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Diagnosing Food Allergies

By HERWriter
 
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Food allergies are reactions by the immune system to certain foods. Most food allergies are diagnosed in children, but it is possible for adults to develop food allergies. Children who have food allergies sometimes outgrow the allergy. Adults who have food allergies will typically have the allergy for the rest of their lives.

Food allergies seem to have a regional component since the foods people are usually allergic to are those foods they eat often. So for example, rice allergy is more common in Japan while codfish allergy is more common in Scandinavia.

In order to diagnose a food allergy, the doctor must first rule out other health problems that can cause similar symptoms. An allergist or immunologist is a doctor who specializes in caring for patients who have allergies. Your allergist will probably use a variety of tests to determine whether you have a food allergy and what you are allergic to.

History – A basic physical examination and asking questions about your health can help your doctor find out about your symptoms and what is normal for you. Your doctor will probably ask questions about your symptoms including when they started, what symptoms you notice and what food you believe might be a trigger for your symptoms. Timing of your reaction is important, so try to remember how long it took after you ate before you experienced symptoms and how bad the symptoms were. Also think about how the food was prepared. For example, do you always react to fish or only to undercooked or raw fish?

Diet Diary – If you can’t remember exactly what you ate or how quickly symptoms occurred, your doctor may ask you to keep a diary of what you eat. It is important to record everything you eat in your diary, not just the foods you believe are problematic.

Elimination Diet – This tool can help your doctor figure out exactly what foods you are allergic to. The diet starts with food choices that are generally considered “safe” because few if any people are allergic to them. Over several days or weeks, other foods will be added to your diet so you can watch to see which foods cause a reaction. This method of figuring out your allergens (things you are allergic to) may not be safe if you have a severe reaction and should only be tried under a doctor’s supervision.

Skin Test – In a scratch or skin prick test, your allergist will place tiny amounts of allergens on the thin skin on your lower arm or on your back. This may be done by scratching the surface of the skin before applying a drop of allergen or by using a needle to inject a drop of allergen just under the skin. Any allergens that you are allergic to will react within about 15 minutes by forming a small hive or welt on the skin right where they were injected. These hives will go away in about 30 minutes. This test will give your allergist specific allergens to consider. However, it is possible to have a positive reaction on your skin without being truly allergic to the substance. Your doctor will correlate the results of the skin test with other tests including your history of reacting or not reacting to that food when you eat it.

Blood Test – When skin testing is not possible because of a skin condition such as eczema or because the risk is too great, such as with a suspected severe peanut allergy, your doctor may draw blood in order to test for reactions in the lab. This method can also help clarify the results of a skin test if some allergens were not conclusive. Blood tests include the RAST (radioallergosorbent test) and the newer CAP-RAST. These tests check for food-specific substances in your blood known as Immunoglobulin E or IgE. You can read more about IgE in the article What Causes a Food Allergy?

Oral Food Challenge – This is the most conclusive test for a specific food allergy, but it is also the most potentially dangerous, depending how strong your reaction to the allergen is. In this test, you will eat a small amount of the food you may be allergic to under close medical supervision. You will then be observed for several hours to see if you have a reaction and how severe the reaction is. This test should only be done under your doctor’s supervision.

Testing for food allergies may seem like an unnecessary step. You may believe that you can tell what you are allergic to based on what you have eaten. Because foods are prepared in a confined area and often share cookware and storage space, it is easy for cross-contamination to occur. For example, some people who believe they are allergic to French fries or to the oil they are fried in later learn through testing that they are in fact allergic to some other food that was cooked in the same oil as the fries. Testing by an allergist is the only conclusive way to be sure you know exactly what foods to avoid to prevent an allergic reaction.

Sources:
National Institute of Allergy and Infectious Diseases
About.com: Top Five Methods for Diagnosing Food Allergies
American Academy of Allergy Asthma & immunology
A.D.A.M, Inc.

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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.

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