The accompanying subclass of an observation within a report ingested from Health Report Manager,
preserved exactly as the source message carried it.
Present only when the source field was populated, and copied without normalisation, trimming or
validation. Treat it as opaque.
The same string is normally also the observation's code. Where it is present it becomes
Observation.code.coding.code under CodeSystem/hrm-subclass. It is preserved here because which
source field a given code was built from is not recoverable from code alone.
It is not split, unlike the report-level subclass. The subclass on DiagnosticReport.code is
split on the first ^; this one never is. Values from the two are not guaranteed to be spelled
alike even under the same code system.
Nexus EMR writes this today at
http://services.well.com/fhir/observation/hrm-accompanying-subclass (FHIR-372): it is live in
stored Observation.extension entries and in code, and is under migration to the canonical
declared here. Write the canonical; expect both until the migration completes.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.
Source of the definition for the extension code - a logical name or a URL.
Comments
The definition may point directly to a computable or human-readable definition of the extensibility codes, or it may be a logical URI as declared in some other specification. The definition SHALL be a URI for the Structure Definition defining the extension.
Accompanying subclass, verbatim from the source message
Definition
The accompanying subclass string as the source message carried it, unsplit and unnormalised. Opaque: do not parse it, and do not assume two sending facilities use the same string alike.