IgE mediated "fixed" food allergies are easily diagnosed with either skin or blood tests.
When food-specific IgE blood tests and skin tests are negative, then the following could be recommended:
- Elimination diets eliminate suspected food(s), prescribe a limited "eat only" diet, or offer an elemental diet. This diet usually lasts between one and six weeks.
- Oral challenge testing (physician supervised, with emergency medications available) can be open, single-blind, or double-blind, placebo-controlled. If the results indicate an IgE-mediated allergy, then the test for specific-IgE antibody could be negative (thus, reintroduce food) or positive (start the elimination diet). If the elimination diet provides no resolution, then reintroduce the food.
- Elimination/Challenge testing. The diagnostic approach for non-IgE-mediated disease includes disease with unknown mechanisms, such as food additive allergy. Elimination diets may be called for, and parent should search for hidden ingredients (peanut in sauces or egg rolls), labeling issues ("spices"), cross contamination (shared equipment), and "code words" (such as "natural flavors"). A registered dietitian should also be consulted. We typically eliminate the food for 5 days and then reintroduce it to look for the return of symptoms.