Defines the Nexus EMR standard for AllergyIntolerance resources, based on CA-Core+. Includes instance-specific Nexus EMR identifiers, references via identifier (CII E01).
Salient fields
The profile's synthesized-accessor contract: fields TypedFhir surfaces as first-class typed properties, each computed from the instance by a restricted FHIRPath expression. See Salient Fields for what they are, how they shape LLM contexts, and how to declare them.
The substance or class of substances that the patient has an allergy or intolerance to.
REQUIRED: text element for human readability
RECOMMENDED, for a DRUG allergen: an ingredient-level code in the slices below. CCDD is
preferred; where the source has no CCDD -- in practice most legacy EMR allergy lists -- the
Health Canada DPD active-ingredient group number is the one to carry, with ATC for class-level
records. That code is the only thing making an allergen joinable to a medication record;
without it an allergy and a prescription share nothing but free text.
OPTIONAL: SNOMED CT for non-drug allergens (foods, environmental substances) and for
substance classes
OPTIONAL: Raw EMR allergen codes for source system preservation
Nexus EMR does not mandate a specific coding system for allergens.
The text element ensures human readability even when coded values are not recognized.
Where this code was mapped from a source system's own vocabulary, carry the raw coding alongside the mapped one, flagged userSelected = true. See Carrying the raw code.
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.
The clinical status of the allergy or intolerance. Used to distinguish active allergies from historical or resolved ones. Present on every allergy except a retracted one: R4's ait-1 requires it unless verificationStatus is entered-in-error, and ait-2 forbids it when that is the status.
Comments
This is a modifier element - absence of an active status means the allergy should not trigger alerts. Absence because the entry is entered-in-error means the allergy was never true and must not be surfaced at all, which is a different statement from inactive or resolved.
Assertion about certainty associated with the propensity, or potential risk, of a reaction to the identified substance (including pharmaceutical product).
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.
Whether the reaction is immune-mediated (allergy) or not (intolerance)
Definition
Identification of the underlying physiological mechanism for the reaction risk.
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.
The risk that a future exposure causes serious harm
Definition
Estimate of the potential clinical harm, or seriousness, of the reaction to the identified substance.
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.
Clinical symptoms and/or signs that are observed or associated with the adverse reaction 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.