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.

Representing Context in a Health Record

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, . 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:

281666001 |Family history of disorder|:
   246090004 |Associated finding| = 73211009 |Diabetes mellitus|

 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 , and the other which captures the context . 

Techniques for recording context in an EHR

281666001 |Family history of disorder|:
   246090004 |Associated finding| = 73211009 |Diabetes mellitus|

False Positives and False Negatives 

Considering context that is captured in either the terminology or the information structure is important when executing CDS rules.

• Logic based purely on the presence or absence of codes, without considering the context implied by the information structure, may lead to CDS alerts being triggered unnecessarily (i.e. false positives).
• Conversely, logic based purely on the presence or absence of codes, without considering context implied by the information structure, may lead to CDS alerts not being triggered when required (ie. false negatives).

False Positive Example

In the following example, a CDS rule is triggered inappropriately (i.e. false positive):

• A CDS rule is designed to display clinical practice guidelines for stage 1 chronic kidney disease when the code  is found in the EHR. A retrospective analysis of a false positive trigger reveals that the code was recorded in the past history section of the health record. As this record indicates that the  was part of the patient's , the display of stage 1 chronic kidney disease guidelines was inappropriate.

False Negative Example

In the following example, a CDS rule is not triggered when required (i.e. false negative):

• A CDS rule is designed to display patient-focused, preventative educational material when the code  is found in the EHR. This rule is implemented in an EHR system, which uses a family history section to record the family history of disorders. Even though the SNOMED CT concept  is recorded in the patient's family history, the CDS rule is not triggered as required.

Default Context

When neither the SNOMED CT concept nor the surrounding health record explicitly states the context, a default context applies.

Default context values alongside their corresponding attributes

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). 

Data Entry with Context

The following diagram illustrates how additional context can be captured during the data entry process. The diagnosis (disorder) of 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.

Capturing context during data entry

Defining Context in Rules

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 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 , a diagnosis of must be present, in a female family member of the subject, with genetic ties.

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:

372064008 |Female breast cancer|:
   408729009 |Finding context| = 410515003 |Known present|,
   408732007 |Subject relationship context| = 444301002 |Mother of subject|

Note that a selection of would not trigger the rule as this concept is not a descendant of . (Stepmother has no genetic relationship to the patient.)