Variability in total serum IgE over 1 year in severe asthmatics

Abstract

Background: Immunoglobulin 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.

Methods: In this prospective study, sIgE_tot levels were measured over 1 year at 7 time points in 41 severe asthmatics treated with high-dose of inhaled corticosteroids and long-acting β₂ 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 (< 76 IU/mL; n = 10), intermediate (76-700 IU/mL; n = 20) or high (> 700 IU/mL; n = 11). Patients also completed the six-item Juniper Asthma Control Questionnaire (ACQ₆). The sIgE_tot variability and factors predictive for this variability were studied, as well as ACQ₆ outcomes.

Results: The 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 (< 76 IU/mL; 76-700 IU/mL; > 700 IU/mL). There was a significant but weak correlation between sIgE_tot and ACQ₆ 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).

Conclusion: In severe asthmatics, limited within-patient variability of sIgE_tot levels was observed over 1 year 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.

Keywords: Asthma; IgE; Variability.

Fig. 1

The 12-month variability in sIgE_tot in severe asthmatic patients stratified by sIgE_tot at baseline (low, intermediate and high). The 12-month variability in sIgE_tot was evaluated in 41 patients divided post hoc in three strata based on sIgE_tot at baseline: < 76 IU/mL (n = 10) (a); 76–700 IU/mL (n = 20) (c) and > 700 IU/mL (n = 11) (d). One outliner patient from the low sIgE_tot group is shown separately (b). The gray zone indicates the 76–700 IU/mL region (intermediate group) to allow for the identification of patients whose sIgE_tot reached the level of a different group during the study period

Fig. 2

Variation in sIgE_tot and asthma control in severe asthmatic patients (n = 41) according to the seasons. Data from the 6 follow-up visits are shown according to the month of the visit (the baseline data are not included). In these graphics, the geometric mean sIgE_tot with standard deviation (SD) (a) and the geometric mean six-item Juniper Asthma Control Questionnaire (ACQ₆) score with SD (b) are given