Virtually Healthcare HL7 FHIR R4 Implementation Guide
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Virtually Healthcare HL7 FHIR R4 Implementation Guide, published by Virtually Healthcare. This guide is not an authorized publication; it is the continuous build for version 0.1.0-current built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/Virtually-Healthcare/HL7-FHIR-Implementation-Guide/ and changes regularly. See the Directory of published versions

Resource Profile: AllergyIntolerance - Detailed Descriptions

Draft as of 2024-12-02

Definitions for the AllergyIntolerance resource profile.

Guidance on how to interpret the contents of this table can be found here

0. AllergyIntolerance
2. AllergyIntolerance.identifier
NoteThis is a business identifier, not a resource identifier (see discussion)
Control1..?
TypeIdentifier(Common Resource Identifiers)
Must Supporttrue
4. AllergyIntolerance.code
6. AllergyIntolerance.code.coding
SlicingThis element introduces a set of slices on AllergyIntolerance.code.coding. The slices areUnordered and Closed, and can be differentiated using the following discriminators:
  • value @ system
  • 8. AllergyIntolerance.code.coding:SNOMED
    Slice NameSNOMED
    Control0..*
    BindingThe codes SHALL be taken from UK Core Allergy Code
    (required to https://fhir.hl7.org.uk/ValueSet/UKCore-AllergyCode)
    Must Supporttrue
    10. AllergyIntolerance.code.coding:SNOMED.system
    Control1..?
    Pattern Valuehttp://snomed.info/sct
    12. AllergyIntolerance.patient
    14. AllergyIntolerance.patient.identifier
    NoteThis is a business identifier, not a resource identifier (see discussion)
    TypeIdentifier(NHS, HCSN and CHI Numbers)

    Guidance on how to interpret the contents of this table can be found here

    0. AllergyIntolerance
    Definition

    Risk of harmful or undesirable, physiological response which is unique to an individual and associated with exposure to a substance.

    ShortAllergy or Intolerance (generally: Risk of adverse reaction to a substance)
    Comments

    Substances include, but are not limited to: a therapeutic substance administered correctly at an appropriate dosage for the individual; food; material derived from plants or animals; or venom from insect stings.

    Control0..*
    Is Modifierfalse
    Summaryfalse
    Alternate NamesAllergy, Intolerance, Adverse Reaction
    Invariantsait-1: AllergyIntolerance.clinicalStatus SHALL be present if verificationStatus is not entered-in-error. (verificationStatus.coding.where(system = 'http://terminology.hl7.org/CodeSystem/allergyintolerance-verification' and code = 'entered-in-error').exists() or clinicalStatus.exists())
    ait-2: AllergyIntolerance.clinicalStatus SHALL NOT be present if verification Status is entered-in-error (verificationStatus.coding.where(system = 'http://terminology.hl7.org/CodeSystem/allergyintolerance-verification' and code = 'entered-in-error').empty() or clinicalStatus.empty())
    dom-2: If the resource is contained in another resource, it SHALL NOT contain nested Resources (contained.contained.empty())
    dom-3: If the resource is contained in another resource, it SHALL be referred to from elsewhere in the resource or SHALL refer to the containing resource (contained.where((('#'+id in (%resource.descendants().reference | %resource.descendants().as(canonical) | %resource.descendants().as(uri) | %resource.descendants().as(url))) or descendants().where(reference = '#').exists() or descendants().where(as(canonical) = '#').exists() or descendants().where(as(canonical) = '#').exists()).not()).trace('unmatched', id).empty())
    dom-4: If a resource is contained in another resource, it SHALL NOT have a meta.versionId or a meta.lastUpdated (contained.meta.versionId.empty() and contained.meta.lastUpdated.empty())
    dom-5: If a resource is contained in another resource, it SHALL NOT have a security label (contained.meta.security.empty())
    dom-6: A resource should have narrative for robust management (text.`div`.exists())
    ait-1: AllergyIntolerance.clinicalStatus SHALL be present if verificationStatus is not entered-in-error. (verificationStatus.coding.where(system = 'http://terminology.hl7.org/CodeSystem/allergyintolerance-verification' and code = 'entered-in-error').exists() or clinicalStatus.exists())
    ait-2: AllergyIntolerance.clinicalStatus SHALL NOT be present if verification Status is entered-in-error (verificationStatus.coding.where(system = 'http://terminology.hl7.org/CodeSystem/allergyintolerance-verification' and code = 'entered-in-error').empty() or clinicalStatus.empty())
    2. AllergyIntolerance.implicitRules
    Definition

    A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.

    ShortA set of rules under which this content was created
    Comments

    Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of it's narrative along with other profiles, value sets, etc.

    Control0..1
    Typeuri
    Is Modifiertrue because This element is labeled as a modifier because the implicit rules may provide additional knowledge about the resource that modifies it's meaning or interpretation
    Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
    Summarytrue
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    4. AllergyIntolerance.modifierExtension
    Definition

    May be used to represent additional information that is not part of the basic definition of the resource and that modifies the understanding of the element that contains it and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer is allowed to define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.

    Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

    ShortExtensions that cannot be ignored
    Comments

    There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

    Control0..*
    TypeExtension
    Is Modifiertrue because Modifier extensions are expected to modify the meaning or interpretation of the resource that contains them
    Summaryfalse
    Requirements

    Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

    Alternate Namesextensions, user content
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
    6. AllergyIntolerance.identifier
    Definition

    An identifier - identifies some entity uniquely and unambiguously. Typically this is used for business identifiers.


    Business identifiers assigned to this AllergyIntolerance by the performer or other systems which remain constant as the resource is updated and propagates from server to server.

    ShortAn identifier intended for computationExternal ids for this item
    Comments

    This is a business identifier, not a resource identifier (see discussion). It is best practice for the identifier to only appear on a single resource instance, however business practices may occasionally dictate that multiple resource instances with the same identifier can exist - possibly even with different resource types. For example, multiple Patient and a Person resource instance might share the same social insurance number.

