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Wise et al.

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sensitivity if the patient was less than 30 years of age. 792 For the group older than age 50 years, ImmunoCAP was more sensitive. 792 Intradermal or epicutaneous testing demonstrates higher sensitivity but lower specificity than SPT for several allergens. 793,856,931,932,944 Based on this, intradermal tests should be selected judiciously. There is evidence to suggest that a positive intradermal reaction to grass pollen in the setting of negative prick testing may not be clinically relevant. 793,856 In recent years, microarray allergy testing systems such as ImmunoCAP ISAC (Thermo Fisher Scientific/Phadia AB, Uppsala, Sweden) have been introduced in an effort to offer a comprehensive in vitro allergen test panel. 794 The precision and utility of microarray testing needs more rigorous scrutiny so that consensus guidelines can be more firmly established. 794,945 The cost of a single Immuno-CAP ISAC test, which includes 112 components from 51 allergens, is approximately $500 to $600 in the United States. 794,945 Various studies have compared sIgE serology to allergen SPT. 793,943,946,947 Both techniques are sensitive and are generally well correlated; however, interpretation of the results depends upon the gold standard reference used to define allergic status. Environmental chambers, nasal challenge, and validated questionnaires are typically used to determine the diagnostic accuracy of allergen testing. Table VIII.F.3-2 summarizes several comparative studies between skin testing for aeroallergens, specific IgE serology, and other in vitro tests. It is important to understand that selection and interpretation of allergen testing is not based on sensitivity and specificity alone. The intended physiological mechanism to be interrogated also needs to be considered. SPT and intradermal testing both measure end organ pathological mechanisms associated with sIgE bound to the surface of mast cells. In contrast, serum sIgE testing and microarray approaches measure circulating IgE that may or may not represent downstream allergic inflammatory responses. Both intradermal testing and SPT rely heavily on technician skill for interpretation of the wheal and flare reaction. 856,928,937 In the case of subjects with dermatographism (or other inflammatory skin conditions in the testing area), hairy arms, or darkly pigmented skin color, the interpretation of the SPT can prove to be difficult. 942 Specialized imaging systems have been developed to measure the wheal reaction in an automated fashion in both light and dark skinned individuals, but additional validation is required. Until these automated systems become more widespread, in vitro testing affords the benefits of temporal and multicenter reproducibility. The average pooled sensitivity of SPT is 85% which is often slightly higher than that of serum sIgE testing 830 ; however, this is not universally true depending on the allergen tested and the characteristics of the patient. Based on accuracy, convenience, cost, and promptness of results, SPT is often chosen as the first line diagnostic instrument to detect sensitivity to aeroallergens. Intradermal testing can be used as a second line test to exclude reactivity if the clinical suspicion is very high. In cases where dermatographism is present and/or patients are unable to wean off medications that affect skin testing, sIgE testing may be a better choice. More studies are required to determine the role of small volume blood testing through emerging microarray technology such as the ImmunoCAP ISAC.

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Int Forum Allergy Rhinol . Author manuscript; available in PMC 2020 June 10.