Biphasic Allergic Reactions at a Dutch Emergency Department: A 5-Year Retrospective Cohort Study

A biphasic allergic reaction develops in 0.4-20% of patients with an allergic reaction, but the incidence of severe biphasic reactions is unknown OBJECTIVE: Our objective was to assess the incidence and time of onset of clinically relevant biphasic reactions in a Dutch emergency department (ED) cohort. Furthermore, the characteristics of patients with a biphasic reaction and the mean observation time after an allergy-related ED visit were assessed.

This was a single-center retrospective cohort study. We collected data from clinical records of adult patients presenting with an allergic reaction to the ED between January 2015 and December 2019. We defined clinically relevant biphasic reactions as biphasic reactions in which the criteria for anaphylaxis were met.

Five hundred fifty-seven patients were included. Eight patients (1.4%) developed a biphasic reaction, of which 1 (0.2% of the total inclusions) was clinically relevant. In the subgroup of patients with an anaphylactic reaction (n = 258), those percentages were 2.3% and 0.4%, respectively. The mean time between the initial allergic reaction and the biphasic allergic reaction was 25.4 h (95% CI 13.2-37.6 h). The single clinically relevant biphasic reaction occurred 30 h after the initial reaction.

The incidence of clinically relevant biphasic reactions in our cohort was low, with a mean time between the initial allergic reaction and the biphasic reaction of > 24 h. Based on these single-center retrospective data, routine inpatient monitoring for several hours does not seem warranted for all patients.