Should you test your child for allergies?

The factors and causes of allergies — and what to expect when you visit the doctor.

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No age is too young to test for allergies, says Janet Roberts, a paediatric allergist and president of the Canadian Paediatric Society’s Allergy Section. “You can be tested as soon as you notice a problem that requires evaluation.” But a child needs to be exposed to a potential allergen before becoming allergic. For example, he’s not likely to have pollen allergies until he’s lived through a few spring seasons.

At the first visit, the allergist will take a history and do a physical exam. Maybe your baby developed a rash after drinking formula, or your school-ager gets puffy eyes when playing with the family pooch. It’s important to share that info. “You start with the problem. You don’t start with tests,” says Roberts. And other causes need to be considered first — what you may think is a reaction might be a cold or food poisoning. Kids with persistent asthma, frequent ear infections and eczema are more likely to have allergies. But contrary to popular belief, kids with a family history of allergies aren’t necessarily more likely to develop the same allergies as their parents or siblings. Certain things like dairy and nut allergies do run in families, but it doesn’t up the odds by much. For instance, peanut allergies affect one to two percent of all children; the risk only rises to five percent if an older sibling already suffers. Plus, if your younger child is growing up in a nut-free home because her brother has a peanut allergy, she may not have had the exposure to become allergic.

But there are no practical-to-administer tests (outside of a research setting) that will give you an absolutely definitive answer. Rather, the information helps the doctor figure out how likely your child is to have a reaction to a given substance. “Nothing is 100 percent,” says Roberts. “False positive and false negatives tests are possible. The allergist will interpret the results in the context of the child’s problem.”

What’s an intolerance?
It can be tough to tell the difference between a food allergy and an intolerance, because some symptoms are the same, including diarrhea and vomiting. Intolerances are usually caused by an enzymatic deficiency which results in the inability to digest or absorb certain foods; other symptoms include bloating and gas. In contrast, food allergies may manifest as hives, swelling or difficulty breathing.

A version of this article appeared in our April 2012 issue, with the headline Put Allergies to the Test (p. 38). To see more on this subject visit our allergies section.

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