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

Abstract In addition to contribution from environmental factors, overdiagnosis has been postulated as a cause for increasing incidence of acute allergic reactions (AAR) and anaphylaxis in the last few decades. This study focussed on population trends with the aim of identifying pointers to overdiagnosis in AAR and anaphylaxis in the emergency department (ED). The study analyzed administrative data on ED visits in Calgary, Canada between 2010 and 2019. The primary outcome of interest was the change in ED visit rates of AAR and anaphylaxis over the study period. Secondary outcomes consisted of indices of severity including inpatient admissions and ED length of stay. 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. This study reports a significant increase in ED visit rates for anaphylaxis (0.14% of ED visits in 2010 vs 0.25% in 2019; P < 0.001) but AAR ED visits remained unchanged (0.99% of ED visits in 2010 vs 1.03% in 2019, P = 0.079). No significant change was observed in severity indices for AAR and anaphylaxis. 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 of 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 potential for patient harm.