Food Allergy Testing

What is food allergy testing?

A food allergy happens when your immune system (your body's defense against germs) mistakenly reacts to a certain food as if it was harmful. This response can cause mild to severe symptoms. If you or your child has symptoms after eating certain foods, food allergy testing can help find out if your symptoms are caused by an allergic reaction to those foods.

Most food allergies are caused by:

• Milk
• Eggs
• Peanuts
• Tree nuts (including almonds, walnuts, pecans, and cashews)
• Soy
• Wheat
• Fish
• Shellfish

Food allergies are more common in children than adults. Most children will grow out of allergies to milk, egg, soy, and wheat. Allergies to peanuts, tree nuts, fish, and shellfish are more likely to last into adulthood. If a food allergy begins in adulthood, it's likely to continue through life.

If you or your child has symptoms that could be from a food allergy, your or your child's health care provider will probably refer you to an allergist for testing. An allergist is a doctor who specializes in diagnosing and treating allergies and asthma.

The allergist will pick the type of food allergy test that's right for you or your child. These tests include:

• Skin tests. In these tests, a provider will place a drop of liquid on your skin. Then, they will either lightly scratch or prick your skin so that the liquid can enter your body. This liquid will contain a protein from a specific food that may trigger an immune reaction.
• Allergy blood tests. In these tests, your provider measures the amount of immunoglobulin E (IgE) antibodies in your blood. Antibodies are proteins that your immune system makes to fight foreign substances, such as viruses and bacteria. Your body makes specific types of IgE in response to different foods. If you have an allergy, your levels of IgE related to that food may be higher than normal.
• Elimination diets. For this test, you will first remove all suspected foods from your diet. Then, you'll slowly start adding those foods back into your diet, one food at a time. By focusing on only one food, you may be able to tell which food is causing an allergic reaction.
• Oral food challenges. For this test, your provider will ask you to slowly eat increasing amounts of a food that's suspected of causing your symptoms. Your provider will watch you closely to see if you have an allergic reaction.

Other names: IgE test, sIgE test, allergen-specific IgE in serum, skin prick test (SPT), oral challenge test

What is it used for?

Food allergy testing is used to help find out if you or your child has an allergy to a specific food, but it's usually only ordered if you or your child has had symptoms of an allergy. That is because when used on people who don't have any symptoms, these tests can show signs of an allergy when there isn't one (known as a false positive result).

Food allergy tests can cause false positives because they are incredibly sensitive. They may, for example, find evidence of IgE in your blood and mistake that for an allergic reaction even though no allergic reaction is taking place. IgE may only be present in the blood because the food being tested is similar to a food you may actually be allergic to.

Most food allergy symptoms are mild and include skin rashes and abdominal (belly) pain. But sometimes, symptoms quickly develop into a life-threatening allergic reaction called anaphylaxis, or anaphylactic shock. Anaphylaxis is a life-threatening allergic reaction that may appear within minutes to hours after exposure to certain foods. It can cause trouble breathing, a rapid heart rate, and other symptoms.

If someone has symptoms of anaphylaxis, call 911 to get medical help right away.

There's no way to predict when an allergic reaction may change from mild to severe. Because of this, it's important to find out if you or your child have a food allergy as soon as you or your child starts having any of the symptoms of an allergy.

Testing may also be used to:

• See if allergies have gone away over time
• Tell whether your symptoms are being caused by a true food allergy or by a food intolerance or food sensitivity

Food intolerances and sensitivities can cause similar symptoms to those of an allergy. The key difference is that:

• Allergies involve your immune system, while intolerances and/or sensitivities usually only affect your digestion.
• Allergies can become life-threatening, while intolerances and/or sensitivities rarely are.
• Allergic reactions can be caused by even a small amount of a certain food, while intolerances and/or sensitivities may only cause symptoms if you've eaten large amounts of a certain food.
• Symptoms of an intolerance and/or sensitivity tend to be the same every time you or your child is exposed to a certain food. Symptoms of an allergy, on the other hand, can vary.

Examples of food intolerances, or food sensitivities, include:

• Lactose intolerance
• Gluten sensitivity
• Caffeine intolerance
• Irritable bowel syndrome

The symptoms may include belly pain, nausea, gas, and diarrhea, which can also happen with food allergies.

Why do I need food allergy testing?

