(1) Background: Allergic reactions and angioedema are important immunologic conditions in acute care settings. Prior data indicate an association between the severity of symptoms and maximum lysis (ML) in thromboelastography. We aimed to evaluate the dynamics of ML after two hours of observation after admission to the emergency department. (2) Methods: We deter-mined ML with thromboelastography using extrinsic testing (EXTEM, ROTEM®, Werfen GmbH, Munich, Germany) at the presentation of patients with immunologic reactions and approximately two hours thereafter. The median test was used to compare the extent of ML between individuals who were still symptomatic at follow-up and those who were asymptomatic. (3) Results: We pro-spectively enrolled 16 individuals (10 (63%) female, mean age 50±14 years). Of these, 6 (38%) were still symptomatic at follow-up. Patients who had persistent symptoms had significantly higher ML than those who were asymptomatic (14% (IQR 12-17) vs. 8% (IQR 4-10), p=0.002). (4) Conclusions: ML is elevated in patients who are still symptomatic two hours after presenting to the emergency department due to an immunologic reaction.