The mainstay of respiratory allergy diagnosis is skin prick testing and blood RAST testing for specific IgE to various inhalant allergens including dust mites, pets, pollens and mould spores. Many patients with typical nasal allergy symptoms of nasal itching, congestion, sneezing, profuse mucus production and eye irritation may blood test negative for allergy to common inhalant allergens with no specific IGE and negative skin prick tests. One would then diagnosed this as Non-allergic rhinitis and labelled these patients as having no allergies. However many do still have allergy related Eosinophil cells in their nasal mucus (called Non-allergic rhinitis with eosinophilia syndrome or NARES).
It is now well recognised that 40% of these NARES patients do still produce localised specific IgE in their nasal mucus to common inhalant allergens. This localised IgE produced remains in the nasal mucus and membranes and does not enter the systemic blood steam, so conventional allergy tests on blood and skin remain negative. They do however respond to allergy controlling antihistamines and steroid nasal sprays and may respond to desensitization immunotherapy to the offending allergens.
It should be possible to measure this specific IgE on a sample of nasal mucus, but at present this test is not yet commercially available.
Reference: Rondon C, Canto G, Blanca M. Local allergic rhinitis: A new entity, characterization and further studies. Curr Opin Allergy Clin Immunology 2010: 10 (1); 1-7
