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.