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Biphasic anaphylaxis: can I go home right after symptoms resolve?

Published online: August 3, 2020

Anaphylaxis is a very rapid and severe form of an allergic reaction most commonly to food, drug, or insect sting. Typically, anaphylaxis starts after a few (2–20) minutes following contact with the elicitor. Common symptoms are wheals, itching and skin swelling followed by shortness of breath, and/or drop of blood pressure. In the majority of cases after the reaction resolves, no subsequent reaction follows. However, in some patients the symptoms may reoccur. This course is known as biphasic anaphylaxis and is one of the main reasons why international anaphylaxis guidelines recommend observing patients in a hospital after anaphylaxis for at least 4–6 or even up to 24 hours.   

Kraft et al. in The Journal of Allergy and Clinical Immunology: In Practice used the data from the European Anaphylaxis Registry to analyze possible risk factors of this unusual course. They analyzed a cohort of 435 cases of biphasic anaphylaxis and compared them with 8,736 monophasic reactions. The data for the analysis was obtained between 2011 and 2018 in ten European countries and Brazil from patients with a history of anaphylaxis who presented for an evaluation in specialized allergy centers.

The authors found that biphasic course was more common among severe reactions with multiorgan involvement. Patients in whom the reaction was associated with exercise and who had a history of chronic urticaria had higher risk for biphasic reaction. On average 4.7% of reactions were biphasic and there were no differences between the main groups of elicitors of anaphylaxis: food, drug and insects. However, one particular elicitor, peanut (and also tree nuts but to a lesser extent), was associated with a higher rate of biphasic anaphylaxis (9.6% of the reactions to peanut were biphasic). On the contrary, anaphylaxis caused by milk was rarely biphasic.

These identified risk factors provide new insights into understanding biphasic anaphylaxis and can support clinicians in identifying which patients might need prolonged observation in a hospital following anaphylaxis.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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