

In the most general forms of CDA exchange, an originator need not apply a templateId for every template that an object in an instance document conforms to. The implementation guide (IG) shall assert whenever templateIds are required for conformance.