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Immunology Laboratory

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Allergy testing

Allergy arises as the result of allergic inflammation where the patient's immune system interacts with the environment in such a way to cause the release of histamine and other proinflammatory mediators

The diagnosis of allergic disease is mostly made on clinical grounds supported by a detailed history and the outcome of skin tests, however laboratory investigations are a useful tool in the diagnosis and management of allergic diseases and can be very helpful in the assessment of disease activity.

The immunology laboratory provides a high quality diagnostic allergy service spanning simple to complex allergic reactions, including drug allergies, bee and wasp venom, food and animal allergens, House dust mites and other insect allergens, grasses and pollens, and numerous miscellaneous allergens. We also perform assays to help contribute to a possible diagnosis of anaphylaxis.

The assays performed by the clinical diagnostic laboratory play two critical roles in contributing to the diagnosis of allergic diseases

  1. Identify the allergens to which the patient has become sensitized is situations where Skin testing is unavailable or unsuitable; i.e in the presence of dermatographism or dermatitis, in pregnancy or in cases of suspected extreme sensitization where skin tests may be potentially dangerous. [Specific IgE assays]
  2. Detect and quantify the mediators of anaphylaxis that are released as a result of mast cell degranulation. [Mast cell tryptase measurement]

General notes on allergy testing

It is important to be specific when requesting specific IgE tests. If you are not sure whether we are able to test for IgE levels to a specific allergen, please contact the laboratory and discuss your requirements. The laboratory will not screen sera against a large panel of allergens in cases of questionable clinical hypersensitivity. Specific IgE testing is of no value in the absence of a full clinical history.

Please note that total IgE levels are of limited clinical value and are rarely essential. Normal levels do not exclude allergy. Very high levels of lgE are seen both in atopic eczema and in parasitic infestations and also in the rare hyper-IgE syndrome and extremely rare cases of IgE myeloma.

IgE will be measured to differentiate IgE - from non IgE-mediated disorders, where this is difficult by clinical means, to identify patients at risk of allergic disease, whether or not they are symptomatic. This particularly applies to early childhood.

NICE guidelines for allergy testing (CG116)

Results interpretation

The relevance of allergen specific IgE must be carefully assessed in the context of the clinical history. Normal IgE level makes atopy unlikely, however, it does not exclude sensitisation to individual allergens. As a general rule even weakly positive allergen specific IgE may be clinically relevant in patients with a low normal IgE.