From Allergy Asthma Network's Ask an Allergist
First it's very important to see the right doctor for Food Allergy Testing, which is a board certified Allergist. They will ask about your medical history to see if it is consistent with a possible food allergy. The allergist can then determine the specific allergens to test.
Allergy testing for foods can be done either by skin prick testing, or by testing the blood for specific IgE directed against the potential food allergen. Both tests provide reliable results, although there’s not always complete agreement in the results between the two tests. Some allergist choose to use both tests in their practice.
The skin test provides almost immediate results with a small, localized reaction that you can actually see. Follow up can be done with a blood test that gives an actual IgE level for the food (or other allergen). The blood test can then be tracked every 6-12 months to determine whether or not the person is outgrowing the allergy (typically more common in children)
Interpretation of blood test results for food allergy can be tricky. A very low positive result is not always clinically relevant, and an allergist’s input can be helpful in determining which foods should be eliminated from the diet.
If the reactions are restricted to eczema (40% of eczema patients have food allergies) then elimination of those foods that tested positive can be helpful. If the clinical relevance of the positive test is unclear, gradual reintroduction (per your doctor’s instructions) of one food at a time can help determine which foods are contributing to eczema.
However, if the person has experienced an allergic reaction not related to an eczema flare, then reintroduction of a food allergen at home without medical supervision could be dangerous.
People with food allergies are prescribed two epinephrine auto-injectors and urged to avoid the food allergen in their diet. Allergist should follow the blood test results to determine whether the person's IGe level is decreasing. If the doctor thinks that it may be safe to reintroduce a food, usually they do an in-office food challenge under medical supervision before clearing the person to eat the food at home.