Tips on Testing
If you suspect your child has a food allergy, preparation and planning is key to diagnosis and management.
Keep a food diary. As with any baby, irrespective of allergies, introduce new foods one at a time, two to three days apart. Record everything that your baby eats for several weeks as well as any related symptoms (eczema, fussiness, gas).
Talk to your pediatrician and visit an allergist. Although it may be tempting, don't diagnose your child's allergy. Establish good relationships with doctors you trust who can advise you.
Get your child tested. Your doctor may recommend a radioallergosorbent test (RAST) or a prick-skin test. RAST, the latest version of which is ImmunoCAP, is a blood test that measures levels of antibodies to specific food proteins. High levels of antibodies indicate a possible allergy. It can take anywhere from a few days to a week to get results from this very sensitive test; 50 to 60 percent of positive RAST results are false positives. In prick-skin tests, results are nearly immediate: Any food that causes a raised bump or hive is positive. Fifty to 60 percent of positive skin test results are also false positives.
"Both of the tests measure the same things," explains Dr. Assa'ad. "It's not like one test is better than another," she adds. "Go into an allergist's office, you're going to get the skin test; go into a pediatrician's office, you're going to get the blood test."
If personal histories are uncertain and preliminary tests are inconclusive -- say your kid's prick-skin test registers a wheat allergy but her favorite snack is toast -- she may need the most accurate test available. A food challenge, which medical staff must closely monitor, requires that the patient ingest gradually increasing amounts of an allergen and wait for a reaction.
Learn more. Dr. Assa'ad, who tests babies as young as 3 months to see if they tend to be allergic, points out that any test is only valid for that individual at a particular point in time. A child who has eaten peanut butter and jelly for years, for example, could one day have an allergic reaction to her once-favorite meal. On the other hand, my sons, who used to have an extreme reaction to eggs, now enjoy baked goods and other foods containing cooked eggs. To get a good handle on the developing immune system, Dr. Assa'ad suggests retesting your child every one or two years to confirm the continued presence of food allergies, especially as diagnostic tools improve.