Context has been defined as the circumstances that form the setting for an event, statement, or idea, and in terms of which it can be fully understood.
Contexts that modify the meaning of a diagnosis or procedure may include family history, past history, suspected diagnoses, planned procedures and procedures not done. It is important to understand the context of each statement in a health record, to determine whether or not it is appropriate to for a CDS rule to be applied.
Context can be expressed in a health record in a number of ways. Firstly, a precoordinated expression can be used in which the context is captured in the meaning of the concept. For example, 160303001 |Family history: Diabetes mellitus|. Alternatively, a postcoordinated expression can be used. This is where the meaning is expressed by combining codes in a structured way using SNOMED CT Compositional Grammar . For example:
A third way to express context is to use a context-specific section or field, such as a "Family history section", which captures the context in the meaning of the section or field name. Lastly, it is also possible to use two separate fields - one which captures the finding |Diabetes mellitus|, and the other which captures the context |Family history of disorder|.
|Technique for Representing Context||Example|
Precoordinated as a single SNOMED CT concept identifier explicitly representing family history of diabetes mellitus.
Postcoordinated as a SNOMED CT expression that includes a concept representing a family history of disorder and specifies the diabetes mellitus as the disorder.
A context specific family history section in the record structure
A separate field in the record structure to indicate the context of the disorder recorded
Considering context that is captured in either the terminology or the information structure is important when executing CDS rules.
In the following example, a CDS rule is triggered inappropriately (i.e. false positive):
In the following example, a CDS rule is not triggered when required (i.e. false negative):
When neither the SNOMED CT concept nor the surrounding health record explicitly states the context, a default context applies.
For clinical findings, it is assumed that the finding is known to be present (as opposed to known to be absent), we assume that the finding is about the patient ( as opposed to someone else), and we assume that the finding occurred at either the present time or a time specified in the record structure ( as opposed to a general time in the past).
The following diagram illustrates how additional context can be captured during the data entry process. The diagnosis (disorder) of 372064008 |Female breast cancer|is selected using the pick-list in the top left corner of the screen and then the context values are selected using the other radio button and pick-list. These context values for relation to subject and finding context must be considered when the conditions in this CDS rule are evaluated.
Figure 3.1.1-1: Capturing context during data entry
It is important to always consider context when defining (and executing) the conditions in a CDS rule. If the default context applies to the condition, then it does not need to be explicitly stated in the CDS rule. However, care should be taken when testing the CDS condition against health records, to ensure that the recorded values share the same context as is required by the CDS rule. If a non-default context is required in a CDS rule, then the rule must explicitly state the context that is required. This context must also be appropriately checked when testing the CDS condition against health records.
The following diagram illustrates a CDS rule, which explicitly states the context of a 372064008 |Female breast cancer|diagnosis that must be matched in order for the action to be triggered. In this example, the CDS condition requires that for patients over the age of 30 258707000 |years|, a diagnosis of 372064008 |Female breast cancer|must be present, in a female family member of the subject, with genetic ties.
Figure 3.1.1-2: CDS rule with the context explicitly stated
The contextual selections in the data entry screen above would satisfy the conditions in this rule because the user has specified that the diagnosis of female breast cancer occurred in the mother of the subject. This can be seen in the postcoordinated expression below, which corresponds to the user's selections in the data entry screen:
Note that a selection of 65412001 |Stepmother|would not trigger the rule as this concept is not a descendant of 444148008 |Person in family of subject|. (Stepmother has no genetic relationship to the patient.)