There are several ways to diagnose a food allergy, including medical tests, food challenges, elimination diets, and self-screening. Mild allergies can be difficult to diagnose, but if your reaction has been severe the suspect food can usually be quickly identified.

Start with Yourself

A self-screening test can be helpful, and is usually the first step toward an accurate diagnosis. Start keeping a food diary, and carefully observe and record your symptoms: when they occurred; which foods you have eaten and how much you consumed; time from eating the food to when symptoms appeared; and the severity of symptoms.

Visit the Doctor

Most people visit their regular doctor when they are just not feeling well. You may have had digestive problems, skin irritation, breathing problems, depression, or tiredness and weakness. Your doctor will do a general workup on you, and if you are in general good health, the sleuthing begins.

When you begin the journey to diagnosis, find an allergy specialist. General practitioners and internists do not have the experience in diagnostic tools and treatments that specialists do. General practitioners can do preliminary work and exclude some diseases, but when interpreting test results, a specialist is more qualified.

The following organizations can help you find a qualified specialist:

• American Academy of Allergy, Asthma and Immunology

• American Board of Medical Specialists

• American College of Allergy, Asthma and Immunology

• American Board of Allergy and Immunology

• National Institute of Allergy and Infectious Diseases

Get Tested

There are two basic types of medical tests used to diagnose allergies: skin tests and RAST (radioallergosorbent test), which is a blood test that looks for the presence of IgEs specific to different foods. Your IgE number must be above a certain threshold for diagnosis of a food allergy.

The skin-prick test, while less accurate than the RAST, is also less expensive and faster. A solution containing the suspect proteins is scratched onto the skin, along with a control of salt water. The size of the reaction determines the allergy, with a negative reaction being the most accurate diagnosis. With a statistically significant positive skin test, the RAST test is the next step.

For the RAST (also called CAP-RAST and ImmunoCap test), blood is drawn and is tested against the different antigens from the suspect food. If IgEs are found with numbers above a certain threshold, a diagnosis of a food allergy is made. The higher the score, the more accurate the diagnosis. Doctors have set thresholds (in KUA/L, or kilounits of antibody per liter) above which there is a 95 percent chance that you do have an allergy to that food.

95 Percent Diagnostic Certainty CAP-RAST Test (0 to 100)

Other Tests

The elimination diet is a less scientific, but simple, way of determining food allergies when medical tests are inconclusive or contradictory. With this diet, which should be planned with the help of a nutritionist to make sure the diet is wholesome and meets all your needs, you are started on some hypoallergenic foods, including rice, bananas, vegetables, millet, and lamb.

Once you start feeling better, other foods are added slowly, at the rate of one every few days to a week. This is called the challenge phase of the diagnosis. If symptoms appear, the suspect food can be identified. Use of a food diary is critical during this test. If allergy reactions have been life threatening, this test should only be conducted in a physician's office where there are appropriate remedies.

The rotation diet is another possible diagnostic tool. In some people with less severe allergies, the rotation diet may be used to prevent future allergies. It can also uncover allergies to other foods, including corn, tomatoes, strawberries, and yeast. In the rotation system, a very strict diet of only a certain number of biologically related foods is eaten every day for four or five days.

The premise is that “masking antibodies” your body produces for a food will diminish in that time frame, because your immune system “rests” when not exposed to those allergens. This diet should not be followed long term because it limits entire food groups necessary for good health.

Some doctors think this diet does not work. It is very limiting and can be quite challenging to maintain. While the diet may be a diagnostic tool, claims that it can cure food allergies should be viewed with skepticism. Only you and your doctor can decide if a rotation diet is a good tool for you.

Now What?

Once you have a firm diagnosis, it's time to start learning which foods you must avoid and how to prepare for any potential reactions. Your doctor may prescribe an emergency kit including oral antihistamines along with an Epi-Pen, which is a small syringe filled with epinephrine.

It's important that you review the instructions with this kit, and even stage a mock emergency so you understand how to use the kit and can implement the medication as quickly as possible. If your child is allergic, you must inform all of the key people in his life about the allergy, so they can eliminate these foods and watch for symptoms of a reaction.

Not only should you educate yourself and your family about your allergy, but you have to educate the community you live in. Wear a medical-alert bracelet, let those close to you (teachers, friends) know about the allergy, and keep an emergency kit on hand to live well with allergies.

Ask your doctor for a list of words and terms that cover your food allergy and bring it with you when you shop and when you eat in restaurants. Become familiar with these terms so you know what to look for when reading food labels.