Incidence and timing of biphasic anaphylactic reactions: a retrospective cohort study

We investigated the frequency of overall biphasic reactions, biphasic reactions that met the diagnostic criteria of anaphylaxis, and biphasic reactions that caused a severe abnormality in vital signs in patients who visited the emergency department of a tertiary hospital.

This retrospective cohort study included patients aged 18 years or over who presented with anaphylaxis at the emergency department of a tertiary care hospital between January 2014 and December 2016. The primary outcome was the incidence of biphasic reactions that caused a severe abnormality in vital signs and developed within 7 days. Secondary outcomes were the frequency of overall biphasic reactions and those that met the diagnostic criteria of anaphylaxis.

In total, 437 patients aged over 18 years visited the emergency department during the study period. Among them, 202 were enrolled in this study. The proportion of patients who had overall biphasic reactions, those that met the diagnostic criteria of anaphylaxis, and those with a severe abnormality in vital signs was 8.9%, 3.0%, and 1.0%, respectively. Overall, 32.7% of patients were hospitalized, but hospitalization aided in the treatment of severe biphasic reactions at the early stage in only one patient.

We found that 8.9% of adult patients with anaphylaxis had a biphasic reaction, but biphasic reactions together with severe abnormalities in vital signs were rare.