Principles of Allergy Diagnostics

Adequately mastering the principal diagnostic tests available in pediatric allergy is fundamental for correctly managing the patient. This chapter introduces the main tools available to physicians for the diagnosis of allergic diseases, in particular, in vivo and in vitro tests will be discussed, such as skin tests, intradermal tests, serum total immunoglobulin E (IgE) dosage, serum allergen-specific immunoglobulin E (sIgE) for allergens and allergen components dosage, basophil activation test (BAT), fraction exhaled nitric oxide (FeNO), blood count with eosinophil count, eosinophil count in induced sputum, and allergen provocation test. Furthermore, each method’s relative indications, advantages, and disadvantages are analyzed. Currently, the skin prick test (SPT) remains the first level of investigation in most cases; the serum dosage of IgE against allergenic extracts or components allows us to define more precise diagnoses through molecular allergy diagnostics. The BAT is a relatively new method that has to be validated internationally. In some cases, such as for food and drug allergies, challenge tests still represent the gold standard for diagnosis; in others, they play an almost marginal role and are relegated to particular situations.