    NoteThis is a business identifier, not a resource identifier (see discussion)
    Control10..*
    This element is affected by the following invariants: ele-1
    TypeIdentifier(Common Resource Identifiers)
    Is Modifierfalse
    Must Supporttrue
    Requirements

    Allows identification of the AllergyIntolerance as it is known by various participating systems and in a way that remains consistent across servers.

    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    8. AllergyIntolerance.clinicalStatus
    Definition

    The clinical status of the allergy or intolerance.

    Shortactive | inactive | resolved
    Comments

    Refer to discussion if clincalStatus is missing data. The data type is CodeableConcept because clinicalStatus has some clinical judgment involved, such that there might need to be more specificity than the required FHIR value set allows. For example, a SNOMED coding might allow for additional specificity.

    Control0..1
    This element is affected by the following invariants: ait-1, ait-2
    BindingThe codes SHALL be taken from AllergyIntoleranceClinicalStatusCodeshttp://hl7.org/fhir/ValueSet/allergyintolerance-clinical|4.0.1
    (required to http://hl7.org/fhir/ValueSet/allergyintolerance-clinical|4.0.1)

    The clinical status of the allergy or intolerance.

    TypeCodeableConcept
    Is Modifiertrue because This element is labeled as a modifier because the status contains the codes inactive and resolved that mark the AllergyIntolerance as no longer active.
    Must Supporttrue
    Summarytrue
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    10. AllergyIntolerance.verificationStatus
    Definition

    Assertion about certainty associated with the propensity, or potential risk, of a reaction to the identified substance (including pharmaceutical product).

    Shortunconfirmed | confirmed | refuted | entered-in-error
    Comments

    The data type is CodeableConcept because verificationStatus has some clinical judgment involved, such that there might need to be more specificity than the required FHIR value set allows. For example, a SNOMED coding might allow for additional specificity.

    Control0..1
    This element is affected by the following invariants: ait-1, ait-2
    BindingThe codes SHALL be taken from AllergyIntoleranceVerificationStatusCodeshttp://hl7.org/fhir/ValueSet/allergyintolerance-verification|4.0.1
    (required to http://hl7.org/fhir/ValueSet/allergyintolerance-verification|4.0.1)

    Assertion about certainty associated with a propensity, or potential risk, of a reaction to the identified substance.

    TypeCodeableConcept
    Is Modifiertrue because This element is labeled as a modifier because the status contains the codes refuted and entered-in-error that mark the AllergyIntolerance as not currently valid.
    Must Supporttrue
    Summarytrue
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    12. AllergyIntolerance.code
    Definition

    Code for an allergy or intolerance statement (either a positive or a negated/excluded statement). This may be a code for a substance or pharmaceutical product that is considered to be responsible for the adverse reaction risk (e.g., "Latex"), an allergy or intolerance condition (e.g., "Latex allergy"), or a negated/excluded code for a specific substance or class (e.g., "No latex allergy") or a general or categorical negated statement (e.g., "No known allergy", "No known drug allergies"). Note: the substance for a specific reaction may be different from the substance identified as the cause of the risk, but it must be consistent with it. For instance, it may be a more specific substance (e.g. a brand medication) or a composite product that includes the identified substance. It must be clinically safe to only process the 'code' and ignore the 'reaction.substance'. If a receiving system is unable to confirm that AllergyIntolerance.reaction.substance falls within the semantic scope of AllergyIntolerance.code, then the receiving system should ignore AllergyIntolerance.reaction.substance.

    ShortCode that identifies the allergy or intolerance
    Comments

    It is strongly recommended that this element be populated using a terminology, where possible. For example, some terminologies used include RxNorm, SNOMED CT, DM+D, NDFRT, ICD-9, IDC-10, UNII, and ATC. Plain text should only be used if there is no appropriate terminology available. Additional details can be specified in the text.

    When a substance or product code is specified for the 'code' element, the "default" semantic context is that this is a positive statement of an allergy or intolerance (depending on the value of the 'type' element, if present) condition to the specified substance/product. In the corresponding SNOMED CT allergy model, the specified substance/product is the target (destination) of the "Causative agent" relationship.

    The 'substanceExposureRisk' extension is available as a structured and more flexible alternative to the 'code' element for making positive or negative allergy or intolerance statements. This extension provides the capability to make "no known allergy" (or "no risk of adverse reaction") statements regarding any coded substance/product (including cases when a pre-coordinated "no allergy to x" concept for that substance/product does not exist). If the 'substanceExposureRisk' extension is present, the AllergyIntolerance.code element SHALL be omitted.

    Control10..1
    BindingFor example codes, see AllergyIntoleranceSubstance/Product,ConditionAndNegationCodeshttp://hl7.org/fhir/ValueSet/allergyintolerance-code
    (example to http://hl7.org/fhir/ValueSet/allergyintolerance-code)

    Type of the substance/product, allergy or intolerance condition, or negation/exclusion codes for reporting no known allergies.

    TypeCodeableConcept
    Is Modifierfalse
    Must Supporttrue
    Summarytrue
    Alternate NamesCode
    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    14. AllergyIntolerance.code.coding
    Definition

    A reference to a code defined by a terminology system.

    ShortCode defined by a terminology system
    Comments

    Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.

    Control0..*
    TypeCoding
    Is Modifierfalse
    Summarytrue
    Requirements

    Allows for alternative encodings within a code system, and translations to other code systems.

    Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
    SlicingThis element introduces a set of slices on AllergyIntolerance.code.coding. The slices areUnordered and Closed, and can be differentiated using the following discriminators:
    • value @ system
    • 16. AllergyIntolerance.code.coding:SNOMED
      Slice NameSNOMED
      Definition

      A reference to a code defined by a terminology system.

      ShortCode defined by a terminology system
      Comments

      Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.

      Control0..*
      BindingThe codes SHALL be taken from For codes, see UK Core Allergy Code
      (required to https://fhir.hl7.org.uk/ValueSet/UKCore-AllergyCode)
      TypeCoding
      Is Modifierfalse
      Must Supporttrue
      Summarytrue
      Requirements

      Allows for alternative encodings within a code system, and translations to other code systems.

