Variability in total serum IgE over 1year in severe asthmatics

BackgroundImmunoglobulin E (IgE) is the treatment target of omalizumab, a monoclonal antibody indicated in the treatment of severe allergic asthma. Long-term variability of serum total IgE (sIgE(tot)) in asthmatics remains poorly documented.MethodsIn this prospective study, sIgE(tot) levels were measured over 1year at 7 time points in 41 severe asthmatics treated with high-dose of inhaled corticosteroids and long-acting (2) agonists. 33 patients were atopic based on at least one positive RAST to common aeroallergens. Patients were divided into three groups according to their baseline sIgE(tot) level: low (<76IU/mL; n=10), intermediate (76-700IU/mL; n=20) or high (>700IU/mL; n=11). Patients also completed the six-item Juniper Asthma Control Questionnaire (ACQ(6)). The sIgE(tot) variability and factors predictive for this variability were studied, as well as ACQ(6) outcomes.ResultsThe variation in sIgE(tot) level was mostly the consequence of between patient-variability, which represented 96%, 71% and 96% of the total variability in the low, intermediate and high sIgE(tot) subgroups, respectively. The residual within-patient variability was therefore limited. In 10/41 patients, sIgE(tot) levels increased or decreased, for at least one visit, beyond the predefined range of the subgroups to which they were assigned (<76IU/mL; 76-700IU/mL;>700IU/mL). There was a significant but weak correlation between sIgE(tot) and ACQ(6) score over all time points (r=0.15, p=0.02), but sIgE(tot) failed to associate with severe exacerbation. sIgE(tot) decreased by 3% with any additional year of age for the whole group (p=0.01) and increased by 5% per one unit of allergen exposure score in atopic patients (p=0.002).ConclusionIn severe asthmatics, limited within-patient variability of sIgE(tot) levels was observed over 1year as opposed to marked between-subject variability. sIgE(tot) decreases with age. Variation in sIgE(tot) weakly associates with asthma control but not with exacerbation.