Food Allergy Testing and Diagnosis

Your First Appointment

Your first step toward relief is to schedule an appointment with an allergist to receive a proper diagnosis. Your allergist will evaluate several things before making an allergy diagnosis, and it’s nice to know what to expect.

Your allergist will begin by taking a detailed medical history. They will ask detailed questions about your history of allergy symptoms, your diet, your family’s medical history, and your home and living area. Some questions your allergist may ask include:

• The symptoms you have after eating the food.
• How long after eating the food these symptoms occurred.
• How much of the food you had.
• How often the reaction has occurred.
• Whether it occurs with other foods.
• Whether it occurs every time you eat the food.
• What type of medical treatment, if any, you received after having symptoms.

These questions help your allergist find out what is causing your allergy or making your symptoms worse. For example, allergy to pollen in the air, such as ragweed pollen, can be the cause of the swelling or itching in your mouth and throat if you eat certain foods like melons.

Your allergist may recommend allergy tests, such as a skin test or blood test to determine if you have a food allergy. A sensitivity to a food can be indicated in a skin prick test or a blood test, but does not always show a true allergy unless there has been a previous reaction to the food. These tests may offer clues about the causes of symptoms, but they cannot determine whether someone has a food allergy with absolute certainty. If necessary, an oral food challenge may be used to positively confirm the food that is causing the problem.

When a food allergy is suspected, it’s critically important to consult an allergist, who can decide which food allergy tests to perform, determine if food allergy exists, and counsel you on food allergy management once the diagnosis has been made.

Elimination Diet

Your allergist may narrow the search for foods causing allergies by placing you on a special diet. You may be asked to keep a daily food diary. The diary lists all food you eat and medication you take, along with your symptoms for the day.

If only one or two foods seem to cause allergies, you may try avoiding them. In this diet, you do not eat the suspect food at all for one to two weeks. If the allergic symptoms decrease during that period and flare up when you eat the food again, it is very likely the food causing your allergy.

However, which food you should avoid (and for how long) and when you should eat the food again (if ever) should be decided together with your allergist. You should never try to eat even a small quantity of any food your allergist has determined may cause a risk of anaphylaxis.

Your allergist may want to confirm these diet tests with a challenge test. Food allergy testing is a very important step in diagnosing food allergies.

Food Allergy Testing

 If done correctly and interpreted by a board-certified allergist, skin tests or blood tests are reliable and can rule food allergy in or out.

Your allergist will interpret the test results and use them to aid in a diagnosis. While both kinds of testing can signal a food allergy, neither is conclusive. A positive test result to a specific food does not always indicate that a patient will react to that food when it’s eaten. A negative test is more helpful to rule out a food allergy. Neither test can predict how severely a patient will react if they eat a specific food. Some people test “allergic” to a food (by skin or blood testing) and yet have no symptoms when they eat that food.

Skin Testing

Skin prick tests are conducted in a doctor’s office and provide results within 15-30 minutes. A nurse or the allergist administers these tests on the patient’s arm or back by pricking the skin with a small, sterile probe that contains a tiny amount of the food allergen. The tests, which are not painful but can be uncomfortable (mostly itchy), are considered positive if a wheal (resembling a mosquito bite bump) develops at the site.

The size of a wheal does not necessarily predict how severe your reaction might be if you eat that food.

Blood Testing

Blood tests, which are less sensitive than skin prick tests, measure the amount of IgE antibody to the specific food(s) being tested. Results are typically available in about one to two weeks and are reported as a number.

The level of IgE antibodies found for a specific food does not necessarily predict how severe your reaction will be if you eat that food.

Oral Food Challenge

To confirm your test results, your allergist may recommend an oral food challenge, which is the gold standard for food allergy diagnosis. However, the procedure can be costly, time-consuming, and in some cases is potentially dangerous, so it is not routinely performed.

During an oral food challenge, the patient is fed gradually increasing amounts of the suspected allergy-causing food over a period of time under strict supervision by an allergist. Emergency medication and emergency equipment must be on hand during this procedure.

Oral food challenges may also be performed to determine if a patient has outgrown a food allergy.

Food Allergy Diagnosis

Diagnosing food allergies can be complicated. Symptoms of food allergy can vary from person to person, and a single individual may not always experience the same symptoms during every reaction. Food allergic reactions can affect the skin, respiratory tract, gastrointestinal tract, and/or cardiovascular system, and people may develop food allergies at different ages.

Your allergist will look at both your test results and your medical history to make a food allergy diagnosis. 

If you are diagnosed with food allergies, your allergist will prescribe an epinephrine auto-injector and teach you how to use it.

You’ll need to be careful to avoid eating foods you are allergic to. Ask your allergist what safety precautions you need to take.