      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      18. AllergyIntolerance.code.coding:SNOMED.system
      Definition

      The identification of the code system that defines the meaning of the symbol in the code.

      ShortIdentity of the terminology system
      Comments

      The URI may be an OID (urn:oid:...) or a UUID (urn:uuid:...). OIDs and UUIDs SHALL be references to the HL7 OID registry. Otherwise, the URI should come from HL7's list of FHIR defined special URIs or it should reference to some definition that establishes the system clearly and unambiguously.

      Control10..1
      Typeuri
      Is Modifierfalse
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      Summarytrue
      Requirements

      Need to be unambiguous about the source of the definition of the symbol.

      Pattern Valuehttp://snomed.info/sct
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      20. AllergyIntolerance.patient
      Definition

      The patient who has the allergy or intolerance.

      ShortWho the sensitivity is for
      Control1..1
      TypeReference(IPA-Patient, Patient)
      Is Modifierfalse
      Must Supporttrue
      Summarytrue
      Alternate NamesPatient
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      22. AllergyIntolerance.patient.identifier
      Definition

      An identifier - identifies some entity uniquely and unambiguously. Typically this is used for business identifiers.


      An identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

      ShortAn identifier intended for computationLogical reference, when literal reference is not known
      Comments

      When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

      When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

      Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

      Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

      NoteThis is a business identifier, not a resource identifier (see discussion)
      Control0..1
      This element is affected by the following invariants: ele-1
      TypeIdentifier(NHS, HCSN and CHI Numbers)
      Is Modifierfalse
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))

      Guidance on how to interpret the contents of this table can be found here

      0. AllergyIntolerance
      Definition

      Risk of harmful or undesirable, physiological response which is unique to an individual and associated with exposure to a substance.

      ShortAllergy or Intolerance (generally: Risk of adverse reaction to a substance)
      Comments

      Substances include, but are not limited to: a therapeutic substance administered correctly at an appropriate dosage for the individual; food; material derived from plants or animals; or venom from insect stings.

      Control0..*
      Is Modifierfalse
      Summaryfalse
      Alternate NamesAllergy, Intolerance, Adverse Reaction
      Invariantsait-1: AllergyIntolerance.clinicalStatus SHALL be present if verificationStatus is not entered-in-error. (verificationStatus.coding.where(system = 'http://terminology.hl7.org/CodeSystem/allergyintolerance-verification' and code = 'entered-in-error').exists() or clinicalStatus.exists())
      ait-2: AllergyIntolerance.clinicalStatus SHALL NOT be present if verification Status is entered-in-error (verificationStatus.coding.where(system = 'http://terminology.hl7.org/CodeSystem/allergyintolerance-verification' and code = 'entered-in-error').empty() or clinicalStatus.empty())
      dom-2: If the resource is contained in another resource, it SHALL NOT contain nested Resources (contained.contained.empty())
      dom-3: If the resource is contained in another resource, it SHALL be referred to from elsewhere in the resource or SHALL refer to the containing resource (contained.where((('#'+id in (%resource.descendants().reference | %resource.descendants().as(canonical) | %resource.descendants().as(uri) | %resource.descendants().as(url))) or descendants().where(reference = '#').exists() or descendants().where(as(canonical) = '#').exists() or descendants().where(as(canonical) = '#').exists()).not()).trace('unmatched', id).empty())
      dom-4: If a resource is contained in another resource, it SHALL NOT have a meta.versionId or a meta.lastUpdated (contained.meta.versionId.empty() and contained.meta.lastUpdated.empty())
      dom-5: If a resource is contained in another resource, it SHALL NOT have a security label (contained.meta.security.empty())
      dom-6: A resource should have narrative for robust management (text.`div`.exists())
      2. AllergyIntolerance.id
      Definition

      The logical id of the resource, as used in the URL for the resource. Once assigned, this value never changes.

      ShortLogical id of this artifact
      Comments

      The only time that a resource does not have an id is when it is being submitted to the server using a create operation.

      Control0..1
      Typeid
      Is Modifierfalse
      Summarytrue
      4. AllergyIntolerance.meta
      Definition

      The metadata about the resource. This is content that is maintained by the infrastructure. Changes to the content might not always be associated with version changes to the resource.

      ShortMetadata about the resource
      Control0..1
      TypeMeta
      Is Modifierfalse
      Summarytrue
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      6. AllergyIntolerance.implicitRules
      Definition

      A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.

      ShortA set of rules under which this content was created
      Comments

      Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of it's narrative along with other profiles, value sets, etc.

      Control0..1
      Typeuri
      Is Modifiertrue because This element is labeled as a modifier because the implicit rules may provide additional knowledge about the resource that modifies it's meaning or interpretation
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      Summarytrue
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      8. AllergyIntolerance.language
      Definition

      The base language in which the resource is written.

      ShortLanguage of the resource content
      Comments

      Language is provided to support indexing and accessibility (typically, services such as text to speech use the language tag). The html language tag in the narrative applies to the narrative. The language tag on the resource may be used to specify the language of other presentations generated from the data in the resource. Not all the content has to be in the base language. The Resource.language should not be assumed to apply to the narrative automatically. If a language is specified, it should it also be specified on the div element in the html (see rules in HTML5 for information about the relationship between xml:lang and the html lang attribute).

      Control0..1
      BindingThe codes SHOULD be taken from CommonLanguages
      (preferred to http://hl7.org/fhir/ValueSet/languages)

      A human language.

      Additional BindingsPurpose
      AllLanguagesMax Binding
      Typecode
      Is Modifierfalse
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      Summaryfalse
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      10. AllergyIntolerance.text
      Definition

      A human-readable narrative that contains a summary of the resource and can be used to represent the content of the resource to a human. The narrative need not encode all the structured data, but is required to contain sufficient detail to make it "clinically safe" for a human to just read the narrative. Resource definitions may define what content should be represented in the narrative to ensure clinical safety.

