In context of https://jira.hl7.org/browse/FHIR-28375 we propose that the Reference list be limited to US Core Practitioner Profile and all other base standard choices be optional.

A human being is the primary party of interest as the performer.  The data source should not be required to just be able to document an Organization.  Therefore, Organization should remain optional with the other choices allowed by the base standard.  We also note that CLIA required data on medical director and performing lab is communicated be at the Observation level (see HL7 v2 and HL7 C-CDA as well), further reducing the need to require Organization as a Must Support on DiagnosticReport.performer.

As the FHIR US Core profile is used for accessing and exchanging data based on what the source system has, this should not require the data source system to add functionality to capture a patient as part of the diagnostic report for lab results.  Additionally, C-CDA does not impose this requirement either.

Links to pages:

http://hl7.org/fhir/us/core/STU3.1/StructureDefinition-us-core-diagnosticreport-lab.html

https://build.fhir.org/ig/HL7/US-Core-R4/StructureDefinition-us-core-diagnosticreport-lab.html