About the Test
Purpose of the test
Oral food challenges are used in the diagnosis of food allergies. As some patients can outgrow their food allergies, the test can also check if those allergies have improved or resolved. Determining the presence of a food allergy is very important because some allergic reactions can be severe or life-threatening and require treatment. This test is not used to determine the severity of an allergy.
Although any food can cause an allergy, the majority of food allergies come from these eight categories:
- Eggs
- Fish
- Milk
- Peanuts
- Shellfish
- Soy
- Tree nuts
- Wheat
Your doctor determines what food will be used in your oral food challenge based on your medical history and any prior allergy testing.
What does the test measure?
An oral food challenge measures whether a person has an immune reaction to a specific food. This is determined by whether or not symptoms occur when the challenge food is eaten.
Although the person’s response to the challenge food can provide information about the strength of their reaction, this test is not used to determine the severity of an allergy.
When should I have an oral food challenge?
Your health care provider may suspect that you have a food allergy after hearing your medical history and reviewing prior allergy test results. You may be asked to undergo an oral food challenge to confirm the diagnosis of a food allergy or to determine whether a food allergy has resolved.
Food allergy symptoms may include:
- Hives
- Wheezing
- Swelling, particularly in the face
- Trouble swallowing
- Itching
- Runny nose
- Digestive issues, such as cramps, vomiting, and diarrhea
- Anaphylaxis, a severe and potentially life-threatening reaction involving multiple body systems
If you have any of these symptoms, you should talk with your health care provider who can help determine what type of testing is most appropriate.
Finding an Oral Food Challenge
How to get tested
Typically, an allergist, a doctor who has specialized training in allergies and other immune disorders, performs oral food challenges. However, because food allergies can also impact the digestive system, the test is sometimes done by a gastroenterologist, a doctor who has specialized training in conditions that affect the digestive tract.
Oral food challenges are typically performed in a doctor’s office or clinic once a medical exam and evaluation of your medical history, including the results of any allergy blood tests or allergy skin tests, have been completed.
Can I take the test at home?
Oral food challenges should not be performed at home due to the risk of serious allergic reactions. Health care providers who are trained to treat these reactions and evaluate the results should perform this test. Do not attempt an oral food challenge on your own.
How much does the test cost?
The cost of an oral food challenge may include office visits, testing supplies, and medications after the test. Certain types of oral food challenges can involve additional medical staff to oversee the test, which may also affect the cost.
Insurance may cover the cost of testing, though you may be responsible for a copay or deductible. Your doctor and insurance company can give you details about your coverage and costs.
Taking an Oral Food Challenge
In an oral food challenge, small amounts of a suspected food allergen are eaten to determine if symptoms occur. No blood or tissue samples are collected for this type of allergy testing.
Before the test
In order to get accurate results, your doctor will provide you with directions for how to prepare for your specific test. These instructions may include:
- Avoid the food to be tested for several weeks prior to the challenge
- Do not eat or drink anything for a minimum of two hours in advance of the test
- Stop taking certain medications as directed by your physician
It is important that you be in good health on the day of the test. If you feel unwell, you should contact your doctor to discuss rescheduling.
You should bring your allergy medications to the test, including any emergency or rescue medications such as injectable epinephrine. Depending on what is being tested, you may be asked to bring the challenge food with you.
During the test
An oral food challenge begins with a basic physical exam to establish a baseline to which any reactions will be compared.
In the test, you eat the challenge food and are checked for a reaction. You start with a small amount and, if your doctor determines there is no reaction after 15-30 minutes, you have a slightly larger amount. This process continues until there is a reaction or until you have eaten a meal-sized portion of the challenge food. If you have a reaction, the test is stopped and you are given medication to treat your symptoms.
The oral food challenge will be administered in one of three ways: open, single-blind, or double-blind.
In an open challenge, you will know when you are eating the challenge food. Typically, it is in its natural form, such as peanut butter or tofu. This is the most common type of oral food challenge given in doctors’ offices.
In a single-blind challenge, you will not know whether you are eating the challenge food or a placebo, which is a sample that does not include the challenge food. The health care professional giving the test will know. To help hide the challenge food, the taste is masked by adding it to another food. A single-blind challenge may be used if there is concern that anxiety could impact test results.
In a double-blind challenge, both you and the person giving the test do not know whether you are receiving the challenge food or a placebo. A second health care professional prepares the samples to keep track of which ones have the challenge food included. As the double-blind challenge is more time-consuming and labor-intensive, it is primarily used for research purposes.
After the test
You may be asked to stay in the doctor’s office for a period of one to four hours. The amount of observation time changes depending on if there was an allergic reaction and the severity of the symptoms.
After reviewing the results of your test, your doctor will discuss those results with you and tell you whether it is currently safe for you to eat the challenge food. If you do not have a reaction to a challenge food to which you were previously allergic, your health care provider may advise you about whether you can or should incorporate the challenge food into your diet. Do not start eating the challenge food without the approval of your doctor.
Oral Food Challenge Results
Receiving test results
The results of an oral food challenge are generally available immediately upon completion of the test. Your doctor will typically discuss the results of the test with you at the same appointment.
Interpreting test results
The results of an oral food challenge are reported as positive or negative for an allergy.
If the consumption of the challenge food does not cause an immune reaction, the test is considered negative, and it is unlikely that you have an allergy to that food. If it does produce a reaction, then the test is considered positive.
An oral food challenge alone cannot diagnose a food allergy. The results must be consistent with your medical history. Your doctor will go over the results of your test with you and provide guidance regarding the challenge food.
Are test results accurate?
The results of an oral food challenge are generally accurate, though no test is perfect.
The main factor that must be accounted for when considering the results of the test is bias. In most oral food challenges, the patient knows that they are eating the challenge food, so there is a risk that some reactions could be caused by anxiety rather than an immune response.
If there is reason to believe that anxiety played a role in a reaction during an oral food challenge, the test may be repeated as a single-blind test where the person being tested does not know if they are eating the challenge food or a placebo.
Additionally, because the oral food challenge uses samples that may not be prepared in the same way as in the real world, an oral food challenge cannot accurately measure the severity of a food allergy. It can only diagnose whether there is an allergy or not.
Do I need follow-up tests?
As oral food challenges are primarily used to confirm an allergy, most people do not need follow-up tests. There are two circumstances when follow-ups may be used:
- If you have a negative result from an oral food challenge, your doctor may want you to eat a full portion of the challenge food prepared in a typical fashion.
- If your doctor believes your allergy has improved or resolved, they may repeat an oral food challenge.
Questions for your doctor about test results
Your doctor will likely provide you with an opportunity to ask questions after your test. These are some suggestions for questions that may be helpful:
- What was the result of my oral food challenge?
- Do I need any follow-up tests?
- Should I have another oral food challenge in the future for the same food?
- Should I be tested for any other foods?
Oral food challenge vs. other allergy testing
Although an oral food challenge is one of the only tests that can confirm a food allergy, there are other tests that can be used prior to an oral food challenge to help determine what food is triggering the allergy and if an oral food challenge is necessary. These are an allergy blood test, an allergy skin test, and a food elimination test.
An allergy blood test involves a small blood sample taken with a needle, which is then examined for substances and cells that indicate whether an allergy is likely.
In an allergy skin test, small amounts of the suspected allergen are injected under the skin, which is then checked for a reaction such as an itchy, red bump.
In a food elimination test, you stop eating all suspected foods and then add each back to your diet one at a time to see which produces a reaction.
