Defining Post-coordinated Clinical Meanings

SNOMED CT enables the use of postcoordinated expressions to represent detailed clinical information (such as observations or procedures) by reference to multiple Concept Identifiers. Expression templates can be used to enable the easy and consistent authoring of postcoordinated expressions and are useful in situations where a specific pattern is needed to support the entry, storage and retrieval of SNOMED CT expressions.  Hence, expression templates are useful for:

• creating batches of postcoordinated expressions
• composing postcoordinated expressions from data entered into a user interface

Batch authoring of postcoordinated expressions

Expression templates may be applied to satisfy a preference for a consistent postcoordinated representation of a particular type of data. For example, there may be a preference to always represent allergies by postcoordinating the disorder with the substance, rather than using one of the precoordinated 'allergic to x' concepts . In this situation,  given a predefined set of substances, an expression template can support the batch authoring of postcoordinated expressions and thus represent the concerned allergic disorders consistently, as illustrated below.

Composing Postcoordinated Expressions from Data Entered into a User Interface

Expression Templates are also useful for creating postcoordinated expressions from data entered using a simple user interface. For example, a specialized radiology coding system may have the option to capture the radiology procedure and the body site to which the procedure was applied. In this situation, an expression template can be defined to specify the syntactically valid expression for a specific radiology procedure with a given direct procedure site (see diagram below).