      ShortText summary of the resource, for human interpretation
      Comments

      Contained resources do not have narrative. Resources that are not contained SHOULD have a narrative. In some cases, a resource may only have text with little or no additional discrete data (as long as all minOccurs=1 elements are satisfied). This may be necessary for data from legacy systems where information is captured as a "text blob" or where text is additionally entered raw or narrated and encoded information is added later.

      Control0..1
      TypeNarrative
      Is Modifierfalse
      Summaryfalse
      Alternate Namesnarrative, html, xhtml, display
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      12. AllergyIntolerance.contained
      Definition

      These resources do not have an independent existence apart from the resource that contains them - they cannot be identified independently, and nor can they have their own independent transaction scope.

      ShortContained, inline Resources
      Comments

      This should never be done when the content can be identified properly, as once identification is lost, it is extremely difficult (and context dependent) to restore it again. Contained resources may have profiles and tags In their meta elements, but SHALL NOT have security labels.

      Control0..*
      TypeResource
      Is Modifierfalse
      Summaryfalse
      Alternate Namesinline resources, anonymous resources, contained resources
      14. AllergyIntolerance.extension
      Definition

      May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

      ShortAdditional content defined by implementations
      Comments

      There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

      Control0..*
      TypeExtension
      Is Modifierfalse
      Summaryfalse
      Alternate Namesextensions, user content
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
      16. AllergyIntolerance.modifierExtension
      Definition

      May be used to represent additional information that is not part of the basic definition of the resource and that modifies the understanding of the element that contains it and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer is allowed to define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.

      Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

      ShortExtensions that cannot be ignored
      Comments

      There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

      Control0..*
      TypeExtension
      Is Modifiertrue because Modifier extensions are expected to modify the meaning or interpretation of the resource that contains them
      Summaryfalse
      Requirements

      Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

      Alternate Namesextensions, user content
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
      18. AllergyIntolerance.identifier
      Definition

      An identifier - identifies some entity uniquely and unambiguously. Typically this is used for business identifiers.

      ShortAn identifier intended for computation
      Comments

      This is a business identifier, not a resource identifier (see discussion). It is best practice for the identifier to only appear on a single resource instance, however business practices may occasionally dictate that multiple resource instances with the same identifier can exist - possibly even with different resource types. For example, multiple Patient and a Person resource instance might share the same social insurance number.

      NoteThis is a business identifier, not a resource identifier (see discussion)
      Control1..*
      This element is affected by the following invariants: ele-1
      TypeIdentifier(Common Resource Identifiers)
      Is Modifierfalse
      Must Supporttrue
      Requirements

      Allows identification of the AllergyIntolerance as it is known by various participating systems and in a way that remains consistent across servers.

      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      20. AllergyIntolerance.clinicalStatus
      Definition

      The clinical status of the allergy or intolerance.

      Shortactive | inactive | resolved
      Comments

      Refer to discussion if clincalStatus is missing data. The data type is CodeableConcept because clinicalStatus has some clinical judgment involved, such that there might need to be more specificity than the required FHIR value set allows. For example, a SNOMED coding might allow for additional specificity.

      Control0..1
      This element is affected by the following invariants: ait-1, ait-2
      BindingThe codes SHALL be taken from AllergyIntoleranceClinicalStatusCodes
      (required to http://hl7.org/fhir/ValueSet/allergyintolerance-clinical|4.0.1)

      The clinical status of the allergy or intolerance.

      TypeCodeableConcept
      Is Modifiertrue because This element is labeled as a modifier because the status contains the codes inactive and resolved that mark the AllergyIntolerance as no longer active.
      Must Supporttrue
      Summarytrue
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      22. AllergyIntolerance.verificationStatus
      Definition

      Assertion about certainty associated with the propensity, or potential risk, of a reaction to the identified substance (including pharmaceutical product).

      Shortunconfirmed | confirmed | refuted | entered-in-error
      Comments

      The data type is CodeableConcept because verificationStatus has some clinical judgment involved, such that there might need to be more specificity than the required FHIR value set allows. For example, a SNOMED coding might allow for additional specificity.

      Control0..1
      This element is affected by the following invariants: ait-1, ait-2
      BindingThe codes SHALL be taken from AllergyIntoleranceVerificationStatusCodes
      (required to http://hl7.org/fhir/ValueSet/allergyintolerance-verification|4.0.1)

      Assertion about certainty associated with a propensity, or potential risk, of a reaction to the identified substance.

      TypeCodeableConcept
      Is Modifiertrue because This element is labeled as a modifier because the status contains the codes refuted and entered-in-error that mark the AllergyIntolerance as not currently valid.
      Must Supporttrue
      Summarytrue
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      24. AllergyIntolerance.type
      Definition

      Identification of the underlying physiological mechanism for the reaction risk.

      Shortallergy | intolerance - Underlying mechanism (if known)
      Comments

      Allergic (typically immune-mediated) reactions have been traditionally regarded as an indicator for potential escalation to significant future risk. Contemporary knowledge suggests that some reactions previously thought to be immune-mediated are, in fact, non-immune, but in some cases can still pose a life threatening risk. It is acknowledged that many clinicians might not be in a position to distinguish the mechanism of a particular reaction. Often the term "allergy" is used rather generically and may overlap with the use of "intolerance" - in practice the boundaries between these two concepts might not be well-defined or understood. This data element is included nevertheless, because many legacy systems have captured this attribute. Immunologic testing may provide supporting evidence for the basis of the reaction and the causative substance, but no tests are 100% sensitive or specific for sensitivity to a particular substance. If, as is commonly the case, it is unclear whether the reaction is due to an allergy or an intolerance, then the type element should be omitted from the resource.

      Control0..1
      BindingThe codes SHALL be taken from AllergyIntoleranceType
      (required to http://hl7.org/fhir/ValueSet/allergy-intolerance-type|4.0.1)

      Identification of the underlying physiological mechanism for a Reaction Risk.

      Typecode
      Is Modifierfalse
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      Summarytrue
      Alternate NamesCategory, Class
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      26. AllergyIntolerance.category
      Definition

      Category of the identified substance.

