It has been my experience that food allergy tests can be a bit unreliable. It is best to use combinations of allergy tests to get the most accurate readings and results. Normally you will have to ask your child’s allergist to do more than one type of test. You can even request that your doctor order the results to be sent to more than one lab for more accurate readings. Further, consider getting a second opinion from a different allergist.
Sounds like a lot of work? Perhaps. But consider the impact of food allergies on your life and your child’s life. Eliminating a single food from your child’s or family’s diet can be a lot more work and for a much longer time. It can also contribute to stress in your life and in your child’s life because it affects both social life and school life. When food allergy testing normally comes around every year or two, it isn’t unreasonable to make sure the results are really accurate since you'll have to live with them for a long time.
The following is a summary of food allergy tests that you can seek out for your child. Due to the inaccuaracy rates of single tests, combining results can give you a clearer picture of your child’s situation. Further because different labs and doctors can produce different results from the same tests, don’t be shy about getting a second opinion. Call your insurance company about coverage for additional tests. Share the test results with all the doctors involved to they can learn as well. Any doctor who gets annoyed that you have asked for a second opinion does not have your child's health concerns first.
- Skin prick tests: This involves pricking the skin with various allergens. The benefit of this type of test is that it will probably not give a false negative meaning if the child has an allergy--it will appear. But the con is that it can give a false positive meaning that it may show an allergy when in fact the child can tolerate the food.
- Blood tests: Several types exist such as the RAST (Radioallergosorbent Test) and ELISA (enzyme-linked immunosorbent assay). The results can be misleading in that sometimes the child will be allergic to the food but the test will result in a negative result. The blood taken from the child’s arm can be split and sent to two different labs for more accurate results. You will need to request that this be done.
- Kinesiology tests: This is done by homeopathic physicians using a small vile of the allergen which is held in the hand of a patient while muscle strength is tested. It is a non-invasive non-painful test and easy to do--but the interpretive nature of the results may put some people off as to its validity.
- Challenge tests: This test involves eating the offending allergy-food in the doctors’ office. It is normally recommended when BOTH blood and skin prick tests are negative. It is a lengthy test (3-4 hours most of which is waiting) and is normally done when there is a very good chance the child has outgrown the food allergy.
- New tests in the future: “A new kind of blood test could someday help doctors zero in more definitively on who is most likely to have allergic reaction to foods. Phadia AB, a maker of allergy tests, has developed a test, called Component-Resolved Diagnostis (CRD) that can determine which molecule within a food is sparking the antibody reaction. In the peanut, for example, only three of 14 different molecules are associated with anaphylaxis-causing reaction, according to the company. CRD has not yet been submitted for approval by the Food and Drug Administration, but it is in use in Europe…In the Manchester study, for example, the researchers found that almost all of the children who were highly allergic to peanuts reacted to a specific protein call Ara h 2…Knowing more about what specific molecules cause allergic reactions could help scientists understand more about the severity of allergic reactions, and someday help efforts to develop treatments to trick the immune system into behaving differently.”
- Delayed allergy tests: Most allergy testing is for immediate allergies (with symptoms of hives, anaphylaxis, vomiting, breathing, swelling, rashes, eczema). But for many the symptoms are not so obvious--making the connection between cause and symptom downright difficult. Delayed food allergies can be tested for through blood testing (only) as described above. But instead of searching for IgE antibodies, the lab must look for IgG or IgA antibodies. You will need to find an allergist who is knowledgeable in this area. Parents and children dealing with asthma, autism and ADHD often have delayed food allergy antibodies.
In summary, take your child to an allergist for allergy testing. Ask for more than one kind of test and consider getting a second opinion. Share results among the doctors and labs. Understand that immediate allergies are different from delayed allergies, but both can affect a child's life drastically.
 Beck, Melinda, The Wall Street Journal, 1/26/2010, http://online.wsj.com/article/SB10001424052748703808904575025013194645130.html