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Although the term “allergy” is generally defined as occurring via an immunologic process caused by a misdirected humoral immune response especially involving IgE antibodies or a cell-mediated process, proving this through testing is often not possible, especially for drugs. Most physicians and patients tend to conflate true drug allergy with pseudoallergy (non-allergic hypersensitivity) or interpret allergy more broadly as any adverse drug effect and documentation in EHRs often reflects this uncertainty. For this reason, standards such as HL7® FHIR® and ICD-11 combine the word allergy with allergy-like/clinically resembling allergy and do not distinguish allergy from non-allergic hypersensitivity, which would most closely align with the SNOMED concept, 473010000 |Hypersensitivity condition (finding)| and its disposition and reaction subconcepts.

Allergy list

Allergy or intolerance can be recorded in a specific section (e.g., “Drug Allergy and Intolerance”) of the EHR, which records the causative agent together with other details, including type (allergy, non-allergic hypersensitivity, intolerance), certainty, manifestation, and severity. This corresponds to the FHIR substance based AllergyIntolerance resource data model.

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Records of allergy to multiple substances or to multi-ingredient products should be recorded at the product level and updated when more specific information becomes available (e.g., positive sensitivity test to one specific ingredient of the mix).

Problem list

Allergy or intolerance can also be recorded in the EHR as a problem. The problem list is normally restricted to SNOMED CT concepts from three hierarchies – Clinical finding, Event and Finding with explicit context. This corresponds either to the FHIR finding based AllergyIntolerance resource data model or the FHIR Condition resource.

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To record the level of certainty or verification status, it is recommended to use additional data elements in the EHR information model. Even though it is possible to utilize the SNOMED CT model for ‘situation with explicit context’ to express certainty, this is not recommended due to potential ambiguity. For example, “suspected penicillin allergy” can mean uncertainty with the condition (is it real allergy?) or with the causative agent (is it penicillin?). Even though SNOMED CT editorial guideline is clear that the first interpretation is correct, it is better to use other methods to represent the uncertainty to avoid confusion.

Documentation of Allergy Desensitization

Desensitization (aka hyposensitization) therapy involves the administration of increasing doses of an allergen in order to induce a state of tolerance. Desensitization to inhalant and food allergens (allergen immunotherapy) results in long-term control of symptoms, which may persist after the treatment is discontinued, while drug desensitization induces temporary tolerance only during the course of therapy. In either case, an active status of allergy should not be removed from the medical record in those patients that are undergoing or have completed a course of desensitization therapy. Documentation of patients undergoing specific desensitization protocols using SNOMED CT can be accomplished using the descendants of 367428009 |Desensitization therapy (regime/therapy).

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