      Shortfood | medication | environment | biologic
      Comments

      This data element has been included because it is currently being captured in some clinical systems. This data can be derived from the substance where coding systems are used, and is effectively redundant in that situation. When searching on category, consider the implications of AllergyIntolerance resources without a category. For example, when searching on category = medication, medication allergies that don't have a category valued will not be returned. Refer to search for more information on how to search category with a :missing modifier to get allergies that don't have a category. Additionally, category should be used with caution because category can be subjective based on the sender.

      Control0..*
      BindingThe codes SHALL be taken from AllergyIntoleranceCategory
      (required to http://hl7.org/fhir/ValueSet/allergy-intolerance-category|4.0.1)

      Category of an identified substance associated with allergies or intolerances.

      Typecode
      Is Modifierfalse
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      Summarytrue
      Alternate NamesCategory, Type, Reaction Type, Class
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      28. AllergyIntolerance.criticality
      Definition

      Estimate of the potential clinical harm, or seriousness, of the reaction to the identified substance.

      Shortlow | high | unable-to-assess
      Comments

      The default criticality value for any propensity to an adverse reaction should be 'Low Risk', indicating at the very least a relative contraindication to deliberate or voluntary exposure to the substance. 'High Risk' is flagged if the clinician has identified a propensity for a more serious or potentially life-threatening reaction, such as anaphylaxis, and implies an absolute contraindication to deliberate or voluntary exposure to the substance. If this element is missing, the criticality is unknown (though it may be known elsewhere). Systems that capture a severity at the condition level are actually representing the concept of criticality whereas the severity documented at the reaction level is representing the true reaction severity. Existing systems that are capturing both condition criticality and reaction severity may use the term "severity" to represent both. Criticality is the worst it could be in the future (i.e. situation-agnostic) whereas severity is situation-dependent.

      Control0..1
      BindingThe codes SHALL be taken from AllergyIntoleranceCriticality
      (required to http://hl7.org/fhir/ValueSet/allergy-intolerance-criticality|4.0.1)

      Estimate of the potential clinical harm, or seriousness, of a reaction to an identified substance.

      Typecode
      Is Modifierfalse
      Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
      Summarytrue
      Alternate NamesSeverity, Seriousness, Contra-indication, Risk
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      30. AllergyIntolerance.code
      Definition

      Code for an allergy or intolerance statement (either a positive or a negated/excluded statement). This may be a code for a substance or pharmaceutical product that is considered to be responsible for the adverse reaction risk (e.g., "Latex"), an allergy or intolerance condition (e.g., "Latex allergy"), or a negated/excluded code for a specific substance or class (e.g., "No latex allergy") or a general or categorical negated statement (e.g., "No known allergy", "No known drug allergies"). Note: the substance for a specific reaction may be different from the substance identified as the cause of the risk, but it must be consistent with it. For instance, it may be a more specific substance (e.g. a brand medication) or a composite product that includes the identified substance. It must be clinically safe to only process the 'code' and ignore the 'reaction.substance'. If a receiving system is unable to confirm that AllergyIntolerance.reaction.substance falls within the semantic scope of AllergyIntolerance.code, then the receiving system should ignore AllergyIntolerance.reaction.substance.

      ShortCode that identifies the allergy or intolerance
      Comments

      It is strongly recommended that this element be populated using a terminology, where possible. For example, some terminologies used include RxNorm, SNOMED CT, DM+D, NDFRT, ICD-9, IDC-10, UNII, and ATC. Plain text should only be used if there is no appropriate terminology available. Additional details can be specified in the text.

      When a substance or product code is specified for the 'code' element, the "default" semantic context is that this is a positive statement of an allergy or intolerance (depending on the value of the 'type' element, if present) condition to the specified substance/product. In the corresponding SNOMED CT allergy model, the specified substance/product is the target (destination) of the "Causative agent" relationship.

      The 'substanceExposureRisk' extension is available as a structured and more flexible alternative to the 'code' element for making positive or negative allergy or intolerance statements. This extension provides the capability to make "no known allergy" (or "no risk of adverse reaction") statements regarding any coded substance/product (including cases when a pre-coordinated "no allergy to x" concept for that substance/product does not exist). If the 'substanceExposureRisk' extension is present, the AllergyIntolerance.code element SHALL be omitted.

      Control1..1
      BindingFor example codes, see AllergyIntoleranceSubstance/Product,ConditionAndNegationCodes
      (example to http://hl7.org/fhir/ValueSet/allergyintolerance-code)

      Type of the substance/product, allergy or intolerance condition, or negation/exclusion codes for reporting no known allergies.

      TypeCodeableConcept
      Is Modifierfalse
      Must Supporttrue
      Summarytrue
      Alternate NamesCode
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      32. AllergyIntolerance.code.id
      Definition

      Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

      ShortUnique id for inter-element referencing
      Control0..1
      Typestring
      Is Modifierfalse
      XML FormatIn the XML format, this property is represented as an attribute.
      Summaryfalse
      34. AllergyIntolerance.code.extension
      Definition

      May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

      ShortAdditional content defined by implementations
      Comments

      There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

      Control0..*
      TypeExtension
      Is Modifierfalse
      Summaryfalse
      Alternate Namesextensions, user content
      Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
      ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
      SlicingThis element introduces a set of slices on AllergyIntolerance.code.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
      • value @ url
      • 36. AllergyIntolerance.code.coding
        Definition

        A reference to a code defined by a terminology system.

        ShortCode defined by a terminology system
        Comments

        Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.

        Control0..*
        TypeCoding
        Is Modifierfalse
        Summarytrue
        Requirements

        Allows for alternative encodings within a code system, and translations to other code systems.

        Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
        SlicingThis element introduces a set of slices on AllergyIntolerance.code.coding. The slices areUnordered and Closed, and can be differentiated using the following discriminators:
        • value @ system
        • 38. AllergyIntolerance.code.coding:SNOMED
          Slice NameSNOMED
          Definition

          A reference to a code defined by a terminology system.

          ShortCode defined by a terminology system
          Comments

          Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.

