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Allergy Testing

Allergy Testing

Allergy testing in younger children is often a controversial subject. Parents often want their children tested for suspected allergies, but doctors usually want to try and eliminate common things that trigger allergies, try allergy medicines or they just say your child is too young for allergy testing. Should every child with allergies have testing? Probably not. The main reason to do allergy testing is either to figure out what a child is allergic to so that you can eliminate his exposure to it or if you are interested in starting allergy shots.

If you are just trying to figure out what your child is allergic to, then it is reasonable to try and restrict his exposure to the most common things that trigger allergies (also called allergens). These include dust mites, mold and animal dander. Common foods that cause allergies include milk, eggs, peanuts, soy, wheat, fish, shellfish and tree nuts.

Other common allergens include pollens, grasses, weeds, trees, medications and insect venom from a bite or sting. These types of allergies are easier to detect, since allergies to plants, etc. should be seasonal, and reactions to medications or insect bites will only occur after these specific triggers.

The problem with eliminating these common triggers is that it can be very hard and tricky to do it completely. Foods often have 'hidden ingredients' that you may be unaware of. Did you know that if your child is allergic to milk, then he should avoid foods with casein, lactalbumin, nougat, and whey? Plus restricting too many things in your child's diet makes it harder to give him an adequate amount of calories, vitamins and minerals to stay healthy.

Or he may be exposed outside the home. For example, if he is allergic to cats, even if you get rid of your own cat, if someone in his school or daycare has a cat at their own home, then the cat dander on this child may be enough to trigger your child's allergy symptoms. And the dander may stay in your own house for several months, even after you get rid of the animal.

How aggressive you are in finding what your child is allergic to also depends a great deal on how severe his symptoms are. If he simply has a runny nose, rash or diarrhea, then it is not as important to quickly find what he is allergic to. However, if he had a life threatening anaphylactic reaction, then finding what he is allergic to would be more of a priority.

Also keep in mind that not all reactions, especially to foods, are true allergic or immune reactions. For example, a child with lactose intolerance will have normal allergy tests. And if they are immune system reactions, not all of them are mediated by IgE, which is what allergy tests look for. Some non-IgE mediated immune reactions to foods include those that can cause eczema to flare, Celiac disease and food protein induced syndromes, which commonly occur in infants allergic to milk or soy proteins.

A careful history of your child's symptoms can help to determine if even has allergies.


  • What symptoms does he have?
  • When do they occur?
  • Do they happen right after he is exposed to something or eats a certain food? Most food allergies cause symptoms within minutes to a few hours.
  • Do the symptoms occur every time that he is exposed to something?
  • What are the results of your elimination diet, where you eliminate a certain food for up to a week at a time to see if your child's allergy symptoms disappear, and food diary, where you record your child's diet and any symptoms he may have within a few hours of eating them?
The prick skin test is the most commonly used test to detect allergies. Although not always accurate in children under the age of 12 months, it can be done at any age. According to the American Academy of Pediatrics, 'age is no barrier to skin testing; positive results can be obtained at any age.' Skin testing is done by placing drops of common allergens on your child's skin. Light pricks or scratches are then made in the skin and the area is observed for a reaction. The test is relatively painless and very quick. To avoid false results, your child will have to stop taking antihistamines if he is currently taking them as treatment for his allergies.

Another type of allergy test is the intradermal skin test. This is similar to the prick skin test, except that the allergen is injected under the skin. It is more accurate, but may not be as well tolerated as the prick skin test in younger children.

Other tests include RAST (radioallergosorbent test, a blood test to check for antibodies against certain things your child may be allergic to) to see if specific allergies can be found. A new version of the test, the ImmunoCAP allergy blood test, is supposedly much improved over older versions, although skin testing is usually thought to be more accurate. The main downsides to RAST testing is that it is more expensive than skin testing, and the results can take up to a few weeks to come back, while the results of skin tests are usually known within 15 minutes of the test being performed.

Other, nonspecific tests, such as total serum IgE and blood eosinophil levels, are not very helpful, as they give no information about what you may be allergic to.

So if it is possible to do allergy testing in children, why don't you just do it on all children with allergies? One reason is that just because you have a positive test, which indicates that you do have IgE against a certain allergen, that doesn't mean that it will cause any symptoms. According to the American Academy of Pediatrics, 'Although a positive result to scratch or intradermal skin testing strongly suggests that your child has formed IgE antibodies against a specific allergen, it does not follow that he will develop allergy symptoms when exposed to that particular allergen in the environment.' And skin test results can remain positive, even as your child is outgrowing his allergies.

Also, allergy tests can not detect every possible allergen. So your child may still be allergic to something, even though all of his tests are normal.

So the results of your child's skin tests must be interpreted in light of his symptoms and history and are best done by allergy expert. Although allergy tests, especially RAST, are easy to order, and are often done by doctors without formal training in diagnosing and treating allergies, they are often hard to interpret.

Your doctor may also do a food challenge, where small amounts of a food is given to your child and he is closely observed for symptoms.

Other allergy tests are very controversial and best avoided, including the cytotoxic leukocyte test, sublingual drops test, and immune complex assays.

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