“Incidence of Clinically Important Biphasic Reactions in Emergency Department Patients wit Allergic Reactions or Anaphylaxis”

Grunau BE, Li J, Yi TW, et al.

Annals of Emergency Medicine 2014; 63(6): 736-744


Background: Allergic or anaphylactic reactions are fairly common presentations to the ED.  After initial treatment and clinical improvement, a proportion of patients may develop a second “biphasic” reaction, which may actually be more severe than the initial presentation.  Because of this concern, patients are often held for observation for 6 or more hours.  This prolonged ED stay has not been shown to decrease biphasic reactions’ complications, yet incurs significant costs.  The goal of this study was to examine the incidence of clinically important biphasic reactions.

Methods: Chart review performed on data from 2 urban EDs, collected on adult patients presenting during a 5-yer period with “anaphylaxis” or “allergic reaction.”  Primary outcome was the proportion of patients with a clinically important biphasic reaction, secondary outcome was mortality.

Results: Of 428,634 ED visits, 2819 encounters (496 anaphylactic, 2323 allergic reactions) were reviewed.  185 patients had at least 1 subsequent visit for allergic symptoms.  5 clinically important biphasic reactions were identified (0.18%, 95% CI 0.07-0.44%); 2 occurred during the ED visit, and 3 were post-discharge.  2 patients with the biphasic reaction were in the anaphylaxis group (0.40%), and 3 were from the allergic reaction group (0.13%).  There were no fatalities.

Conclusion:  Clinically important biphasic reactions and fatalities were rare in ED patients presenting with allergic or anaphylactic reactions.  This study’s results suggest that it may not be necessary to conduct routine prolonged monitoring of patients whose symptoms have improved after initial treatment.

June 2024