A food challenge test is a highly accurate method of determining the cause of a food allergy. The test uses capsules of various foods, some of which are suspected of causing an allergic reaction, which are taken like a pill by the patient. A period of observation after each dose allows a physician to monitor whether or not an allergic reaction takes place as a result of consuming that allergen.

Because a food challenge test involves provoking an allergic reaction, there is some risk associated with it. A food allergy reaction can be fatal if not immediately treated. The test should always take place at a site that is well-equipped to deal with any sort of reaction the individual may have. Food challenges should never be performed at home. Individuals who are susceptible to anaphylactic shock should participate in a food challenge test only if a physician determines that the test is absolutely necessary.

The test is performed without either the patient or the physician aware of which capsules contain the suspected problem foods. This eliminates the psychological effect of an expected response. If no allergic reaction takes place, the results suggest no allergy to that food type. This is then conclusively determined with an open challenge, which is the consumption of a regular portion of the food in question.

Before participating in a food challenge test, individuals will have to reduce the consumption of some medications, particularly antihistamines. Food should not be eaten several hours before the test takes place. A physician can offer specific guidance on what steps should be taken prior to the challenge.

Individuals who test positive for a food allergy will often retake the test to be sure the results are correct. If the results are substantiated with three positive test results, then complete removal of that food type from the diet is needed. A conclusive negative test result means that the food may be safely reintroduced to the diet.

Although highly accurate, food challenge tests can be time-consuming and expensive to perform, especially when multiple foods are being tested. For this reason, the test is usually performed to rule out a food allergy, so the physician can direct efforts at uncovering the true cause of a reaction.

The food challenge test is considered the most accurate way of determining whether a food allergy exists or to confirm that an individual is allergic to a specific type of food. For this test, varying amounts of a suspected food allergen are placed in capsules. A nonallergic substance is also placed in an equal amount of capsules to serve as a placebo. All the capsules look identical and neither the patient nor physician knows which capsule contains what substance. Known as a “double blind” format, this process allows for a greater degree of accuracy in the test results as it limits the possibility of a false-positive.

Patients take increasing doses of one type of capsule one at a time like a pill and are observed for signs of an allergic reaction. Then the second set of capsules is taken in the same manner. If a patient displays any signs or symptoms of an allergic reaction during the test, the testing is immediately halted and the patient is treated.

Usually a food challenge test can only be effectively administered once a physician and patient have used several other types of less accurate allergy tests to determine a short list of potential problem foods. These tests are capable of identifying foods as possible allergens, but their results are not always conclusive and can return false-positives. As a result, some physicians must use a food challenge test to conclusively rule out a food allergen. Tests that may be performed prior to food challenge testing include:

• RAST (radioallergosorbent test). Blood test that checks for antibodies that correspond to specific foods.
  
  
• Allergy skin test. Test that involves pricking, scratching or injecting food extracts into the patient’s skin to see if a reaction occurs.
  
  

  

By carefully controlling the conditions and dosages, a physician can determine if an allergic response occurs when a specific type of allergen is consumed, as well as how much of the allergen was needed to cause a response. The physician can also be sure the response was not subconsciously triggered by the patient, as neither the patient nor the physician knows which dose is the placebo and which is the allergen.

A positive test result indicates an allergic reaction to a food type did take place. However, it is not uncommon to generate a false-positive with this type of test. For this reason, many physicians suggest an individual repeat the test until three positive outcomes have been achieved.

If a test shows a negative result, the individual will undergo an open challenge, which involves eating a full-size portion of the food in question. This final portion of the test can conclusively demonstrate that a person is not allergic to a given food type. As with the rest of the test, this portion of the testing is conducted under the supervision of a physician who is equipped for treating anaphylaxis.

Because of the reactions involved, the test is not conducted on children younger than 3. It is also not recommended for patients with uncontrolled asthma.

There are several steps that should be taken before a food challenge test to prevent interferences that could affect the test results. It is important that individuals consult with a physician for specific preparation instructions, which generally include:

• In the seven- to 14-day period before the test, eliminate all foods that are suspected allergy triggers from the diet. This helps ensure that any allergic response that takes place during the test is caused by one of the test challenges, and not earlier allergen contact.
  
  
• Do not consume anything more than water in the two hours prior to the test (a physician may recommend a longer fasting period in some adults). It is best to administer the test to a person with an empty stomach. This further ensures that any allergic reactions experienced during the test were the direct result of a food challenge.
  
  
• Discontinue the use of antihistamines for three to seven days before the test and minimize the amount of other medications taken. A physician will be able to safely schedule these medication changes. Though many types of antihistamines and other medications are effective at blocking or reducing allergic reactions, this works against accurate test results. For the test, the individual needs to be as sensitive to the allergens as is safely possible.
  
  
• Individuals should not have taken a food challenge test for a different food type within three to five days of the test.

The food challenge test can be a lengthy procedure that requires the whole day. Though any sort of allergic reaction that occurs during the testing will be immediately treated in a clinical setting, it might be a good idea for patients to have someone available to drive them home in case symptoms persist.

The food challenge test is usually administered either at a physician’s office or hospital on an outpatient basis. A patient should never attempt a food challenge at home. The testing should only be conducted where there is adequate personnel and equipment for dealing with anaphylaxis. Sensitive patients who are at a higher risk for anaphylactic shock should not participate in a food challenge test unless a physician determines it is absolutely necessary.

