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First, keep in mind that allergy tests are not the sole basis for diagnosing or treating an allergy. Health care providers make an allergy diagnosis based on several factors:
- History of the child's experiences and family history of allergy/asthma
- Physical exam of the child to detect signs of allergy
- Allergy testing for sensitivity to specific allergens
Allergy tests help your physician confirm allergies your child may have. When an allergy test pinpoints a reaction to a specific allergen(s), your health care provider also can use this information in developing "immunotherapy" - allergy shots - specifically for your child, if appropriate.
Skin Tests for Allergies
Skin prick tests are the most common tests for allergy. Small amounts of suspect allergy triggers are introduced through the skin of the arm or back by pricking or puncturing the skin with a needle or similar device. If your child is allergic to a substance, you will see a raised, red itchy bump, also called a "wheal." Reactions usually appear within 15 minutes. This positive result indicates that the IgE antibody is present when your child comes in contact with the specific allergen. The size of the wheal is important: the bigger it is, the more sensitive your child is to that particular substance. This test is the least time consuming and expensive. You may have to discontinue certain medications, especially antihistamines, several days prior to testing.
There are four kinds of skin tests: scratch, puncture, prick and intradermal. Your allergist may use one or more skin tests to analyze your child's response to various substances. Keep in mind that you may see a false-positive or a false-negative
skin test. Results often depend on how well the test is performed.
Skin prick, puncture and intradermal tests may be difficult with young children afraid of needles. There is some possibility of a life-threatening anaphylactic response if a person is extremely sensitive to a substance. Your health care provider will be prepared to react swiftly to this kind of response.
Blood Tests for Allergies
The RAST (radioallergosorbent test) and related blood tests use radioactive or enzyme markers to detect levels of IgE antibodies. These tests are useful when a skin test is difficult due to a widespread skin rash, anxiety about skin pricks, or if the child has the potential for a sudden and severe allergic response to test allergens.
Skin tests and these blood tests are very comparable in their ability to diagnose sensitivity to specific allergens. Both kinds of tests are considered to be about 90 percent accurate.
Elimination Diet
An elimination diet is often used to help isolate sensitivity to specific foods. Your health care provider sets up a diet without foods that you suspect may affect your child. Because milk, soybeans, eggs, wheat, peanuts, nuts, shellfish and corn are the main culprits for more than 80 percent of people who have food allergies, these foods are usually not included in the starting diet.
Your child will stay on the prescribed diet for four to seven days. If the symptoms do not subside, additional foods are eliminated until the allergy symptoms stop. Once the symptoms disappear, new foods are added to the basic diet, one at a time, until symptoms reappear.
The chief drawback to an elimination diet is making sure your child is eating "pure" foods. Common food allergens are "hidden ingredients" in hundreds of packaged or processed foods. In order for an elimination diet to be successful, check ingredients for foods you give your child to eat. If your child is a fussy or picky eater, an elimination diet can be difficult. Your health care provider can suggest helpful approaches.
Fasting is a radical way to identify food allergies. Although very effective for detecting problem foods, this kind of elimination diet is hard to do with children. Fasting is best done under medical supervision and often is used for "extreme" cases where a child is suspected to have allergies to many types of food.
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