          Control0..*
          BindingThe codes SHALL be taken from UK Core Allergy Code
          (required to https://fhir.hl7.org.uk/ValueSet/UKCore-AllergyCode)
          TypeCoding
          Is Modifierfalse
          Must Supporttrue
          Summarytrue
          Requirements

          Allows for alternative encodings within a code system, and translations to other code systems.

          Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
          40. AllergyIntolerance.code.coding:SNOMED.id
          Definition

          Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

          ShortUnique id for inter-element referencing
          Control0..1
          Typestring
          Is Modifierfalse
          XML FormatIn the XML format, this property is represented as an attribute.
          Summaryfalse
          42. AllergyIntolerance.code.coding:SNOMED.extension
          Definition

          May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

          ShortAdditional content defined by implementations
          Comments

          There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

          Control0..*
          TypeExtension
          Is Modifierfalse
          Summaryfalse
          Alternate Namesextensions, user content
          Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
          ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
          SlicingThis element introduces a set of slices on AllergyIntolerance.code.coding.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
          • value @ url
          • 44. AllergyIntolerance.code.coding:SNOMED.system
            Definition

            The identification of the code system that defines the meaning of the symbol in the code.

            ShortIdentity of the terminology system
            Comments

            The URI may be an OID (urn:oid:...) or a UUID (urn:uuid:...). OIDs and UUIDs SHALL be references to the HL7 OID registry. Otherwise, the URI should come from HL7's list of FHIR defined special URIs or it should reference to some definition that establishes the system clearly and unambiguously.

            Control1..1
            Typeuri
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            Summarytrue
            Requirements

            Need to be unambiguous about the source of the definition of the symbol.

            Pattern Valuehttp://snomed.info/sct
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            46. AllergyIntolerance.code.coding:SNOMED.version
            Definition

            The version of the code system which was used when choosing this code. Note that a well-maintained code system does not need the version reported, because the meaning of codes is consistent across versions. However this cannot consistently be assured, and when the meaning is not guaranteed to be consistent, the version SHOULD be exchanged.

            ShortVersion of the system - if relevant
            Comments

            Where the terminology does not clearly define what string should be used to identify code system versions, the recommendation is to use the date (expressed in FHIR date format) on which that version was officially published as the version date.

            NoteThis is a business version Id, not a resource version Id (see discussion)
            Control0..1
            Typestring
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            Summarytrue
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            48. AllergyIntolerance.code.coding:SNOMED.code
            Definition

            A symbol in syntax defined by the system. The symbol may be a predefined code or an expression in a syntax defined by the coding system (e.g. post-coordination).

            ShortSymbol in syntax defined by the system
            Control0..1
            Typecode
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            Summarytrue
            Requirements

            Need to refer to a particular code in the system.

            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            50. AllergyIntolerance.code.coding:SNOMED.display
            Definition

            A representation of the meaning of the code in the system, following the rules of the system.

            ShortRepresentation defined by the system
            Control0..1
            Typestring
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            Summarytrue
            Requirements

            Need to be able to carry a human-readable meaning of the code for readers that do not know the system.

            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            52. AllergyIntolerance.code.coding:SNOMED.userSelected
            Definition

            Indicates that this coding was chosen by a user directly - e.g. off a pick list of available items (codes or displays).

            ShortIf this coding was chosen directly by the user
            Comments

            Amongst a set of alternatives, a directly chosen code is the most appropriate starting point for new translations. There is some ambiguity about what exactly 'directly chosen' implies, and trading partner agreement may be needed to clarify the use of this element and its consequences more completely.

            Control0..1
            Typeboolean
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            Summarytrue
            Requirements

            This has been identified as a clinical safety criterium - that this exact system/code pair was chosen explicitly, rather than inferred by the system based on some rules or language processing.

            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            54. AllergyIntolerance.code.text
            Definition

            A human language representation of the concept as seen/selected/uttered by the user who entered the data and/or which represents the intended meaning of the user.

            ShortPlain text representation of the concept
            Comments

            Very often the text is the same as a displayName of one of the codings.

            Control0..1
            Typestring
            Is Modifierfalse
            Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
            Summarytrue
            Requirements

            The codes from the terminologies do not always capture the correct meaning with all the nuances of the human using them, or sometimes there is no appropriate code at all. In these cases, the text is used to capture the full meaning of the source.

            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            56. AllergyIntolerance.patient
            Definition

            The patient who has the allergy or intolerance.

            ShortWho the sensitivity is for
            Control1..1
            TypeReference(IPA-Patient)
            Is Modifierfalse
            Must Supporttrue
            Summarytrue
            Alternate NamesPatient
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            58. AllergyIntolerance.patient.id
            Definition

            Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

            ShortUnique id for inter-element referencing
            Control0..1
            Typestring
            Is Modifierfalse
            XML FormatIn the XML format, this property is represented as an attribute.
            Summaryfalse
            60. AllergyIntolerance.patient.extension
            Definition

            May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

            ShortAdditional content defined by implementations
            Comments

            There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

            Control0..*
            TypeExtension
            Is Modifierfalse
            Summaryfalse
            Alternate Namesextensions, user content
            Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
            ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
            SlicingThis element introduces a set of slices on AllergyIntolerance.patient.extension. The slices areUnordered and Open, and can be differentiated using the following discriminators:
            • value @ url
            • 62. AllergyIntolerance.patient.reference
              Definition

              A reference to a location at which the other resource is found. The reference may be a relative reference, in which case it is relative to the service base URL, or an absolute URL that resolves to the location where the resource is found. The reference may be version specific or not. If the reference is not to a FHIR RESTful server, then it should be assumed to be version specific. Internal fragment references (start with '#') refer to contained resources.

              ShortLiteral reference, Relative, internal or absolute URL
              Comments

              Using absolute URLs provides a stable scalable approach suitable for a cloud/web context, while using relative/logical references provides a flexible approach suitable for use when trading across closed eco-system boundaries. Absolute URLs do not need to point to a FHIR RESTful server, though this is the preferred approach. If the URL conforms to the structure "/[type]/[id]" then it should be assumed that the reference is to a FHIR RESTful server.

