Laboratory Tests in Pediatric Allergy

In vitro tests are part of the diagnostic pathway of allergic diseases. Circulating eosinophils are a marker of type 2 inflammation. Mild and transient eosinophilia can be due to atopic diseases, asthma, drug hypersensitivity, helminthic infections, or be idiopathic; instead, hypereosinophilia (moderate to severe and persistent or marked tissue eosinophilia) should be promptly investigated. The eosinophil cationic protein, evaluable in various biological fluids, is an index of eosinophil activity that can be increased in atopic and non-atopic conditions. Total serum IgE are a marker of atopy, influenced by many factors and increased also in non-allergic conditions, and should always be evaluated when specific IgE are tested. The latter are a marker of sensitization to a specific allergen that can be dosed individually or with multi-allergen tests. The basophil activation test is a functional assay that evaluates IgE function through the activation of basophils by a specific allergen. Nasal cytology is a simple tool that helps to characterize rhinitis, distinguishing allergic rhinitis from non-allergic rhinitis.