http://hl7.org/fhir/StructureDefinition/observation-nature-of-abnormal-test|5.2.0

This field contains the nature of the abnormal test. This is represented in v2 as OBX-10 Nature of abnormal test (ID) 00578.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/CodeableConcept
Extension.value[x].binding.valueSethttp://terminology.hl7.org/ValueSet/v2-0080