              Control0..1
              This element is affected by the following invariants: ref-1
              Typestring
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summarytrue
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              64. AllergyIntolerance.patient.type
              Definition

              The expected type of the target of the reference. If both Reference.type and Reference.reference are populated and Reference.reference is a FHIR URL, both SHALL be consistent.

              The type is the Canonical URL of Resource Definition that is the type this reference refers to. References are URLs that are relative to http://hl7.org/fhir/StructureDefinition/ e.g. "Patient" is a reference to http://hl7.org/fhir/StructureDefinition/Patient. Absolute URLs are only allowed for logical models (and can only be used in references in logical models, not resources).

              ShortType the reference refers to (e.g. "Patient")
              Comments

              This element is used to indicate the type of the target of the reference. This may be used which ever of the other elements are populated (or not). In some cases, the type of the target may be determined by inspection of the reference (e.g. a RESTful URL) or by resolving the target of the reference; if both the type and a reference is provided, the reference SHALL resolve to a resource of the same type as that specified.

              Control0..1
              BindingUnless not suitable, these codes SHALL be taken from ResourceType
              (extensible to http://hl7.org/fhir/ValueSet/resource-types)

              Aa resource (or, for logical models, the URI of the logical model).

              Typeuri
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summarytrue
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              66. AllergyIntolerance.patient.identifier
              Definition

              An identifier - identifies some entity uniquely and unambiguously. Typically this is used for business identifiers.

              ShortAn identifier intended for computation
              Comments

              When an identifier is provided in place of a reference, any system processing the reference will only be able to resolve the identifier to a reference if it understands the business context in which the identifier is used. Sometimes this is global (e.g. a national identifier) but often it is not. For this reason, none of the useful mechanisms described for working with references (e.g. chaining, includes) are possible, nor should servers be expected to be able resolve the reference. Servers may accept an identifier based reference untouched, resolve it, and/or reject it - see CapabilityStatement.rest.resource.referencePolicy.

              When both an identifier and a literal reference are provided, the literal reference is preferred. Applications processing the resource are allowed - but not required - to check that the identifier matches the literal reference

              Applications converting a logical reference to a literal reference may choose to leave the logical reference present, or remove it.

              Reference is intended to point to a structure that can potentially be expressed as a FHIR resource, though there is no need for it to exist as an actual FHIR resource instance - except in as much as an application wishes to actual find the target of the reference. The content referred to be the identifier must meet the logical constraints implied by any limitations on what resource types are permitted for the reference. For example, it would not be legitimate to send the identifier for a drug prescription if the type were Reference(Observation|DiagnosticReport). One of the use-cases for Reference.identifier is the situation where no FHIR representation exists (where the type is Reference (Any).

              NoteThis is a business identifier, not a resource identifier (see discussion)
              Control0..1
              This element is affected by the following invariants: ele-1
              TypeIdentifier(NHS, HCSN and CHI Numbers)
              Is Modifierfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              68. AllergyIntolerance.patient.display
              Definition

              Plain text narrative that identifies the resource in addition to the resource reference.

              ShortText alternative for the resource
              Comments

              This is generally not the same as the Resource.text of the referenced resource. The purpose is to identify what's being referenced, not to fully describe it.

              Control0..1
              Typestring
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summarytrue
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              70. AllergyIntolerance.encounter
              Definition

              The encounter when the allergy or intolerance was asserted.

              ShortEncounter when the allergy or intolerance was asserted
              Control0..1
              TypeReference(Encounter)
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              72. AllergyIntolerance.onset[x]
              Definition

              Estimated or actual date, date-time, or age when allergy or intolerance was identified.

              ShortWhen allergy or intolerance was identified
              Control0..1
              TypeChoice of: dateTime, Age, Period, Range, string
              [x] NoteSeeChoice of Data Typesfor further information about how to use [x]
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              74. AllergyIntolerance.recordedDate
              Definition

              The recordedDate represents when this particular AllergyIntolerance record was created in the system, which is often a system-generated date.

              ShortDate first version of the resource instance was recorded
              Control0..1
              TypedateTime
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              76. AllergyIntolerance.recorder
              Definition

              Individual who recorded the record and takes responsibility for its content.

              ShortWho recorded the sensitivity
              Control0..1
              TypeReference(Practitioner, PractitionerRole, Patient, RelatedPerson)
              Is Modifierfalse
              Summaryfalse
              Alternate NamesAuthor
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              78. AllergyIntolerance.asserter
              Definition

              The source of the information about the allergy that is recorded.

              ShortSource of the information about the allergy
              Comments

              The recorder takes responsibility for the content, but can reference the source from where they got it.

              Control0..1
              TypeReference(Patient, RelatedPerson, Practitioner, PractitionerRole)
              Is Modifierfalse
              Summarytrue
              Alternate NamesSource, Informant
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              80. AllergyIntolerance.lastOccurrence
              Definition

              Represents the date and/or time of the last known occurrence of a reaction event.

              ShortDate(/time) of last known occurrence of a reaction
              Comments

              This date may be replicated by one of the Onset of Reaction dates. Where a textual representation of the date of last occurrence is required e.g. 'In Childhood, '10 years ago' the Comment element should be used.

              Control0..1
              TypedateTime
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              82. AllergyIntolerance.note
              Definition

              Additional narrative about the propensity for the Adverse Reaction, not captured in other fields.

              ShortAdditional text not captured in other fields
              Comments

              For example: including reason for flagging a seriousness of 'High Risk'; and instructions related to future exposure or administration of the substance, such as administration within an Intensive Care Unit or under corticosteroid cover. The notes should be related to an allergy or intolerance as a condition in general and not related to any particular episode of it. For episode notes and descriptions, use AllergyIntolerance.event.description and AllergyIntolerance.event.notes.

              Control0..*
              TypeAnnotation
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              84. AllergyIntolerance.reaction
              Definition

              Details about each adverse reaction event linked to exposure to the identified substance.

