Incidence of clinically important biphasic reactions in emergency department patients with allergic reactions or anaphylaxis.
OBJECTIVE
Allergic reactions are common presentations to the emergency department (ED). An unknown proportion of patients will develop biphasic reactions, and patients are often monitored for prolonged periods to manage potential reactions. We seek to determine the incidence of clinically important biphasic reactions.


METHODS
Consecutive adult patients presenting to 2 urban EDs with allergic reactions during a 5-year period were identified. Encounters were dichotomized as "anaphylaxis" or "allergic reaction" with an explicit algorithm. A comprehensive chart review was conducted on each index and all subsequent visits to detail patient presentations, comorbidities, ED management, and predefined clinically important biphasic reactions. Regional and provincial databases were linked to identify subsequent ED visits and deaths within a 7-day period. The primary outcome was the proportion of patients with a clinically important biphasic reaction, and the secondary outcome was mortality.


RESULTS
Of 428,634 ED visits, 2,819 (0.66%) encounters were reviewed (496 anaphylactic and 2,323 allergic reactions). Overall, 185 patients had at least 1 subsequent visit for allergic symptoms. Five clinically important biphasic reactions were identified (0.18%; 95% confidence interval [CI] 0.07% to 0.44%), with 2 occurring during the ED visit and 3 postdischarge. There were no fatalities (95% CI 0% to 0.17%). In the anaphylaxis and allergic reaction groups, clinically important biphasic reactions occurred in 2 patients (0.40%; 95% CI 0.07% to 1.6%) and 3 patients (0.13%; 95% CI 0.03% to 0.41%), respectively.


CONCLUSIONS
Among ED patients with allergic reactions or anaphylaxis, clinically important biphasic reactions and fatalities are rare. Our data suggest that prolonged routine monitoring of patients whose symptoms have resolved is likely unnecessary for patient safety.
Department of Emergency Medicine, University of British Columbia, Vancouver, British Columbia, Canada; St. Paul's Hospital, Vancouver, British Columbia, Canada. Electronic address: briangrunau@gmail.com.
Brian E
BE
Grunau
Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
Jennifer
J
Li
Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
Tae Won
TW
Yi
Department of Emergency Medicine, University of British Columbia, Vancouver, British Columbia, Canada; School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada; St. Paul's Hospital, Vancouver, British Columbia, Canada.
Robert
R
Stenstrom
Department of Emergency Medicine, University of British Columbia, Vancouver, British Columbia, Canada; St. Paul's Hospital, Vancouver, British Columbia, Canada.
Eric
E
Grafstein
School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, Canada.
Matthew O
MO
Wiens
Division of Allergy and Immunology, University of British Columbia, Vancouver, British Columbia, Canada; St. Paul's Hospital, Vancouver, British Columbia, Canada.
R Robert
RR
Schellenberg
Department of Emergency Medicine, University of British Columbia, Vancouver, British Columbia, Canada; St. Paul's Hospital, Vancouver, British Columbia, Canada.
Frank Xavier
FX
Scheuermeyer
D000328:Adult; D000707:Anaphylaxis / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology / Q000628:therapy; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology / Q000628:therapy; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013997:Time Factors