Introduction
Determination of specific IgE (sIgE) is one of the pillars on which allergy diagnosis stands, together with anamnesis, skin tests and allergen challenges (1, 2). IgE sensitization is commonly demonstratedin vivo by skin prick testing (SPT), or in vitro utilizing automated systems. IgE sensitization is commonly demonstrated in vivo by skin prick testing (SPT), or in vitro utilizing automated systems. Because IgE concentrations are very low in peripheral blood (3), very sensitive methods for sIgE measurement have been developed, such as ImmunoCAP (Thermo Fisher Scientific, Uppsala, Sweden), which has been in use for more than 30 years and is currently considered as the reference method (4, 5). Accurate determination of sIgE concentrations is hampered by many factors such as variations in the composition of the allergenic sources (6), diversity of physico-chemical methods used to prepare allergen extracts, possible competition by non-IgE anti-allergen antibodies (7, 8), unwanted reactivity with clinically irrelevant cross-reactive carbohydrate determinants (CCD) (9), and lack of result standardization (10). Initially developed to quantitate sIgE capable of binding to allergenic extracts, which are complex mixtures of proteins, contemporary sIgE assays also measure sIgE to a variety of individual allergenic molecules, called molecular allergens (MA) (11). In daily practice, the impact of these tests has been restricted to the correct identification of allergen(s) responsible for clinical symptoms and to the estimation of the risk of severe reactions, deduced from the sensitization profile against MA (12-14). A commonly accepted rule is that, isolated from the clinical context, sIgE values cannot discriminate between sensitization and allergy. The capacity of sIgE values to “predict” the presence or absence of allergy symptoms as a function of the degree of sensitization is thus constrained by interindividual variations and the presence of co-factors (e.g. exercise, medication, concomitant infection, etc). Determination of useful sIgE threshold values, in particular for food allergens, was previously attempted in many studies using ImmunoCAP tests and demonstrated a general lack of agreement for these values (15).
In the last three years, new contenders, like NOVEOS (Hycor, Garden Grove, CA, USA), have started to propose new methods of sIgE measurement. NOVEOS uses biotinylated soluble allergens coupled to streptavidin-coated magnetic beads and thus, diverge from ImmunoCAP, which is based on allergens bound to a cellulose matrix and fluorescence signal. NOVEOS differs also from ImmunoCAP by requiring a lower test sample volume of 4 µL, versus 40 µL.
So far, only two reports have compared analytical performances of NOVEOS and ImmunoCAP, and only for airborne allergens. The first study compared sIgE results for 21 airborne allergens (9 extracts and 12 MA) on samples from 368 patients (16) and found a good overall correlation (Spearman’s rho: 0.65-0.96 for extracts; 0.79-0.98 for MA). The second report compared sIgE reactivity against two mixtures of airborne allergens, ImmunoCAP Phadiatop and NOVEOS SX01, on a cohort of 1314 pediatric samples. Spearman’s correlation between the data set of both methods was 0.84 (17).
However, comparison of the clinical performance of the two methods has not been addressed yet, and data for food allergens is lacking. The main objective of this study was to determine whether the theoretical technical advantages of NOVEOS technology can be translated into an equivalent or superior performance to that of ImmunoCAP, in a clinical setting of food allergy.