Sometimes, even after performing skin prick and blood tests, an allergist is unable to arrive at a definitive diagnosis. In this case, you may be asked to undergo an oral food challenge (OFC), a highly accurate diagnostic test for food allergy. Because this test has the potential to cause a serious reaction, it should only be performed by an experienced allergist at a medical facility where the appropriate medications and equipment are available. Extensive studies have shown that OFCs are very safe when administered in this way, and the medical community has developed comprehensive guidelines and standards for these tests. Indeed, many thousands of OFCs have been performed worldwide with an excellent safety record.
During the food challenge, the allergist feeds you the suspect food in measured doses, starting with very small amounts that are unlikely to trigger symptoms. Following each dose, you are observed for a period of time for any signs of a reaction. If there are no symptoms, you will gradually receive increasingly larger doses. If you show any signs of a reaction, the food challenge will be stopped. With this regimen, most reactions are mild, such as flushing or hives, and severe reactions are uncommon. If necessary, you will be given medications, most often antihistamines, to relieve the symptoms.
If you have no symptoms, food allergy can be ruled out. If the test confirms that you do have a food allergy, your allergist will discuss food avoidance techniques and prescribe appropriate medications.
In some cases, OFCs are administered to people who already have been diagnosed. An allergist may order the test to find out if a patient has outgrown a food allergy. In clinical trials, OFCs help researchers learn how well participants are responding to the treatment under study.
THERE ARE THREE KINDS OF ORAL FOOD CHALLENGES:
Double-Blind, Placebo-Controlled Food Challenge (DBPCFC)
This test is considered the “gold standard” for diagnosing a food allergy. The patient receives increasing doses of the suspected food allergen or a placebo (a harmless substance). Since the allergen and the placebo look alike, neither you nor your doctor will know which one you are receiving – hence the term “double-blind.” For example, if you are being tested for milk allergy, you may eat a piece of hamburger that contains milk powder, or a look-alike that has no milk in it. This process ensures that the test results are objective. Neither the patient’s anxiety nor the allergist’s preconceptions can influence the outcome.
Single-Blind Food Challenge
In this test, the allergist knows if you’re receiving the allergen, but you don’t.
Both you and your doctor know whether or not you’re receiving an allergen. This type of challenge is most often done when a patient’s nervousness is unlikely to affect the results.