Describes an observation of an "Intolerance Condition" of the Patient. Intolerance Conditions are typically allergies, but the concept of an intolerance condition is broader than just allergies. For example, an adverse reaction such as the patient becomes nauseous after taking a particular antibiotic is not an allergy, but may serve as a contra-indicator to the use of that antibiotic. In general, Intolerance Conditions as caused by Food, Drugs, or some environmental factor such as mold, insect venom (i.e., bee stings), or pet dander.

A collection of Intolerance Condition (aka Allergy) records. This class represents the traditional "Allergy List" that is used to inform the Provider of substances that should likely be avoided when treating the Patient.

Reaction: "A response to a substance, treatment, or other stimulus, such as an antigen-antibody reaction, an allergic reaction, or an adverse pharmacological reaction." - Mosby's Medical Dictionary This class documents an Observation of an adverse physiological response attributed to the exposure of the Patient to the given substance. Note that the dates may be unspecified, such as when the Patient reports that she breaks out in hives when she eats peanuts. "Details about each adverse reaction event linked to exposure to the identified substance." - HL7 FHIR, AllergyIntolerance.reaction

This class documents an Observation (i.e., a test) performed in order to confirm (or refute) the sensitivity, and/or to determine the mechanism of the sensitivity.