The element,   DiagnosticReport.basedOn,  is not defined in the US Core DiagnosticReport Profile for Laboratory Results Reporting. As we document in the  General Guidance page Many of the profiles in this guide  reference  other FHIR resources that are also US Core Profiles. These references are defined in the formal profile definitions. For example,  US Core CareTeam Profile  references US Core Patient. For any other references to base FHIR resources 1  or  not formally defined in a US Core Profiles, the referenced resource  SHOULD  be a US Core Profile if a US Core Profile exists for the resource type.