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.