Addressed in FHIR-34537 with additional Must Support references in all QI-Core Observation profiles. Specific to QI Core Observation profile built off of FHIR (I.e., the generic one not associated with a specific US Core profile), in addition to the existing constraints, add the following Must Support elements: subject - Must Support for QICorePatient, QICoreDevice, QICoreLocation effective [x] - Must Support for effectiveDateTime, effectivePeriod, effectiveTiming, effectiveInstant performer - add Must Support for this element and for references QICorePractitioner, QICoreOrganization, QICorePatient, QICoreRelatedPerson value [x] - add MustSupport for valueQuantity, valueCodeableConcept with Preferred binding to US Core Observation Value Codes (SNOMEDCT) , valueString, valueBoolean, valueInteger, valueRange, valueRatio, valueTime, valueDateTime, valuePeriod bodySite - change to Preferred binding for SNOMEDCTBodyStructures method - change to Preferred binding for ObservationMethods component.code - change to Preferred binding to LOINC codes value [x] - add MustSupport for valueQuantity, valueCodeableConcept with Preferred binding to US Core Observation Value Codes (SNOMEDCT) , valueString, valueBoolean, valueInteger, valueRange, valueRatio, valueTime, valueDateTime, valuePeriod