Seeking allergy when it hides: which are the best fitting tests?

Cristoforo Incorvaia, Nicola Fuiano, Giorgio W Canonica

In the common practice of respiratory allergy, the confirmation by IgE tests of the relationship between the occurrence and duration of symptoms and the exposure to specific inhalant allergens allows an aetiological diagnosis. However, to see patients with suggestive history but negative IgE tests is not rare, and this generally leads to a diagnosis of nonallergic rhinitis or asthma. In many cases, such diagnosis is wrong, because the patient may be revealed as allergic by using additional testing. This is true for local allergic rhinitis, characterized by an exclusive IgE production in the nasal mucosa, that may be correctly diagnosed by performing a nasal IgE measurement or a nasal provocation test with the suspected allergen (s). Another misleading issue is the role of T cell-mediated, delayed hypersensitivity in the pathophysiology of rhinitis and asthma. Recent studies showed that in patients with rhinitis or asthma and negative IgE tests, especially when there is a positive history for current or past atopic dermatitis, the clinical symptoms are actually driven by such mechanism, that may be detected by performing an atopy patch test (APT). The allergen source most frequently responsible for this kind of allergy is the house dust mite, but other allergens may also be involved. Thus, before delivering a diagnosis of nonallergic rhinitis or asthma in patients with negative result to common allergy testing, further tests are needed. To miss the diagnosis of allergy has obvious consequences in terms of management, including allergen avoidance, patient's education, and specific immunotherapy.