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.