Should My Child be Tested?
Your child could potentially be allergic to a large variety of different foods. However, common things happen commonly and the most likely foods that children develop allergies to are milk, soy, eggs, peanuts, tree nuts, fish, shellfish, and wheat. You should see and allergist and have your child tested for food allergies if any of the following symptoms have happened shortly after eating:
- hives or redness of the skin
- itchiness in the mouth or all over
- swelling of the lips or eyelids
- throat tightness, or changes in the voice
- wheezing, breathing trouble, or coughing
- vomiting, diarrhea or fainting
Remember that a person may develop a new allergy at any time so just because your child has eaten nuts before does not mean that the current reaction could not be from the nuts.
How is a food allergy diagnosed?
Your visit with the allergist will involve a detailed history of foods that your child has eaten and a determination of the severity of symptoms. The doctor will pay special attention to the presence of other allergic diseases like allergic rhinitis (hay fever), asthma and eczema.
If the doctor feels that the symptoms are consistent with food allergy then allergy skin tests for common food allergies will be performed. Usually from the history the most obvious culprit can be identified and testing to that food will be performed. It is not advised to have random food allergy blood testing to a whole battery of foods when there are no clear symptoms. The concern is that a result may be a false reading and your child will unnecessarily avoid foods.
What are the tests for food allergy?
There are a few different tests for food allergy. In general the allergist will perform the one of the following:
- Skin testing:
- Skin testing involves placing a small drop of a sterile food extract on the skin and pricking the skin with a small plastic testing device. These devices are typically preloaded with the food extract and are single use, disposable devices. These tests are usually done on the back or arm and results are available in about 15 minutes. If you are allergic then a small red itchy bump will appear at the testing site.
- Skin testing for allergies to things that your child may inhale (pollen, animal dander) may involve an intradermal skin test. In these tests a small amount of the substance is injected into the skin. This type of testing is not used in food allergy testing as there is risk for a severe allergic reaction.
- There is a general misunderstanding that these tests are painful and can not be performed on infants. Studies have shown that these tests are actually very well tolerated with minimal pain. Furthermore, skin testing can be performed at any age.
- Blood testing:
- Blood testing, commonly referred to as RAST testing is not performed as often as the skin tests but have value in certain settings. These tests measure the amount of the allergic antibody or IgE in the blood stream. Keep in mind that it is not the IgE in the blood that results in allergy but the IgE that has left the blood stream and has become attached to allergy cells called MAST cells. Your body will make this type of antibody when you are allergic. A skin test, as discussed above, is the test of choice to detect the presence of IgE attached to MAST cells. When skin testing can not be performed then the blood test will be performed.
- Commonly random screening tests to multiple foods will be performed on blood sample in search of a possible allergy. This practice is not advised as it frequently results in false positive reactions and unnecessary food avoidance.
- Food challenge testing:
- This type of testing should only be done in the office of an allergy specialist that is trained in managing severe allergic reactions. With this test increasing amounts of a food are given over time and you are observed for signs of a food allergy.
- Elimination diet:
- Your doctormay want your child to stop eating suspect foods for a week or two and then add the foods back into the diet one at a time. This process may help to identify specific foods causing certain symptoms. During this time it is important to keep a good food diary. If you have had a severe reaction to foods, this method cannot be used.
What do I do to prepare for food allergy testing?
You should ask your doctor if there are any medications that your child needs to avoid prior to the testing. Typically, with skin testing you will need to avoid certain medications such as antihistamines for several days prior to the tests. You typically do not need to stop any of your other regular medications.
What do I do if the tests are positive?
Your doctor will review the tests with you. If your child's tests are positive that means they are allergic to those foods and should strictly avoid them. If your child has had a severe reaction in the past your doctor may recommend you carry epinephrine injections and that they wear a medic alert bracelet or necklace.
At times this can be very difficult and you will need to learn how to read food labels very carefully.
Do all positives test mean that my child has food allergy?
This is a very difficult question to answer and you should discuss this in detail with a trained allergy specialist before you give your child a food that they could be allergic to.
However, tests can be falsely positive at times. This may especially happen when tests are done at random, in the absence of particular symptoms. Your child can sometimes continue to have a positive test result for many years to a food allergy that he or she has outgrown. Sometimes food allergy tests cross-react with related food proteins that your child is not allergic to. In this setting, the cross-reacting, or related food is positive but there is no true allergy.
Will my child out grow his or her food allergy?
At times a child may out grow a food allergy. Most commonly this occurs with foods like milk and soy. However, foods like peanuts and tree nuts tend to be life long. You should discuss this with your allergist in detail as repeat testing and possible food challenges will need to be performed to determine if the food allergy is no longer present.