Food Allergy Testing

What is food allergy testing?

A food allergy is a condition that causes your immune system to treat a normally harmless type of food as if was a dangerous virus, bacteria, or other infectious agent. The immune system response to a food allergy ranges from mild rashes to abdominal pain to a life-threatening complication called anaphylactic shock.

Food allergies are more common in children than adults, affecting about 5 percent of children in the United States. Many children outgrow their allergies as they get older. Almost 90 percent of all food allergies are caused by the following foods:

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

For some people, even the tiniest amount of the allergy-causing food can trigger life-threatening symptoms. Of the foods listed above, peanuts, tree nuts, shellfish, and fish usually cause the most serious allergic reactions.

Food allergy testing can find out whether you or your child has a food allergy. If a food allergy is suspected, your primary care provider or your child's provider will probably refer you to an allergist. An allergist is a doctor who specializes in diagnosing and treating allergies and asthma.

Other names: IgE test, oral challenge test

What is it used for?

Food allergy testing is used to find out if you or your child has an allergy to a specific food. It may also be used to find out whether you have a true allergy or, instead, a sensitivity to a food.

Food sensitivity, also called food intolerance, is often confused with a food allergy. The two conditions can have similar symptoms, but complications can be very different.

A food allergy is an immune system reaction that can affect organs throughout the body. It can cause dangerous health conditions. Food sensitivity is usually much less serious. If you have a food sensitivity, your body can't properly digest a certain food, or a food bothers your digestive system. Symptoms of food sensitivity are mostly limited to digestive problems such as abdominal pain, nausea, gas, and diarrhea.

Common food sensitivities include:

• Lactose, a type of sugar found in dairy products. It may be confused with a milk allergy.
• MSG, an additive found in many foods
• Gluten, a protein found in wheat, barley, and other grains. It is sometimes confused with a wheat allergy. Gluten sensitivity and wheat allergies are also different from celiac disease. In celiac disease, your immune system damages your small intestine when you eat gluten. Some of the digestive symptoms can be similar, but celiac disease is not a food sensitivity or a food allergy.

Why do I need food allergy testing?

You or your child may need food allergy testing if you have certain risk factors and/or symptoms.

Risk factors for food allergies include having:

• A family history of food allergies
• Other food allergies
• Other types of allergies, such as hay fever or eczema
• Asthma

Symptoms of food allergies usually affect one or more of the following parts of the body:

• Skin. Skin symptoms include hives, tingling, itching, and redness. In babies with food allergies, the first symptom is often a rash.
• Digestive system. Symptoms include abdominal pain, metallic taste in the mouth, and swelling and/or itching of the tongue.
• Respiratory system (includes your lungs, nose, and throat). Symptoms include coughing, wheezing, nasal congestion, trouble breathing, and tightness in the chest.

Anaphylactic shock is a severe allergic reaction that affects the entire body. Symptoms may include those listed above, as well as:

• Rapid swelling of the tongue, lips, and/or throat
• Tightening of the airways and trouble breathing
• Fast pulse
• Dizziness
• Pale skin
• Feeling faint

Symptoms can happen just seconds after someone is exposed to the allergic substance. Without quick medical treatment, anaphylactic shock can be fatal. If anaphylactic shock is suspected, you should call 911 immediately.

If you or your child is at risk for anaphylactic shock, your allergist may prescribe a small device you can use in an emergency. The device, which is called an auto-injector, delivers a dose of epinephrine, a medicine that slows down the allergic reaction. You will still need to get medical help after using the device.

What happens during food allergy testing?

The testing may begin with your allergist performing a physical exam and asking about your symptoms. After that, he or she will perform one or more of the following tests:

• Oral challenge test. During this test, your allergist will give you or your child small amounts of the food suspected of causing the allergy. The food may be given in a capsule or with an injection. You'll be closely watched to see if there is an allergic reaction. Your allergist will provide immediate treatment if there is a reaction.
• Elimination diet. This is used to find which specific food or foods is causing the allergy. You'll start by eliminating all suspected foods from your child's or your diet. You will then add the foods back to the diet one at a time, looking for an allergic reaction. An elimination diet can't show whether your reaction is due to a food allergy or a food sensitivity. An elimination diet is not recommended for anyone at risk for a severe allergic reaction.
• Skin prick test. During this test, your allergist or other provider will place a small amount of the suspected food on the skin of your forearm or back. He or she will then prick the skin with a needle to allow a tiny amount of the food to get beneath the skin. If you get a red, itchy bump at the injection site, it usually means you are allergic to the food.
• Blood test. This test checks for substances called IgE antibodies in the blood. IgE antibodies are made in the immune system when you are exposed to an allergy-causing substance. During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, 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. This usually takes less than five minutes.

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

You don't need any special preparations for a food allergy test.

Are there any risks to the test?

An oral challenge test can cause a severe allergic reaction. That's why this test is only given under close supervision by an allergist.

You may get an allergic reaction during an elimination diet. You should talk to your allergist about how to manage potential reactions.

A skin prick test can bother the skin. If your skin is itchy or irritated after the test, your allergist may prescribe medicine to relieve the symptoms. In rare cases, a skin test can cause a severe reaction. So this test must also be done under close supervision by an allergist.

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

What do the results mean?

If the results show that you or your child has a food allergy, the treatment is to avoid the food.

There is no cure for food allergies, but eliminating the food from your diet should prevent allergic reactions.

Avoiding allergy-causing foods can involve carefully reading labels on packaged goods. It also means you need to explain the allergy to anyone who prepares or serves food for you or your child. This includes people like waiters, babysitters, teachers, and cafeteria workers. But even if you are careful, you or your child may be exposed to the food by accident.

If you or your child is at risk for a severe allergic reaction, your allergist will prescribe an epinephrine device you can use if accidentally exposed to the food. You'll be taught how to inject the device in your or your child's thigh.

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

Is there anything else I need to know about food allergy testing?

The best way to prevent an allergic reaction is to avoid the food you are allergic to. But there are some new therapies which might help prevent a severe reaction if you are accidentally exposed to the food you are allergic to. These include:

• Oral immunotherapy (OIT). This involves eating a small amount of an allergy-causing food and gradually increasing the amount. The goal of this therapy is to increase the amount of food that can be eaten before causing an allergic response.
• Epicutaneous immunotherapy (EPIT). This is similar to OIT, but instead of eating a certain food, a protein from that food is delivered through a skin patch. The patch is replaced daily with increasing larger amounts of the protein. 

Both OIT and EPIT are always done under close medical supervision. To learn more about these approaches, talk to your allergist. 

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