Diagnosing Food Allergies With Your Doctor's Help

Your doctor will question you about your reactions and perform tests

To diagnose food allergies, your doctor first will talk to you about your reactions to certain foods, and then may perform several tests that can provide information on your body's reaction to those foods. Ultimately, she will use all this information to diagnose you with food allergies.

It is estimated that at least 15 million people have food allergies, which can affect everyone, from infants to seniors. In fact, someone can develop a food allergy at any stage of life.

While some allergies can be outgrown, others cannot. The eight most common food allergens, which include milk, wheat, peanuts, tree nuts, crustacean shellfish, soybeans, fish, and eggs, account for more than 90 percent of all food allergies.  However, make no mistake about it: it's possible to be allergic to many other foods. 

Diagnosing Your Food Allergies

Food allergies are never something you can ignore since they can become life-threatening. You always should have symptoms checked out by your doctor. For example, suppose you feel your tongue getting tingly shortly after you eat some strawberries, or your child gets hives after eating whole grain waffles every day for breakfast—both of those are potential symptoms of an allergic reaction to food.

While food allergy symptoms can range from relatively minor issues (such as headaches, hives, and runny noses) to more serious issues (like difficulty breathing), none of them should be ignored, because the second exposure to the allergen—and your reaction to it—can be much worse than the first.

Therefore, if you experience any symptoms that could be food allergies, you should talk with your doctor or allergist. Depending on your symptoms, your doctor will determine the best course of action to diagnose those potential allergies. If you do have a food allergy, you'll then be able to focus on removing that food from your diet.

There are many tools and methods that your doctor can use to determine which foods or substances may be causing your allergic symptoms. Below are the most common methods used to identify food allergies.


Medical History

Your first visit to the doctor to discuss your allergy symptoms will probably begin with a physical examination and a history. Both the exam and your medical history will provide clues that can help your doctor determine what food (if any) may be causing your reactions.

Your physician may ask you when your symptoms began, what sorts of foods you ate around the time they started, and what changes you may have experienced in your home, work, or school environments. Sometimes an event that seems like a minor change (such as switching cereal brands) can provide a clue to your allergy, so try not to overlook anything.

Prior to your doctor's appointment, you also may want to consider keeping a food diary to show to your physician. This diary should list foods you eat, the times you eat them, plus any suspected symptoms.

In almost all cases, your doctor will supplement your medical history with diagnostic testing. The history can help allergists pinpoint potential allergens on which they should focus, or choose which testing methods might be most appropriate.


Prick Tests

Allergy prick tests

A prick test (also called a scratch test or a skin test), is often used to test a number of potential allergens at one time. Despite the name, this isn't a painful test, and it can provide a lot of information fairly quickly.

To perform a series of prick tests, your allergist will use either the thin skin of your forearm or your back. A drop of a solution that includes the food allergen is placed on the arm. The allergist scratches the skin to allow for a very minimal amount of the solution to enter just below the surface.

If the test is positive, you'll develop a hive, or wheal, in the area of the prick or scratch. A wheal is a raised white bump surrounded by a circle of itchy skin.  

All prick testing is done within your doctor's office, under close supervision, in case you have a serious allergic reaction.

Prick tests can provide lots of useful information, but sometimes they simply raise questions. An inconclusive prick test will usually be followed by a more sensitive test.


ELISA Testing

lab technician with blood tests
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ELISA tests (ELISA stands for "enzyme-linked immunosorbent assay") are blood tests. Your allergist will use ELISA tests to look for evidence of an immune system reaction to an allergen directly in your blood.

To perform an ELISA test, your doctor will draw a sample of your blood. In the lab, the blood will be mixed with a chemical that causes a color change if your immune system is reacting to a specific allergen, such as peanuts.

With an ELISA test, you never have to be exposed to the allergen directly—instead, your blood is exposed to it in the lab.

These blood tests are accurate and can help in situations where a skin test isn't recommended—for example, to determine if a child has outgrown a serious allergy.

However, they do have some downsides: they're more expensive than skin prick tests, and they take days or weeks (as opposed to minutes) to produce results. Nonetheless, your doctor may recommend performing ELISA tests in order to get an accurate diagnosis.


RAST Tests

Taking blood sample
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The RAST or radioallergosorbent, test is a blood test that tests for IgE antibodies. Although most physicians have switched to the newer, more accurate ELISA test, some still prefer RAST tests under certain circumstances.

Like the ELISA test, the RAST test can be used when a skin test would be difficult to perform (for example, in a patient with severe eczema or another skin condition) or where exposing the patient to an allergen might be unnecessarily risky (for example, in cases of suspected severe peanut allergies).

A positive test result indicates that the body has produced antibodies to an allergen and is primed for a reaction.


Elimination Diet

As you probably assumed from the name, an elimination diet has you eliminate potentially allergenic foods and then reintroduce them to see if you react to them.

An elimination diet can be undertaken in several ways, depending on the allergist supervising it.

Still, the basic principle is the same: you'll begin with a limited set of foods that are deemed unlikely to cause a reaction, and then add other foods gradually, one by one, over a period of days or weeks.

While the elimination diet can be tedious, it can be an effective way to determine which substances are problematic, especially when skin testing is inconclusive. It also can help diagnose food intolerances, which may cause problematic symptoms but will not show up on an allergy test.


Oral Food Challenge

food allergens
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In a food challenge, patients ingest suspected allergens and are observed over a number of hours to determine whether they have an allergic reaction.

An oral food challenge is risky and always should be carried out under close medical supervision, but it will show the presence of an allergy conclusively. You should never attempt an oral food challenge without consulting with your doctor since you could have a serious allergic reaction.


A Word From Verywell

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Diagnosing food allergies can seem a bit like putting together a puzzle: your doctor will need all the pieces to get an accurate picture, and you'll need to contribute by keeping an accurate food diary (if needed) and participating in testing. While the diagnosis may be quick, it also may take some time.

Still, once you have an accurate diagnosis and have eliminated the problematic allergenic food, you'll be able to stop your reactions and improve your health.

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Article Sources

  • American College of Allergy, Asthma, and Immunology. Food Allergy Testing fact sheet.