This is the most common test used to pinpoint allergies. You can be tested for up to 25 allergens at any one time. Small amounts of the suspected allergen are pricked into the skin of the back or forearm with a tiny prong about 1 mm long. You will not be injected with anything and it will not hurt. If you are allergic to a substance you will develop a weal, a small bump that may be itchy and red around the perimeter.
The doctor will measure the weal after about 15 minutes and anything bigger than 3 mm will be regarded as a positive result. This test is a good indication of the substance to which you may be allergic, but it is not foolproof. Some allergens, such as pollen, dust and fungi perform better than foods, which are unreliable. Similar tests include the intra dermal infection test, which produces a weal and is not common, and the patch test, where the suspect substance is placed on a small patch of lint and stuck on the skin for between 48 and 72 hours.
RAST is a blood test that measures the number of a special allergy antibody your immune system has produced to a particular substance, such as pollen, the house dust mite or a food protein. A small amount of your blood is taken from a vein and sent to a laboratory for testing. Here a drop of your blood serum will be applied to a sample of the allergen.
The test uses a technique whereby a radio active marker attaches itself to the antibody cells and the total amount of radio activity is measured at the end of the test.
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