              ShortAdverse Reaction Events linked to exposure to substance
              Control0..*
              TypeBackboneElement
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              86. AllergyIntolerance.reaction.id
              Definition

              Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

              ShortUnique id for inter-element referencing
              Control0..1
              Typestring
              Is Modifierfalse
              XML FormatIn the XML format, this property is represented as an attribute.
              Summaryfalse
              88. AllergyIntolerance.reaction.extension
              Definition

              May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.

              ShortAdditional content defined by implementations
              Comments

              There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

              Control0..*
              TypeExtension
              Is Modifierfalse
              Summaryfalse
              Alternate Namesextensions, user content
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
              90. AllergyIntolerance.reaction.modifierExtension
              Definition

              May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.

              Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).

              ShortExtensions that cannot be ignored even if unrecognized
              Comments

              There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

              Control0..*
              TypeExtension
              Is Modifiertrue because Modifier extensions are expected to modify the meaning or interpretation of the element that contains them
              Summarytrue
              Requirements

              Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

              Alternate Namesextensions, user content, modifiers
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              ext-1: Must have either extensions or value[x], not both (extension.exists() != value.exists())
              92. AllergyIntolerance.reaction.substance
              Definition

              Identification of the specific substance (or pharmaceutical product) considered to be responsible for the Adverse Reaction event. Note: the substance for a specific reaction may be different from the substance identified as the cause of the risk, but it must be consistent with it. For instance, it may be a more specific substance (e.g. a brand medication) or a composite product that includes the identified substance. It must be clinically safe to only process the 'code' and ignore the 'reaction.substance'. If a receiving system is unable to confirm that AllergyIntolerance.reaction.substance falls within the semantic scope of AllergyIntolerance.code, then the receiving system should ignore AllergyIntolerance.reaction.substance.

              ShortSpecific substance or pharmaceutical product considered to be responsible for event
              Comments

              Coding of the specific substance (or pharmaceutical product) with a terminology capable of triggering decision support should be used wherever possible. The 'code' element allows for the use of a specific substance or pharmaceutical product, or a group or class of substances. In the case of an allergy or intolerance to a class of substances, (for example, "penicillins"), the 'reaction.substance' element could be used to code the specific substance that was identified as having caused the reaction (for example, "amoxycillin"). Duplication of the value in the 'code' and 'reaction.substance' elements is acceptable when a specific substance has been recorded in 'code'.

              Control0..1
              BindingFor example codes, see SubstanceCode
              (example to http://hl7.org/fhir/ValueSet/substance-code)

              Codes defining the type of the substance (including pharmaceutical products).

              TypeCodeableConcept
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              94. AllergyIntolerance.reaction.manifestation
              Definition

              Clinical symptoms and/or signs that are observed or associated with the adverse reaction event.

              ShortClinical symptoms/signs associated with the Event
              Comments

              Manifestation can be expressed as a single word, phrase or brief description. For example: nausea, rash or no reaction. It is preferable that manifestation should be coded with a terminology, where possible. The values entered here may be used to display on an application screen as part of a list of adverse reactions, as recommended in the UK NHS CUI guidelines. Terminologies commonly used include, but are not limited to, SNOMED CT or ICD10.

              Control1..*
              BindingFor example codes, see SNOMEDCTClinicalFindings
              (example to http://hl7.org/fhir/ValueSet/clinical-findings)

              Clinical symptoms and/or signs that are observed or associated with an Adverse Reaction Event.

              TypeCodeableConcept
              Is Modifierfalse
              Summaryfalse
              Alternate NamesSymptoms, Signs
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              96. AllergyIntolerance.reaction.description
              Definition

              Text description about the reaction as a whole, including details of the manifestation if required.

              ShortDescription of the event as a whole
              Comments

              Use the description to provide any details of a particular event of the occurred reaction such as circumstances, reaction specifics, what happened before/after. Information, related to the event, but not describing a particular care should be captured in the comment field. For example: at the age of four, the patient was given penicillin for strep throat and subsequently developed severe hives.

              Control0..1
              Typestring
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summaryfalse
              Alternate NamesNarrative, Text
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              98. AllergyIntolerance.reaction.onset
              Definition

              Record of the date and/or time of the onset of the Reaction.

              ShortDate(/time) when manifestations showed
              Control0..1
              TypedateTime
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              100. AllergyIntolerance.reaction.severity
              Definition

              Clinical assessment of the severity of the reaction event as a whole, potentially considering multiple different manifestations.

              Shortmild | moderate | severe (of event as a whole)
              Comments

              It is acknowledged that this assessment is very subjective. There may be some specific practice domains where objective scales have been applied. Objective scales can be included in this model as extensions.

              Control0..1
              BindingThe codes SHALL be taken from AllergyIntoleranceSeverity
              (required to http://hl7.org/fhir/ValueSet/reaction-event-severity|4.0.1)

              Clinical assessment of the severity of a reaction event as a whole, potentially considering multiple different manifestations.

              Typecode
              Is Modifierfalse
              Primitive ValueThis primitive element may be present, or absent, or replaced by an extension
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              102. AllergyIntolerance.reaction.exposureRoute
              Definition

              Identification of the route by which the subject was exposed to the substance.

              ShortHow the subject was exposed to the substance
              Comments

              Coding of the route of exposure with a terminology should be used wherever possible.

              Control0..1
              BindingFor example codes, see SNOMEDCTRouteCodes
              (example to http://hl7.org/fhir/ValueSet/route-codes)

              A coded concept describing the route or physiological path of administration of a therapeutic agent into or onto the body of a subject.

              TypeCodeableConcept
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))
              104. AllergyIntolerance.reaction.note
              Definition

              Additional text about the adverse reaction event not captured in other fields.

              ShortText about event not captured in other fields
              Comments

              Use this field to record information indirectly related to a particular event and not captured in the description. For example: Clinical records are no longer available, recorded based on information provided to the patient by her mother and her mother is deceased.

              Control0..*
              TypeAnnotation
              Is Modifierfalse
              Summaryfalse
              Invariantsele-1: All FHIR elements must have a @value or children (hasValue() or (children().count() > id.count()))