Published Online: February 14, 2015
Anaphylaxis is a serious allergic reaction that is rapid in onset and if untreated can lead to death. Biphasic anaphylaxis is the recurrence of anaphylactic symptoms within 1-72 hours—after initial symptoms have subsided—with no further exposure to the inciting trigger. Studies to date report several risk factors that may lead to a biphasic reaction. However, the size of these studies has been hindered by the rarity of the event.
In a study recently published in The Journal of Allergy and Clinical Immunology: In Practice, Lee and colleagues conducted a systematic review and meta-analysis of existing literature to elucidate the rate, time of onset, and risk factors for biphasic reactions.
Among 4,114 patients with anaphylaxis, 192 experienced biphasic reactions and were included in the meta-analysis. Biphasic reactions were seen 1 in every 20 patients. The median time of onset of biphasic reactions was 12 hours. Initial presentation with low blood pressure, and an unknown trigger, were associated with the development of a biphasic reaction.
Biphasic reactions are uncommon and often occur beyond the 6 hours of observation recommended in some anaphylaxis guidelines. As a result, identifying patients who are most likely to benefit from a longer period of observation is an important clinical question, and data from this meta-analysis suggest that patients with an unknown trigger, or those who initially present with hypotension, are at increased risk.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.