description: This extension links this observation with the certified reference material used for the calibration.\nThe certified reference material is identified by using an Identifier.\nThis extension should be used when the unit is UCUM [IU]. package_name: hl7.fhir.eu.laboratory derivation: constraint name: ObservationCertifiedRefMaterialIdentifer type: Extension elements: extension: {index: 0} url: pattern: {type: Uri, value: 'http://hl7.eu/fhir/laboratory/StructureDefinition/observation-certifiedRefMaterialIdentifer'} index: 1 value: choices: [valueIdentifier] index: 3 valueIdentifier: {type: Identifier, choiceOf: value, index: 4} package_version: 2.0.0 extensions: {} class: extension kind: complex-type url: http://hl7.eu/fhir/laboratory/StructureDefinition/observation-certifiedRefMaterialIdentifer base: http://hl7.org/fhir/StructureDefinition/Extension version: 2.0.0