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Immunoglobulin E (IgE) is a protein associated with allergic reactions that is normally found in very small amounts in the blood. IgE functions as part of the body's immune system (its defence against 'intruders').

When someone with a genetic predisposition to allergies is exposed to a potential allergen such as grass pollen or cat fur for the first time, they may become sensitised. Their body sees the allergen as a threat and creates a specific IgE antibody that binds to specialised cells in the tissues (called 'mast cells'), and a type of white blood cell, known as a basophil, in the blood stream. Mast cells are found throughout the body but are highest in the skin, respiratory system and gastrointestinal tract.

If the person is exposed to the allergen again, these attached IgE antibodies recognise the allergen and cause the mast cells and basophils to release histamine and other chemicals, resulting in an allergic reaction that begins at the exposure site.

The allergen-specific IgE antibody test is used to screen for an allergy to a specific allergen. It measures the amount of that suspected IgE antibody in the blood. The specific IgE tests can be for one particular allergen or a group of them and it can be very specific, for example subcomponents of peanut such as Ara h2. Groupings of these tests, such as food panels or regional weed, grass and mould panels, can be done. Alternatively, you and your doctor may pick and choose selectively from a long list of individual allergens suspected of causing your allergies. white color prom selections with lace

The allergen-specific IgE test can be done using a variety of methods. The method that has been used and studied for the longest time is the RAST (RadioAllergoSorbent Test), this is not a method currently in use but an allergy test is often wrongly referred to as a RAST test.