http://hl7.org/fhir/StructureDefinition/observation-sequelTo|5.2.0

This observation follows the target observation (e.g. timed tests such as Glucose Tolerance Test).
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/Reference
Extension.value[x].targetProfilehttp://hl7.org/fhir/StructureDefinition/Observation