3.4. Sensitivity and specificity
The results of the MSD multiplex immunoassay were compared to the
results of the ImmunoCAP assay and the SPT. The sensitivity and
specificity of the MSD multiplex immunoassay were calculated (Table 3).
Overall, the sensitivity of the MSD multiplexed assay was high for most
allergens compared to the SPT and ImmunoCAP assay as references (≥75%),
however, for some sIgEs the sensitivity values were lower. As described
above, dust mite allergy was not always detected using MSD (sensitivity:
60%). Furthermore, the sensitivity of the MSD assay detecting sIgE
against dog epithelium and mugwort was low when using the ImmunoCAP
assay as reference (20-50%), but was very good (100%) in comparison
with SPT. Since the SPT is still used as the golden standard in clinical
practice, the MSD multiplex immunoassay for dog and mugwort allergies
was considered sensitive. It seemed that the ImmunoCAP assay was more
sensitive to dog and mugwort allergens, which may have indicated that
the individuals were sensitized without clinical signs of allergy. For
some sIgEs, the sensitivity could not be determined, due to a lack of
positive individuals for these allergies (Figure 1). In contrast to the
sensitivity, the specificity of the MSD multiplex immunoassay was very
high (≥80% - with the majority showing 100% specificity). When using
the data from the SPT as reference, the only sIgE with low specificity
was rye (25%). This was probably due to cross-reactivity of IgE
antibodies against timothy grass and rye, both species of grasses of thePoaceae family.17 The cross-reactivity caused a
person allergic to timothy grass, to also test positive for sIgE against
rye in the MSD multiplex immunoassay and the ImmunoCAP assay. However,
the SPT showed only an allergic reaction to timothy grass (Figure 1). A
limitation of this study was the fact that, for the ImmunoCAP assay,
only results of three mixtures of allergens were available and could be
compared, and only one mixture was available for parallel tests in the
SPT (Table 1).
In previous studies, the sensitivity and specificity of the ImmunoCAP
assay were compared to the golden standard, the
SPT.18,19 For a select set of allergens that were
analysed both in those previous studies with the ImmunoCAP assay and
with the MSD multiplex immunoassay in the current study, similar
sensitivity and specificity were observed (Table S2). For timothy grass,
cats and dogs, the MSD multiplex immunoassay showed higher sensitivity
and specificity values than the ImmunoCAP assay when compared to the
SPT. The specificity values of dust mite and Cladosporium
herbarum were also higher for the MSD multiplex immunoassay, however,
the sensitivity of dust mite and the specificity of rye were higher in
the ImmunoCAP assay.