At a glance
Also known as
RAST test; allergy screen; IgE
Why get tested?
To screen for allergies, to identify particular
When to get tested?
When you have such as a rash, , rhinitis (nasal congestion), red itchy eyes or asthma that your doctor suspects may be caused by an allergy
A blood sample drawn from a vein in your arm.
Test preparation needed?
What is being tested?
is a associated with allergic reactions that is normally found in very small amounts in the blood. IgE functions as part of the body's (its defence against 'intruders').
When someone with a genetic predisposition to allergies is exposed to a potential 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 that binds to specialised cells in the tissues (called 'mast cells'), and a type of white blood cell, known as a , 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.
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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
What other tests are available for allergy testing?
Skin prick, patch tests and oral food challenges are usually done by an immunologist, allergist or dermatologist. Your doctor may also try eliminating foods from your diet and then reintroducing 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 is possible.
My allergy test was negative, but I am having symptoms. What else could it be?
You could have a hypersensitivity such as Coeliac disease
(sensitivity to gluten in the diet), or an enzyme deficiency, for example, lactase deficiency which causes lactose intolerance. Alternatively, you may have an allergy-like condition that is not mediated by IgE for which there are no specific laboratory tests. It is important to investigate your individual situation with your doctor’s assistance.
My allergy symptoms are generally mild. How serious is this really?
Allergic reactions are very individual. They can be mild or severe, vary from exposure to exposure, get worse over time (or may not), involve the whole body, and can sometimes be fatal.
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 medications such as antihistamines and portable adrenaline injections, is the safest course. Immunotherapy can help decrease symptoms for some unavoidable allergies, but is not yet commercially available for food allergies and the treatment is very time consuming usually consisting of years of regular injections.
Why am I told to avoid fresh fruit when my allergy is to tree pollen?
There are cross-reactions between some airborne allergens and fruit proteins. Your body thinks it is detecting tree pollen and creates an allergic reaction to the fruit because the antibody it makes against tree pollen will recognise fruit proteins present in apples, pears, peaches and some other fresh fruit. This however, is a relatively less common occurrence in Australia as opposed to Europe and the USA.