17 Disparity in rates and severity of emergency department visits for acute allergic reactions and anaphylaxis over a decade in Calgary: signal for overdiagnosis

Objectives The incidence of acute allergic reactions (AAR) and anaphylaxis has increased in the last few decades. In addition to the contribution from environmental factors, overdiagnosis, stemming from the broadening of diagnostic criteria, has been postulated as a cause. There is a paucity of research on overdiagnosis in AAR and anaphylaxis in emergency departments (ED) and to the best of the knowledge of the researchers, this is a novel study on overdiagnosis in anaphylaxis in the ED. This study explored population trends with the aim of identifying pointers to overdiagnosis in the observed changes in the incidence and severity of AAR and anaphylaxis. Methods This study retrospectively analyzed aggregate administrative data on ED visits in Calgary, Canada between 2010 and 2019. ED visits with a primary discharge diagnosis of anaphylaxis and or AAR were included. The primary outcome of interest was the change in ED visit rates over the study period. Secondary outcomes consisted of indices of severity including the percentage of patients with anaphylaxis requiring admission (acute and intensive care), median ED length of stay (LOS), and the mean Canadian Triage and Acuity Scale (CTAS) score. Changes in ED visit rates and severity indices were assessed with a time trend analysis using linear regression of age- and sex-standardized rates adjusted for population growth. P values of less than 0.05 were accepted as statistically significant. Results During the study period, 37,446 (1.05%) and 7,200 (0.2%) of 3,557,839 total ED visits were due to AAR and anaphylaxis, respectively. There was a statistically significant increase in ED visit rates for anaphylaxis over the study period (0.14% of ED visits in 2010 vs 0.25% in 2019; R2=0.66, P<0.001), while no significant change was observed in AAR ED visits (0.99% of ED visits in 2010 vs 1.03% in 2019; R2=0.02, P=0.079). No significant change was observed in severity indices for anaphylaxis visits including inpatient admissions (21 vs. 29 visits per 1000; R2=0.11, P=0.354), ED LOS (2.8 vs. 2.7 hours; R2<0.01, P=0.906), and CTAS score (1.86 vs. 1.83; R2<0.01, P=0.981). Conclusions Over the study period, an increase in the rate of anaphylaxis was observed without a concomitant rise in the rate of AAR ED visits or severity of presentation. This observed disparity in the trend in the frequency of cases and severity of cases is suggestive of overdiagnosis. Clinical guidelines for AAR and anaphylaxis should carefully consider how changing diagnostic thresholds may lead to overdiagnosis and the potential for patient harm.

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