Published Online: April 3, 2014
A biphasic reaction is the recurrence of anaphylaxis symptoms within 72 hours of the initial anaphylactic event, without re-exposure to the trigger. Biphasic reactions are uncommon and unpredictable. Prior studies suggest that wheezing and delayed treatment with epinephrine may be associated risk factors.
In a study recently published in The Journal of Allergy and Clinical Immunology: In Practice, Lee and colleagues attempt to identify predictors of biphasic anaphylactic reactions in Emergency Department (ED) patients with anaphylaxis.
From April 2008 to January 2013, patients of all ages who presented to Saint Mary's Hospital ED of the Mayo Clinic, a hospital with 73,000 annual patient visits, and who met the diagnostic criteria for anaphylaxis, were consecutively included. The authors collected data on patient characteristics, suspected triggers, signs and symptoms, ED management, and disposition. Analyses were performed to estimate the association between potential predictor variables and biphasic reactions.
There were 541 patients with anaphylaxis, with a median age of 35 years (interquartile range, 18-52 years) and 59% were female. Twenty-one (4%) patients had biphasic reactions, of which 2 were pediatric patients. The median time between the resolution of initial symptoms and onset of the biphasic reaction was 7 hours (range, 1-72 hours). Biphasic reactions were associated with a history of prior anaphylaxis (odds ratio [OR] 2.6, 95% confidence interval [CI] 1.1-6.4; p=.029), an unknown precipitant (OR 2.6, 95%CI 1.1-6.2; p=.03), presenting with symptoms of diarrhea (OR 4.5, 95% CI 1.4-14.0; p=.024), and wheezing (OR 2.6, 95% CI 1.4-8.9; p=.029).
These findings underscore the need for prolonged observation in those with anaphylaxis, particularly those at increased risk as identified in this study (those having a history of prior anaphylaxis, an unknown precipitant, or those who present with symptoms of diarrhea or wheezing).
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.