description: References a resource or provides a code or text that specifies a substance that is added to a laboratory specimen (part of the container device or added to the specimen indenpendently). package_name: rs/hl7.fhir.uv.extensions derivation: constraint name: SpecimenAdditive type: Extension elements: extension: {index: 0} url: pattern: {type: uri, value: 'http://hl7.org/fhir/StructureDefinition/specimen-additive'} type: uri index: 1 value: choices: [valueCodeableReference] index: 3 valueCodeableReference: {type: CodeableReference, choiceOf: value, index: 4} package_version: 5.1.0 extensions: {} class: extension kind: complex-type url: http://hl7.org/fhir/StructureDefinition/specimen-additive base: http://hl7.org/fhir/StructureDefinition/Extension version: 5.1.0 required: [value, valueCodeableReference]