Nasal specific IgE correlates to serum specific IgE: First steps towards nasal molecular allergy diagnostic
Authors: Mehmet Gökkaya, Vera Schwierzeck, Karisa Thölken, Stephan Knoch, Michael Gerstlauer, Gertrud Hammel, Claudia Traidl‐Hoffmann, Stefanie Gilles
Journal: Allergy (2020)

To the Editor, Up to 40% of the European population suffer from respiratory type I hypersensitivity reactions induced by airborne allergens, such as plant pollen, fungal spores, or dust mite feces.1 Guidelines for the treatment of AR in children recommend causative treatment, that is, allergen-specific immunotherapy (ASIT), as early as possible.2 Allergy diagnostics is routinely performed by skin prick test (SPT) or blood test for the detection of allergen-specific immunoglobulin E (sIgE). If specific serum IgE is absent despite a positive history of allergic rhinitis, a nasal allergen provocation test is performed to assess local allergic rhinitis (LAR). Recent developments in microchip technology enabled the simultaneous detection of specific IgE levels against 112 individual allergens using only 30 µL of serum. However, SPTs are still often the method of choice when diagnosing young children, as children are typically afraid of needles. This can lead to improper diagnosis, since SPTs are prone to false-positive results due to the unspecified extracts used.3 The aim of our study was therefore to adopt the Immuno Solid-phase Allergen Chip (ISAC) for nasal fluid as a noninvasive sampling method and to validate the technology as potential novel allergy test. Our analysis (see details in online supporting information) focused on the most relevant aeroallergens, that is, house dust mite (HDM), Betulaceae trees, including birch, hazel and alder, and grass pollen.4 Blood and nasal fluid samples as previously described 5 were obtained from 2 nonsensitized (NS) control subjects and 47 subjects sensitized (Figure S1and Table S2. online supporting information) to aeroallergens such as birch, hazel, alder, grass pollen, or house dust mite (HDM). Specific IgE levels were measured in sera and nasal fluid by the ImmunoCAP ISAC 112 (Table S1. online supporting information) according to the manufacturer's instruction (Thermo Fischer Scientific). When correlating IgE against single allergen components, we observed a significant positive correlation (n = 49; P < .001) between serum and nasal tests (Figure 1, A), with a median of all Spearman correlation coefficients (rs) across the whole panel of 0.77 (IQR 0.75, 0.85). The highest correlation coefficient was observed for Der p 2 and Aln g 1 (rs = .88), followed by Cor a 1 (rs = .87) and Bet v 1 (rs = .85) (Figure 1, B). We next determined the global sensitization profile of each subject's serum and nasal fluid and compared the profiles for all subjects (Figure 1, C). We observed a strong positive correlation between serum and nasal sIgE profiles, and the median Spearman correlation coefficient was rs = .75, the IQR 0.68, 0.88. The only poor correlations observed were for subjects No 01, 08, 16, 26, and 46. The highest correlations were observed for subjects with several sensitizations, whereas nonsensitized subjects showed poorer correlations (see Figure 1, D for overview over selected subjects). Finally, we evaluated the performance of the ISAC tests in serum and nasal fluid in comparison with the ImmunoCAP method by assessing cutoff, sensitivity, specificity, likelihood ratios, and operating characteristics. First, a nasal fluid cutoff threshold was estimated by a receiver operating characteristics (ROC) curve using Youden's index. The area under the curve (AUC) for nasal fluid (0.93) and serum tests (0.97) was found to be comparable (Figure 2, A). The nasal threshold was calculated to be 0.08 ISU-E. The diagnostic capability of sIgE determination for birch pollen (Bet v 1, Bet v 2, and Bet v 4), grass pollen (Cyn d 1, Phl p 1, Phl p 2, Phl p 5, and Phl p 6), and HDM (Der f 1, Der f 2, Der p 1, and Der p 2) was assessed by a two-by-two table (Figure 2, B). Specificity (serum: 0.95 and, nasal: 0.96) and positive prediction value (serum: 0.96 and nasal: 0.97) were similar for both methods. The diagnostic sensitivity and negative prediction value of serum diagnostic were higher than nasal diagnostic (TPR serum: 0.94 vs TPR nasal: 0.85; NPV serum: 0.92 vs NPV nasal: 0.82). In addition, diagnostic accuracy was determined by calculating likelihood ratios for serum (LR+ 17.83, LR− 0.07) and nasal biosampling (LR+ 24.28, LR− 0.15). Further statistical analyses were done to complement the results (Figure 2, C). We demonstrate similar specificities of ISAC for serum and nasal fluid tests, whereas the sensitivity in the serum test is higher than in the nasal test. A likely explanation for the lower sensitivity in our nasal tests is that the manufacturer's instructions are optimized for the serum matrix. Consequently, the experimental setup (eg, incubation times, fluorescent marker, sampling methods) should be improved further to raise sensitivity of nasal fluid diagnostic. Moreover, the threshold for the nasal fluid test, as assessed in the current study, could be set to an even lower value (0.08) than recommended for serum by the manufacturer (0.3) without losing specificity. Overall, sIgE levels against all tested allergen components were significantly and positively correlated between nasal fluid and serum, and the inter-sample correlation was best for sIgE against birch and grass pollen and HDM (Figure S2. online supporting information). Recent studies comparing ISAC tests in serum and nasal fluid have shown similar results6-9; however, these studies compared only tests for single allergens, that is, house dust mite, Japanese cedar, mugwort pollen, and fungal spores, instead of a whole aeroallergen panel. To conclude, we present the first study to assess whole patterns of IgE specific to aeroallergens in serum and nasal fluid and to systematically evaluate the novel, ISAC-based method in comparison with clinical standard diagnostics. Our results could be of high relevance for the future improvement of clinical diagnostics, especially in children with allergic airway disease. The authors declare no conflicting interests. Impuls- und Vernetzungsfonds (IVF), Helmholtz Gemeinschaft; EU-COST Action DiMoPEx (Grant Number CA15129). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. 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