Physicians recommend that highly-allergic individuals who have severe allergic reactions be connected to an intravenous (IV) injection during their food challenge test. This allows the person to receive medication very quickly in the event of a strong reaction. However, this step is not necessary for most people taking the test. Should any sort of allergic reaction occur during the test, the testing will immediately stop and the patient will receive treatment to relieve symptoms.

Food challenge testing is a lengthy procedure that can last for many hours or even take several days (though the patient can go home at night). The test will begin with the patient swallowing a capsulated dose of food. This dose will be either a placebo (inactive substance that does not cause any effects) or a small amount of the suspected food allergen. After consuming the opaque capsule, the patient and physician (usually a board-certified allergist) will wait between 30 minutes and two hours to see if an allergic reaction occurs. If a reaction occurs at any time during the challenge, the testing is immediately stopped.

As this is a blind test, neither the physician nor the patient will know whether the dose being taken is the allergen or the placebo. Another medical professional will make up the capsules, and a disinterested third party (often a dietitian) will keep track of that information until after the test is complete.

Over the next hour or so, increased doses of the same substance (placebo or allergen) will be administered to the patient in capsules. A period of observation (usually about 30 minutes) will take place after each. Once the patient has tolerated a complete dose (equal to a normal meal-size portion) without any allergy symptoms, an allergic reaction to that substance can be ruled out. At this point a second series of doses is taken with the remaining placebo or allergen. These are administered just like the first, until that substance, too, causes a response or is ruled out.

Many physicians will administer one dose in the morning and the second around lunchtime to provide for adequate observation time. Because of these long observation times, a single test can take an entire day.

An equal number of placebos and food allergen challenges will always be given. This means that to test for two suspected types of food allergy, four series of doses need to be administered (two placebos and one of each of the allergens). Some versions of this test will use several types of the same allergen along with several placebos to increase test accuracy and limit false positives. With the potential for many different doses and an observation period needed in between each dose, this type of testing can take days when testing for several types of allergen.

An individual will need to remain under medical observation for a short period of time following the food challenge test to ensure that no allergic reactions take place. Physicians will consider a number of factors, including the timing and severity of the patient’s previous reactions, when deciding on an appropriate amount of time for observation following the completion of a food challenge test. Once the physician is convinced that a reaction will not occur as a result of the food challenges, the patient will usually be allowed to go home. It is a good idea that patients have someone to drive them home in case a strong allergic reaction occurs during testing.

Once at home, an individual may occasionally have a late-phase allergic reaction to the earlier testing. This type of reaction can occur several hours after exposure to an allergen occurs. Having this type of late-phase reaction would indicate a positive test response to an allergen – provided nothing had been eaten since the challenge testing.

If a person has no reaction to the food challenge, the physician will often bring the patient back in to confirm the negative results with an open challenge. This type of test involves the patient knowingly consuming a normal serving of the previously suspected food while under a physician’s observation. This challenge will conclusively determine whether a given food can be safely eaten. After successfully passing an open challenge, patients are often directed to reintroduce the food in question to their normal diet, as desired.

If a patient tests positive for a food allergy, follow-up visits with the physician are usually scheduled to discuss removing the problem food from the patient’s diet. Because exposure to a food allergen can be dangerous or even deadly, it is very important that people continually avoid any foods to which they are allergic.

Food challenge tests are, by design, intended to provoke an allergic reaction in individuals who have a food allergy. For this reason, there is a certain degree of risk involved with the testing. Physicians work to reduce this risk by conducting the test in a controlled environment that has adequate medical facilities present. Physicians also use challenge doses that build gradually to provoke the mildest type of allergic reaction possible for each individual. Any patient who has an allergic reaction during the test will be immediately treated.

Unfortunately, some people are severely allergic to even trace amounts of an allergen. These individuals can react strongly to even the most diluted dose of an allergen taken during a food challenge. Individuals who are prone to the life-threatening reaction known as anaphylactic shock should participate in food challenge testing only if a physician determines it is absolutely necessary. Physicians recommend that highly sensitive individuals take the food challenge test while connected to an intravenous (IV) injection so that medications may be quickly administered in the event of a reaction.

Individuals that have a negative result from just one food challenge and open challenge (which confirms the results of the food challenge) are generally able to normally eat those substances to which they test negative. Once a physician has reviewed the test results and determined they are negative, an individual does not need to seek any further treatment for that type of food allergy. If other types of allergens are still suspected, those can be tested by other food challenge tests

A food allergy can result in a deadly reaction if not treated properly. For individuals who positively identify a type of food allergy, avoidance is the key. The only effective type of treatment for people with a food allergy is the complete removal of problem foods from the diet. This is oftentimes a difficult and disruptive practice, but it can completely prevent reactions to a food allergen when diligently observed.

Completely avoiding a certain food type involves education and attentiveness. Food allergic individuals need to learn the different names, forms and extracts of the food they are allergic to. They should conscientiously check the ingredient labels on foods, educate themselves about dangerous cooking techniques and be particularly careful when dining outside the home.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to the food challenge test:

1. Why are you recommending that I undergo a food challenge test?
   
   
2. How long will the test take? Where will I have to go for the test?
   
   
3. How should I prepare for the test?
   
   
4. What risks do I face by undergoing this test?
   
   
5. What will happen if I have a reaction during the test?
   
   
6. What if I have a reaction after the test when I am at home?
   
   
7. Will I have to take the test more than once?
   
   
8. Can I perform a food allergy test on my own?
   
   
9. What will be the next step if my results are positive?
   
   
10. How accurate is this test? Can I trust the results?