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.