[Utility of serum tryptase in Emergency Department patients with possible anaphylaxis]

Background Diagnosing anaphylaxis is often straightforward but can be challenging if the presentation is atypical. In patients with atypical symptoms suspected to be due to an acute allergic reaction, s-tryptase can give additional diagnostic information. Measuring s-tryptase is also helpful in diagnosing mastocytosis. Obtaining s-tryptase levels has been done in the emergency department (ED) at Landspitali since 2011. The aim of this study was to evaluate the benefit of obtaining s-tryptase levels in the ED. Methods With institutional review board approval, all cases where s-tryptase level was obtained in ED patients from 2011-2018 were retrospectively reviewed. A database was collected including information on patient demographics, presenting symptoms, treatment, diagnosis, s-tryptase level and follow up. Results A total of 214 patients had a s-tryptase level measured. Serum tryptase was elevated (>12 μg/L) in 36 cases. Females were 131 and average age 40.6 years. Of the patients, 86.4% had skin or mucosal symptoms, 48.1% cardiovascular symptoms, 49.5% respiratory symptoms and 36.0% had gastrointestinal symptoms. An allergist reviewed 126 returning patients and 65 were considered to have had an episode of anaphylaxis. Of those 65 were 4 patients which did not meet the diagnostic criteria for anaphylaxis but had raised s-tryptase levels. Sensitivity of s-tryptase measurement was 40.9% and specificity 97.1%. Conclusions Obtaining a s-tryptase level from ED patients with possible anaphylaxis seems to be useful in atypical cases. The measurement is specific but not sensitive. No cases of mastocytosis were identified in the patient cohort.