Allergy Testing
There are basically three main types of allergy tests that can be done for children or adults showing signs of possible food allergies.  The first method is the RAST test. RAST stands for radioallergosorbent testing. Blood is drawn from the patient and sent to a lab for evaluation. There are a couple of specific things that are looked at in the patient’s blood profile. The first thing is the IgE count. Active IgE is an antibody found only in people who have developed allergies. Suspected allergens are introduced into the blood to see if the IgE cells surround a mast cell. IgE surrounded mast cells are what produce histamine. Histamine is produced in a person's body when there is something the body sees foreign (an allergen) and attempts to cut if off by attacking it. This in turn causes symptoms such as swelling and nasal drainage, watery eyes, sneezing, wheezing, coughing, hives, and in some cases, anaphylaxis.
As the mast cells attach to the allergens, it is easy to discover which offending food is the culprit. The blood is "rinsed" and the clusters of allergens surrounded by histamine are left behind. This way the technician can easily define which particular foods have developed IgE antibodies. These are the foods that must be avoided. One advantage of the RAST test is there are no adverse reactions to the patient, because only the blood is being used. The results are also pretty accurate. The only downside is the possibility of "false positives". For instance, if you are allergic to peanuts (a legume, not a true nut) you might show a positive result for other legumes such as soy and snow peas as well.
The second type of testing is known as Skin Testing. There are different ways to perform this test, however in each method the skin is injected with a small amount of the suspected allergen in the doctor’s office. Within 15 minutes, you should know which of the allergens are positive, as there will be a swelling at the injection site, much like a bee sting. The hives are then measured to see how severe the allergies are. The advantage to this type of testing is the immediate knowing of which foods to avoid. In this case as well, there is a possibility of having "false positives". If you are allergic to almonds, you may appear to have an allergy to peaches, which are in the same family. You may be able to eat peaches freely on the other hand, but go into anaphylactic shock if you eat a pastry that has almonds.  Probably the most accurate and the most controversial of all, is the food challenge test. This is when the patient is fed the suspected allergen in a controlled and well-supervised medical setting. If a person has an allergic reaction, there is a trained team ready to handle the situation. If there is no reaction, you can assume that particular food is safe. Your allergist can recommend what he or she thinks is best in your particular situation, and it is very important to have a close relationship with one another to achieve the most benefit to you. I personally would discourage ANY form of food challenge at home. You must have proper medical supervision to avoid a potentially deadly situation.