You or your child may need food allergy testing if either of you have symptoms of an allergy within minutes to hours after exposure to certain foods. Symptoms may affect your digestion, skin, and/or breathing. These can include:

• Nausea and vomiting
• Stomach pain
• Diarrhea
• Tingling in the mouth
• Skin reactions, such as hives or itching
• Red, itchy skin or a rash
• Coughing
• Stuffy, itchy, or runny nose

You or your child may also need a food allergy test if either of you have had symptoms of anaphylaxis. Symptoms include:

• Trouble breathing
• Dizziness
• Fainting
• Swelling of the tongue, lips, and/or throat
• Rapid heart rate
• Cold, clammy skin that may appear grayish, bluish, or pale

Lastly, you or your child may have food allergy testing if you or your child has been diagnosed with eosinophilic esophagitis (EoE). This condition is a long-term immune system disease that causes inflammation in your esophagus (the tube connecting your mouth to your stomach). Testing is done to find out which foods may make this condition worse.

Your child's provider may recommend food allergy testing if your infant or child has been diagnosed with:

• Moderate to severe eczema
• Enterocolitis, inflammation of the colon and small intestine
• Enteropathy, a disease of the intestine
• Allergic proctocolitis, a disorder that involves streaks of blood and mucus in stool (poop)

What happens during food allergy testing?

A provider, often an allergist, will ask about your or your child's symptoms, family health history, and medical history, including other allergies. A physical exam is usually done before allergy testing.

Next, your allergist or another provider will do one or more allergy tests. There are many types of allergy tests, and they have different risks. So, ask your provider which tests are best for you or your child.

For a skin prick test:

• Your provider will first place a drop of liquid on the skin of your arm or back. The liquid contains a protein from a specific food that may trigger an immune reaction.
• The provider will then prick the skin under the drop so the liquid gets below the surface.
• You or your child will then wait for 15 to 30 minutes.
• If a red, itchy bump forms, you may have an allergy to that food. More than one food protein may be tested.

For an allergy blood test, a health care professional will insert a small needle into a vein in your arm. A small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out.

For an oral food challenge test, you will slowly eat increasing amounts of a food that's suspected of causing your symptoms. A healthcare professional will watch you closely for an allergic reaction. If your body doesn't react to the food, you aren't allergic to it. If you have an allergic reaction, your allergy is confirmed, and you'll be treated right away for the reaction.

For a food elimination diet:

• You'll start by removing all suspected foods from your diet for about two weeks.
• You'll then start adding the foods back into your diet, one at a time.
• If you have symptoms when you start eating a food again, you may be allergic to that food.
• Your symptoms could also be caused by a food intolerance, so other tests may be needed.
• A food elimination diet may not be safe for someone who has had a serious allergic reaction to food in the past.

Will I need to do anything to prepare for the test?

If you are having any type of allergy test, you may need to stop taking certain medicines and/or supplements before the test. Your provider will let you know what to avoid and for how long. Don't stop taking any medicines unless your provider tells you to. Your test may require other preparation, so be sure to follow all your provider's instructions for getting ready.

Are there any risks to the test?

A skin prick test can cause itchy or irritated skin. Your allergist may recommend medicine to relieve the symptoms. The test is generally safe, but a severe reaction is possible.

A blood test has very little risk. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

An oral challenge test can cause a severe allergic reaction. That's why this test is done with close supervision by an allergist who can treat you if there is an emergency.

An elimination diet may cause a serious allergic reaction. Ask your allergist what to do if you develop symptoms.

What do the results mean?

A food challenge test is the only food allergy test that can confirm a diagnosis of a food allergy. If you have other tests, your or your child's allergist will use your test results along with your symptoms and medical history to make a diagnosis.

If you had a blood test, your results may show the amount of IgE in your blood. This amount can't confirm a food allergy or tell you how serious an allergy may be. To confirm if you have an allergy, your provider will have to use the results from other tests.

If the allergist diagnoses a food allergy, the treatment is to avoid the foods that trigger your symptoms. There is no cure for food allergies. Avoiding trigger foods involves carefully reading food labels. You'll also need to explain the allergy to anyone who may prepare or serve food to you or your child, including friends, waiters, babysitters, and teachers.

Your allergist will tell you how to manage a mild allergic reaction. In case you or your child has a severe allergic reaction, your allergist may prescribe an autoinjector. An autoinjector is a small device that you use to inject an emergency allergy medicine, called epinephrine. If you need to use the device, it's still very important to get medical help right away even if you feel better. Your allergist will explain when and how to use an autoinjector.

If you have questions about test results and/or how to manage allergic reactions, talk with your allergist.

Learn more about laboratory tests, reference ranges, and understanding results.