Allergen Class Extension

Canonical	../StructureDefinition/nexus-allergen-class-extension
Status	draft · 1.26.0
Base	Extension (constraint)
Context	AllergyIntolerance (element)
Source	FSH · JSON

What kind of thing the recorded allergen is: a single drug, a drug class, a food, an environmental substance or a vaccine.

Overview

It determines category, and says the thing category cannot. Every value here maps onto exactly one of R4's four AllergyIntolerance.category values, and two of them -- drug and class -- map onto the same one. That collision is the point: a reaction recorded against one medicinal substance and a reaction recorded against a whole family of them are both medication, and a cross-sensitivity check against a new prescription needs to know which it is reading.

It is a fact about the record, not a translation of the substance. AllergyIntolerance.code carries WHAT the patient reacted to, and every coding in it says that same thing in a different vocabulary. This says WHAT KIND, which is a different and coarser statement, so it rides an element of its own.

At most one per record. A record whose substance carries several codings still describes one allergen and therefore one class.

MIGRATION. Write this extension. Records written before it exists carry the class as an additional coding inside AllergyIntolerance.code.coding, under the same code system; that carriage is not part of this specification and is not produced going forward. A reader of older records has to read it from where it was written, and must not mistake it for a translation of the substance while doing so. Moving the existing data is outstanding work and is not described here.

Terminology bindings

Path	Strength	Value set
Extension.value[x]	required	Allergen Class Value Set