The following is a summary of the “Biphasic Allergic Reactions at a Dutch Emergency Department: A 5-Year Retrospective Cohort Study,” published in the  January 2023 issue of Emergency Medicine by Zwet, et al.

Only about 0.4% to 20% of people with an allergic reaction have a biphasic reaction, and we don’t know how often severe biphasic reactions occur. Therefore, they aimed to examine a cohort of Dutch ED patients to determine the frequency and onset of clinically significant biphasic reactions. Additionally, average observation times post-ED visit for allergy-related symptoms were calculated, and patient characteristics of those who experienced a biphasic reaction were evaluated.

The participants lived in the same area, so this study was a retrospective cohort study. Between January 2015 and December 2019, they gathered information from the medical records of adults who sought emergency care for an allergic reaction. Clinically significant biphasic reactions were defined as those that met the criteria for anaphylaxis. There were a total of 557 patients in the study. Around 8 patients (1.4% of the total included) experienced a biphasic reaction, with only 1 case being clinically significant. Among the subset of patients who experienced anaphylaxis (n = 258), those figures were 2.3% and 0.4%. 

Biphasic allergic reactions occurred on average 25.4 hours after the onset of the initial allergic reaction (95% CI, 13.2–37.6 hours). The single biphasic reaction with clinical significance occurred 30 hours after the initial reaction. Their cohort had a small number of patients who experienced clinically significant biphasic reactions, and the average time between the initial allergic reaction and the biphasic reaction was > 24 hours. These retrospective data from a single center suggest that long-term in-hospital monitoring may not be necessary for all patients.

Source: sciencedirect.com/science/article/abs/pii/S0736467922005753