To test for suspected allergies.
Allergy Testing
When you have symptoms such as hives, dermatitis, rhinitis (nasal blockage, sneezing), red itchy eyes, asthma, or severe reactions such as anaphylaxis that your doctor suspects may be caused by an allergy
A blood sample taken from a vein in your arm
None
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How is it used?
The allergen-specific IgE antibody test is done to test for an allergy (a type I hypersensitivity) to a specific substance or substances when a patient presents with acute or chronic allergy-like symptoms.
The allergen-specific IgE antibody test may be done when skin prick tests are not possible. If the patient has significant dermatitis or eczema or is taking anti-histamines, skin prick tests are difficult to perform and/or interpret.
The allergen-specific IgE antibody test has limited use in checking whether a patient has outgrown an allergy as the test may remain positive even in someone who has long outgrown their allergy. The usefulness of allergen-specific IgE to monitor response to immunotherapy is unclear, and may remain positive even after successful immunotherapy.
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When is it requested?
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What does the test result mean?
Normal (negative) results indicate that you probably do not have a "true allergy", an IgE-mediated response to that specific allergen, but the results of allergen-specific IgE antibody tests must always be interpreted and used with caution and with the advice of your doctor. No test is perfect and, though a negative test means allergy to that substance is unlikely, it does not completely exclude allergy.
Elevated results often indicate an allergy. However, not all patients with a positive specific IgE test will have an actual physical allergic reaction when exposed to that substance – the patient in this case is said to be “sensitised” rather than allergic to the substance. The amount of specific IgE present does not necessarily predict the severity of a reaction, although the higher the level the more likely the patient is to have a reaction of some sort to the allergen. Your clinical history and other allergy tests, done under close medical supervision, may be necessary to confirm an allergy diagnosis.
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Is there anything else I should know?
Sometimes your doctor will look at other blood tests for an indirect indication of an ongoing allergic process, including your total IgE level or your full blood count (FBC) and white blood cell differential (particularly eosinophils). Elevations in these tests may suggest an allergy, but they may also be elevated for other reasons.
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What other tests are available for allergy testing?
Skin prick or intradermal tests, and oral food or drug challenges are usually done by an allergist or immunologist. Your doctor may also try eliminating foods from your diet and may reintroduce them to find out what you are allergic to. It is important that these tests be done under close medical supervision, as a life threatening anaphylactic reaction, though rare, is possible.
Patch tests are used in the investigation of 'allergic contact dermatitis', and check for delayed reactions to substances which are in contact with the skin, eg fragrance in cosmetics, nickel. These tests are may be performed by immunologists, allergists and dermatologists. These reactions do not depend on IgE and so the IgE test may be normal. However, these generally have very different signs and symptoms to IgE related disease. A carful assessment of your symptoms will enable your doctor to choose the appropriate tests for you.
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My allergy test was negative, but I am having symptoms. What else could it be?
You could have an allergy-like condition or intolerance that is not caused by IgE for which there are no specific laboratory tests. Or it could be another disease that is causing allergy-like symptoms. It is important to investigate your individual situation with your doctor's assistance. In the case of bowel symptoms after food, there can be other causes such as coeliac disease, an autoimmune reaction to gluten, or lactose intolerance, caused by a common enzyme deficiency.
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My allergy symptoms are generally mild. How serious is this really?
The severity of an allergic reaction varies greatly from one person to another. They can be mild or severe, vary from exposure to exposure, get better or worse or not change over time. They may be local or involve the whole body. Although most people cope with their allergy, fatalities do rarely occur, mainly in patients with severe food allergy.
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Will my allergies ever go away?
Although children do outgrow some allergies, adults usually do not. Allergies that cause the worst reactions, such as anaphylaxis caused by peanuts, do not usually go away. Avoidance of the allergen and advance preparation for accidental exposure, in the form of drugs such as antihistamines and portable adrenaline injections, is the safest course. Immunotherapy can help decrease symptoms for some unavoidable aeroallergens such as pollens, and this treatment usually consists of years of regular injections. This approach is not advocated for food allergens.
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Why am I told to avoid fresh fruit when my allergy is to tree pollen?
This is due to “oral allergy syndrome”. There are substances in tree pollen that are very similar to those in certain fresh fruits. If your immune system makes IgE to these substances in pollen, this IgE may also “crossreact” with the fruit proteins. Your body thinks it is detecting and reacting to tree pollen when in fact it is fruit that it is responding to. Oral allergy syndrome is quite becoming more common, though in most cases it is mild, with tingling or a scratch sensation in the mouth or throat.