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FARE Blog June 22, 2021

Biphasic Reactions Are More Likely When Symptoms of Initial Reaction Are Severe

Researchers use data from the FARE Patient Registry to investigate a subset of allergic reactions to food in which symptoms subside for an hour or more and then return.

Emergency Sign

A biphasic reaction to food happens when a person with food allergy:

  1. is exposed to their problem food
  2. reacts to the food with symptoms that resolve, either with or without treatment (initial reaction)
  3. develops reaction symptoms again more than an hour later without being exposed to the food a second time (secondary reaction)

Most reports on the incidence of biphasic reactions come from oral food challenges. These incidences vary widely, from one biphasic reaction for every 100 reactions to one biphasic reaction per every five reactions.

Wanting to learn more about biphasic reactions that happen outside the clinical setting, researchers at Northwestern University looked at data from the FARE Patient Registry. Published in the Journal of Allergy and Clinical Immunology: In Practice, their study evaluated the experiences of Registry participants whose most recent food-related allergic reaction reported to the Registry was biphasic.

Reactions were reported to the Registry by, or on behalf of, nearly 3,800 participants. Individuals who are white (82 percent), male (61 percent) and under age 18 (60 percent) are overrepresented among Registry participants. Researchers report the following findings:

  • The incidence of biphasic reactions among Registry participants was 16 percent. Biphasic reactions were more likely to be self-reported by an allergic adult (21 percent) than reported by the parent or guardian of an allergic child (13 percent).
  • Severe initial reactions were associated with increased risk of developing a secondary reaction. When the initial reaction was mild, only 7 percent of participants reported that their symptoms resolved and then returned, but when the initial reaction was described as very severe, a full 30 percent of participants reported the return of symptoms.
  • Among biphasic reactions, the severity of the initial reaction corresponded to the severity of the secondary reaction. Mild initial reactions typically preceded mild (52 percent) or moderate (42 percent) secondary reactions, while very severe initial reactions were associated with severe (32 percent) or very severe (43 percent) secondary reactions.
  • Peanut, tree nuts, milk and egg were the culprit food that most commonly triggered biphasic reactions. These are also, in descending order, the four food allergies most commonly reported to the Registry.
  • During most of the biphasic reactions reported to the Registry, epinephrine was not given to treat the initial reaction. Initial reactions in children were much more likely to be treated with epinephrine (40 percent) than initial reactions in adults (22 percent).

To learn more about joining the FARE Patient Registry and contributing to research studies like this one, visit foodallergy.org/registry.

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