international human serum IgE reference preparation and are quantitatively pre­sented within the range of 0.10–100kU/L.Also results are reported by classes (0– VI) (Table17.3). The positive sIgE is considered conventionally as >0.35kU/L.For certain foods, 95% cutoff values of sIgE have been established using the ImmunoCap System to predict clinical reactivity, in children with food allergies. However, there are no established sIgE cutoff thresholds available for predicting clinical reactivity to aeroallergens. Patients with high sIgE levels are more likely to exhibit symptoms upon allergen exposure compared to those with lower sIgE levels. Nonetheless, it’s crucial to note that high sIgE levels do not necessarily indicate the severity or inten­sity of the allergic reaction. The precise threshold quantities of allergens that may trigger clinical responses in patients have yet to be rmly established. Nevertheless ≥Class 3 levels provide facilitate to clinicians determining the culprit allergen, if consistent clinical history is available. Since <3 Class levels may be attributed to sensitivity in some individuals, who have no clinical ndings. The sensitivity and specicity of immunoassays are inuenced by the technology used and the quality of allergens employed. Generally, these assays exhibit a specicity and sensitivity range of 30–95% and 60–95%, respectively [12, 35]. The reported sensitivity of these immunoassays is approximately 75% when compared to prick/puncture skin testing [12]. One limitation of sIgE assessments is their tendency to detect varying sIgE positivity in individuals without accompanying clinical symptoms, particu­larly among patients with very high IgE levels. Currently, no established threshold of total IgE exists to determine false positivity in these cases. One of the benets of using sIgE tests is that they are not inuenced by the use of antihistamines, dermog­raphism, or skin problems. Additionally, these assays may be conducted in individu­als who are at a high risk of anaphylaxis due to SPT.The comparison of the SPT and sIgE assays is shown in Table17.4 [36, 37]. While both SPT and sIgE testing are available, employing both in clinical practice might not always be necessary. The choice of diagnostic testing should be made on an individual basis to prevent unnec­essary costs. These testing procedures should be reserved for situations where iden­tifying additional allergic sensitizations would signicantly inuence the patient’s treatment and overall well-being [38].

The ability to diagnose allergy disorders has signicantly improved with the molecu­lar analysis or CRD through development of microarray technology. CRD involves identifying specic IgE against puried native and recombinant allergenic com­pounds. CRD provides a detailed representation of the sensitization pattern in patients with multiple sensitivities, assists in identifying cross-reactivity and co-sen­sitization, and contributes to the rule-out allergy [39]. Allergens are classied into two subtypes: major allergens and minor allergens. A major allergen is dened as an allergen recognized by more than 50% of the sensitized population. Major allergens are primary triggers for the production of specic IgE and subsequently induce aller­gic reactions. Allergic reactions to minor allergens are frequent in regions with sig­nicant exposure to these allergens. Understanding a patient’s sensitivities to both major and minor allergen components becomes crucial, especially in the context of considering immunotherapy. This is due to the fact that commercial extracts are typi­cally well standardized only for major allergens. In the case of pollen allergy, CRD plays a pivotal role in identifying genuine allergenic molecules, aiding in the deci­sion-making process for immunotherapy. A study from the European Community Respiratory Health Survey revealed that nearly a quarter of the patients were poly­sensitized with pollens, this has signicant implication on deciding to prescribe immunotherapy [40]. Storage proteins, oleosins, defensins, nonspecic lipid trans­port proteins (nsLTP), PR-10 proteins, prolins, and cross-reactive carbohydrate determinants (CCD) are signicant protein families to give rise allergy [41]. Cross­reactivity can occur when two molecules from different species share more than 70% similarity in their primary amino acid sequence. There are known cross-reactivities among pollen–pollen, plant food–plant food, pollen–plant food, and pollen–plant food latex [42]. Due to their similarity to the genuine molecule, cross-reactive aller­genic molecules can only trigger an allergic reaction after prior interaction with the primary sensitizer [41]. Type 1 food allergens induce allergic reactions after being absorbed from gastrointestinal tract however type 2 allergens elicit allergic reactions

once patient is being sensitized to inhalant allergens. When people with a pollen allergy especially with birch pollen (Bet v 1) consume fruits and vegetables, they may experience the Pollen Food Allergy Syndrome (PFAS). This syndrome triggers an acute and generally mild allergic response in the oral mucosa. Cross-reactivity between pollen allergens and fruit and/or vegetable allergens results in the formation of PFAS, which is associated with plant-related allergy components present in fruits and vegetables such as lipid transfer proteins, prolin, and PR-10 proteins [43]. In a small subset of patients with allergic rhinitis triggered by grass pollen allergy, sensi­tization to prolins, which are pan-allergens found in fruits, may occur. Prolins, along with Cross-Reactive Carbohydrate Determinants (CCD), exhibit high cross­reactivity with pollens, yet their clinical signicance appears limited. Moreover, their quantication in Allergen Immunotherapy (AIT) extracts is generally not performed. Polysensitization to animal dander from cats, dogs, and horses is well-known and might be explained by cross-reactive lipocalins and albumins, detectable through CRD.CRD holds promise in predicting the risk of systemic reactions in food aller­gies among specic patients due to certain allergen components associated with severe allergic reactions. In the instance of peanuts, Ara h 2 (a storage protein) appears to be the best predictor of peanut allergy, decreasing the need for peanut challenges by at least 50%. Similarly, in hazelnut allergies, Cor a 9 and Cor A 14, and in soybean allergies, Gly m 5 and Gly m 6, have been identied as components linked to severe allergic reactions [44]. CRD emerges as a valuable tool in cases of anaphylaxis where the cause cannot be identied through medical history alone. However, when diagnostic tests, including SPT and sIgE, are inconclusive, the CRD can be utilized since it identies more allergens than SPT and sIgE.Therefore CRD could be highly helpful in cases of anaphylaxis caused by hidden allergies [45]. Studies have shown that among patients experiencing idiopathic anaphylaxis, nearly half were found to have new allergenic sensitizations, with approximately 20% of these cases identifying the probable cause of the anaphylaxis [46]. Singleplex and multiplex assays are used in CRD.Singleplex tests assay the allergen selected based on the patient’s medical history, clinical data, and skin prick test results. On the other hand, multiplex-microarray assays detect multiple specic IgEs against various aller­gens simultaneously. A multiplex CRD should generally be carried out for complex instances with multiple sensitizations to food and respiratory allergens as well as for idiopathic anaphylaxis. CRD exhibits a sensitivity ranging from 66 to 100% for food allergens, while its specicity varies from 0 to 95%. These results have been derived from studies utilizing food challenge tests as a gold standard method. However, there is no established gold standard method used to ascertain the sensitivity and specic­ity of CRD for inhalant allergens. Nevertheless, CRD results can be compared either with SPT outcomes or with specic IgE determination methods using allergenic extracts.

Tryptase is main biomarker of mast cells, which takes play a role in Type 1 hyper­sensitivity reactions. Strong activation signals, such as the cross-linking of FceRIgE