An estimated 11 million Americans suffer from food allergies, which accounts for roughly 20,000 emergency room visits annually. And, unfortunately, as many as 200 people die from food-allergy reactions each year. But, food-allergy and intolerance are not the same.

Food intolerance is an undesirable reaction to a food that does not involve food-related immune response. The most common food intolerance is lactose intolerance, where the individual lacks an enzyme needed to digest milk sugar. When milk products are ingested, symptoms such as gas, bloating, and abdominal pain may occur. However, if only a small amount of milk is consumed, he or she may avoid the symptoms.

A food allergy occurs when a person with particular genetic predisposition produces specific immunoglobulin E (an allergy antibody) to the protein of a certain food.
When those antibodies react with a certain food, histamine and other chemicals are released from the body and cause allergic symptoms. Even when you only eat a small amount of allergy causing food, a reaction can be triggered. Although an individual could be allergic to any food, the following foods-tree nuts, eggs, soy, milk, wheat, fish and shellfish-account for 90 percent of all food-allergic reactions.

Food-allergy reactions can affect several body systems such as the gastrointestinal tract (abdominal pain, diarrhea, nausea, vomiting), skin (hives, eczema), respiratory system (swelling of the throat or mouth, wheezing, difficulty breathing) and cardiovascular system (drop in blood pressure, feeling of impending doom, loss of consciousness).

Urticaria (hives) is an outbreak of red bumps of patches called "wheals" that appear on the skin, produced by the presence of histamine and other chemicals. . Foods suspected of causing acute (sudden) hives are often identified by their ingestion on several occasions followed by a skin rash.
Chronic hives, which lasts more than three months, is not commonly just caused by a food allergy.

The most dangerous allergic reaction is known as "anaphylaxis" and can produce shortness, wheezing, airway swelling, increased heart rate, loss of consciousness, and even death. Both usually occur within minutes or can be delayed up to two hours after ingestion of the offending food. Peanuts are the leading cause of anaphylaxis, followed by shellfish, fish, tree nuts, and eggs. It is recommended that peanut-allergic patients avoid all tree nuts (pecans, walnuts, almonds, etc.), and vice versa, as an extra precaution.

In addition to food, medications, stinging insects, latex, and even extreme temperature change can cause urticaria or anaphylaxis

Diagnosis of food allergy not an easy task

Most causes of food allergy occur when a person with a particular genetic predisposition produces specific immunoglobulin E (allergy antibody) to the protein of a particular food.
When these IgE antibodies react with certain food, it triggers the release of histamine another various chemical from inflammatory cells, causing allergic symptoms that typically appear within minutes to two hours after a person has eaten the food to which he or she is allergic.
Moreover, there are some food allergies that are not meditated by IgE, such as food protein induced gastrointestinal disorders in children.

Although all foods can cause an allergy, tree nuts, eggs, soy, milk, wheat, fish, and shellfish account for 90 percent of all food allergy reactions. Less common additives such as dyes, sulfites, parabens, monosodium glutamate, butylated hydroxyanisole (BHA), butylated hydroxytolune (BHT), and nitrates also can cause allergic reactions.

Commonly used tests are the blood RAST (radio allergosorbent test) and the CAP ELISA (enzyme linked immunoabsorbent assay) as well as skin prick testing. Both the blood tests and skin prick testing determine the presence of a specific IgE antibody directed to particular foods.
Even if specific IgE is detected, a definite diagnosis cannot be simply based on positive specific IgE results, as up to 50 percent of patients with positive IgE tests do not in fact have allergy to a particular food. Therefore, a positive prick skin test does not necessarily mean that the patient will experience an allergic reaction to certain food. The upside to these results is that negative tests are very reassuring that the food can be ingested safely without experiencing IgE-mediated food allergy. Still, negative tests cannot exclude the possibility of non-IgE mediated food allergy.

The key to food allergy testing is that your allergist must interpret the test results while keeping your complete medical history in mind. Sometimes, even when taking these factors (skin prick test, blood test, and medical history) into account, your allergist still cannot make a definite diagnosis. Therefore he or she may recommend a food challenge: asking you to eat gradually increasing amounts of the suspected food under the physician's supervision while he or she observes you for any symptoms.

While food challenges can offer definite answers, they also can carry the risk of a serious reaction during a challenge. Sometimes, a food challenge is the only definite way to make a correct diagnosis, particularly if a food additive or a non-IgE mediated food allergy is present. They will not produce positive skin tests or positive blood tests.

Diagnosing food allergy is not an easy task, and it requires teamwork. In addition to skin and blood tests, your detailed medical and dietary histories are crucial for a final diagnosis.

By Dr. Yong H. Tsai
Published in The Daytona Beach News-Journal
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