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The Observation Request Identity subject represents the request or order for a test, procedure or observation. An observation is a result value of observation requests, types of observation values and the constraints on these values. This allows context sharing among systems at the order level.
Observation subjects have the following attributes:
| Subject Label | “Observation” |
| Subject type | Identity |
| Synchronization | Constant |
| Security | None |
| Subject Dependencies | Dependent on patient subject |
| Mapping Agent Coupon Value | -4 |
An application can manage multiple observation types. It may not be capable of establishing the Observation Request context for all observation types. Such is the case for a Central Data Repository (CDR) that accumulates results from multiple sources. A CDR will be unable to set the observation request subject if the required data to set the context (i.e. order number) is not supplied by one or more source system. In such a case an Observation-Link-enabled CDR application should set the observation request context to empty.
A typical observation request(i.e. an order) is associated with one system making the request. However, more than one system may process or hold the request results. An example would be a chest X-ray order where the results consist of textual impressions (i.e. report) and supporting images. The report results may be on one system whereas a PACS system has the associated images. In such a situation, both systems may use the same order number to identify two different results. A site-defined suffix can be used when defining all the context items of an Observation request subject. An Observation-Link- enabled application should be configurable to use the appropriate suffix (or suffixes) to get or set observation context data. The CCOW standard recommends using the system identifier as defined for the HL7 Message Header Segment component 3 (MSH-3) as the value for the suffix.
Observation subjects have the following standard context data items. An Observation-Linked application should set the value for at least one of the items listed in the following table:
| Observation Request Subject Identifier Item Name | Meaning | Data Type | Semantic Constraints on Values | Case Sensitivity |
|---|---|---|---|---|
| Observation.Id.Placer_Order_Number.Suffix | Placer Order Number per OBR-2 | EI | None | No |
| Observation.Id.Filler_Order_Number.Suffix | Filler Order Number per OBR-3 | EI | None | No |
An application can optionally set values for the corroborating items listed in the following table:
| Observation Request Subject Corroborating Item Name | Meaning | Data Type | Semantic Constraints on Values | Case Sensitivity |
|---|---|---|---|---|
| Observation.Co.System_Id.Suffix | Application Identifier per MSH-3 | HD | None | No |
| Observation.Co.Service_Id.Suffix | Universal Service Identifier per OBR-4 | ST | None | No |
| Observation.Co.Date_Time.Suffix | Observation Date / Time per OBR-7 | TS | None | No |
| Observation.Co.Service_Desc.Suffix | Service Description(component of filler order #)per OBR-3.2 | EI | None | No |
Examples of Observation Subject Items are listed in the following table:
| Example Item Names | Example Item Values |
|---|---|
| Observation.Id.Filler_Order_Number.HIS1 | 0111234519990723134223 |
| Observation.Co.System_Id.HIS1 | HIS1 |
| Observation.Co.Service_Id.ISEKG | EKG |
| Observation.Co.Date_Time.ISEKG | 2009723134223 |