Food allergy can be difficult at times to understand. Food allergy is overestimated as there is a general misconception that any reaction to a food is an allergy. Adverse reactions to food can be simply classified as food allergy and food intolerance. A true food allergy is an immune reaction due to the presence of a specific IgE antibody to the food. A food intolerance is not due to allergy but may have other reasons. The most widely recognized food allergies are to peanut, tree nuts and shellfish. An example to a food intolerance is the reaction to lactose due to the inability to digest this milk sugar causing gastrointestinal symptoms.
The evaluation of an adverse reaction to a food begins with a thorough patient history of the reaction. The history will determine what tests should be ordered. In IgE based food reactions, the suspected food can be evaluated by either a prick skin test, or if this is not possible a blood test that will identify the IgE to that food.
Evaluation for a food allergy should be as specific as possible to the history of the reaction and not a general screen as false positive finding may be seen. An accurate specific diagnosis is necessary as the treatment for a food allergy is strict avoidance and having the availability of epinephrine as life threatening reactions are possible.
Other reported blood test are sometimes ordered but the only established test that has proven to be valid is the screen for Celiac disease. Other testing may evaluate IgG to foods which is not associated with food allergy.