Fatal Anaphylaxis to Yellow Jacket Stings in Mastocytosis: Options for Identification and Treatment of At-Risk Patients

Background Patients with indolent systemic mastocytosis (ISM) are at risk for severe anaphylactic reactions to yellow jacket (YJ) stings while demonstration of sensitization can be challenging because specific IgE (sIgE) levels are regularly below 0.35 kUA /L. The implication of missing YJ allergy is illustrated by a case of fatal anaphylaxis. Objective To explore the natural course of YJ venom allergy and the diagnostic accuracy and therapeutic consequence of YJ venom sIgE in patients with ISM. Methods All patients with ISM seen from 1981 to 2015 (n = 243) were evaluated on the number of YJ stings, reaction severity, and sensitivity and specificity of YJ venom sIgE. YJ venom allergic patients without mastocytosis served as control (n = 313). Results A total of 153 patients with ISM were stung during adult life. The first systemic reaction was more often severe in patients with ISM than in patients without mastocytosis (69.9% vs 22.0%) and reactions recurred in 40 of 41 re-stung patients with ISM. ISM reactors showed lower YJ venom sIgE levels than nonmastocytosis reactors (0.61 vs 4.83 kUA /L; P < .001) and asymptomatic sensitization was exceedingly rare. In ISM the current clinical threshold of 0.35 kUA /L yields a sensitivity and specificity of 77.6% and 87.5%, respectively. The optimal diagnostic accuracy is achieved at 0.17 kUA /L (sensitivity, 83.6%; specificity, 85.0%). Conclusions The high rate of severe reactions and the fatal case underscore the importance of adequate diagnostic sensitivity of sIgE in patients with ISM. The sensitivity of sIgE can be ameliorated by lowering the threshold to 0.17 kUA /L, retaining good specificity. We recommend sIgE screening in all patients with ISM and discussing immunotherapy when YJ venom sIgE exceeds 0.17 kUA /L.