Your allergist may recommend allergy tests, such as a skin test or blood test to determine if you have a food allergy. In an allergy skin test for a food, a very small drop of a liquid food extract, one for each food needing to be tested, is placed on the skin. The skin is then lightly pricked. This is safe and generally not painful. Within 15 to 20 minutes, a raised bump with redness around it, similar to a mosquito bite, may appear. This test shows that you are sensitized to the food and probably allergic to that food. A sensitivity to a food can be indicated in a skin prick test or a blood test, but does not always show a true allergy unless there has been a previous reaction to the food.
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Sometimes, an allergy blood test may be used. This typically involves drawing blood from a vein in the arm and the results are not usually available for at least one week.
If done correctly and interpreted by a board-certified allergist, skin tests or blood tests are reliable and can rule in or out food allergy. Some people test "allergic" to a food (by skin or blood testing) and yet have no symptoms when they eat that food. To confirm test results, your allergist may recommend an oral food challenge. This means that you eat or drink small portions of a food in increasing amounts over time to see if an allergic reaction occurs. This is usually done under a physician’s supervision in a doctor’s office or hospital setting.