Maintenance and Management

Managing the components used to represent the large number of clinical data entries in EHRs is an important part of the work related to maintaining the integrity and accessibility of health information. Like SNOMED CT components, reference sets are supported by a robust versioning mechanism that allows historically consistent views of SNOMED CT components and derivatives. This allows reference sets to be used to specify changes in use of concepts and descriptions in different parts of an EHR.

For more detailed use cases, please refer to the following examples:

Constrain Value Sets

Most health records are designed and developed using one or more information models, which describe the information that is collected, stored, communicated and displayed. Some information models are designed for a specific proprietary system, while others are based on a common health information standard. Irrespective of the purpose, design and representation of the information models, the use of clinical terminology is an important part of making the models complete, meaningful and useful. Hence, a consistent approach to the interface between structural elements and terminological representations of information is required to support reliable interpretation of the meaning. Subsets of SNOMED CT components can function as value sets for any health-related information model to enable well-defined, unambiguous models of meaning.

As shown in the diagram below simple reference sets can be used to represent the subsets of SNOMED CT components to be populated as value sets within the relevant information models.

Managing Value Sets

EHR systems will typically utilize a range of different value sets to be used in different places of the system. Representing these value sets using the same terminology will support the comparison of data captured in different contexts. Additionally, using SNOMED CT to represent items value sets instead of locally defined terms enables effective management and overview of information, and helps to mitigate challenges related to redundancy and ambiguity.

Simple reference sets can be used to represent extensionally defined subsets of SNOMED CT components, whereas the query specification reference set are useful for representing the intensional definition of SNOMED CT subsets. In the query specification reference set, the expression constraints can be used to represent the query used for defining the set. This means that the query specification reference set can be used to manage the intensional definition of SNOMED CT subsets that function as value sets, which is illustrated below.

When a component that is a member of a reference set is inactivated, the person maintaining the reference set needs to decide whether a change is required. This depends on the intended use of the reference set being maintained. In the case of a reference set that is being used to constrain data entry, inactive concepts need to be removed from the reference set or replaced by an appropriate active concept. In other reference sets it may be permissible, or even required, to retain an inactive concept in a reference set (for example if a reference set is used in the criteria for a report which may be applied to historical data).

The following figure and subsequent description introduce the overall process for identifying inactive components and using released reference sets to determine reasons for inactivation and potential replacements.

1. One approach to identify the components that have been inactivated since the last release, is to compare snapshot of previous release with current delta release.

2. The reasons for inactivation can be looked up in the 900000000000480006 | Attribute value type reference set| for the particular component type, for example the 900000000000489007 | Concept inactivation indicator attribute value reference set| . The reason is represented by the value of the valueId attribute. For further information, see .

3. The possible replacements for the components that have been inactivated can be determined in the appropriate 900000000000522004 | Historical association reference set|

In the International Edition of SNOMED CT three reference sets of the type 900000000000480006 | Attribute value type reference set| are used to indicate the reason why components have been inactivated. These are:

• 900000000000489007 | Concept inactivation indicator attribute value reference set (foundation metadata concept)|

• 900000000000490003 | Description inactivation indicator attribute value reference set (foundation metadata concept)|

• 900000000000547002 | Relationship inactivation indicator attribute value reference set (foundation metadata concept)|

For example, if the inactivated component is marked as 900000000000484002 | Ambiguous| , this will typically mean that there will be more than one component replacing the inactivated component. The possible replacements will be available in the 900000000000523009 | POSSIBLY EQUIVALENT TO association reference set (foundation metadata concept)| .

Another example is concepts that are inactivated because they were 900000000000482003 | Duplicate| . This is used if two concepts represent the same meaning, because then one of those concepts must be inactivated. The equivalent concept will be represented in the 900000000000527005 | SAME AS association reference set (foundation metadata concept)| . Please refer to to see which reference sets relate to the various reasons for inactivation.

When a new version of SNOMED CT is released this may include changes to the content of the terminology. Components may have been added, inactivated or changed as described in . As part of the terminology maintenance process, it may be appropriate to evaluate both the and to determine appropriate alternatives.

The International Edition of SNOMED CT distributes a set of reference sets that record the reason that each inactive component was inactivated. These are referred to as "historical association" reference sets. There is one historical association reference set for each type of historical association as shown in the table below.

Table: Association reference set types in the International Release of SNOMED CT

The following table holds example entries for the 900000000000526001 | Replaced by| reference set. With this reference set is possible to automatically identify that the inactive concept 696005 | Chronobiologic disorder| should be replaced with the concept 387605007 | Abnormal chronobiologic state| . This type of reference set is particularly useful for ensuring consistent use of SNOMED CT over time. The reference set mechanism here provides an easy and standardized way of managing changes to coding or documentation practice over time.

Table: Sample content from 900000000000526001 | REPLACED BY association reference set |