Drs. Michael and Adrianne Vaughn
115 Gallery Circle
San Antonio, TX 78258
(Stone Oak MRI/Urgent Care Bldg.)
Food Allergy Challenge Testing
Foods can cause many different types of allergic symptoms. Some persons experience gastrointestinal problems such as cramping, constipation or diarrhea. Other persons suffer from skin rashes (hives or eczema). Less commonly, some may experience serious life-threatening reactions such as: asthma, throat closing or loss of consciousness. A food that causes allergic symptoms usually causes similar symptoms on each repeated exposure, provided that the same amount of food is eaten each time (rarely symptoms can be more severe). Some persons are allergic only to raw foods while others are allergic only to cooked foods. (Most persons will react to both). Very small amounts of foods may trigger allergic reactions and as a result, are often difficult to identify.
Food allergy symptoms can be immediate; usually beginning within 2 hrs. of ingestion, or delayed; in which symptoms which may not develop for up to 72 hrs. "Immediate" food allergies are suspected when allergic antibodies (IgE) are detected in the blood by laboratory RAST testing or by skin prick testing. The presence of allergic antibodies to foods alone is usually not sufficient to diagnose a food allergy. The confirmation of food allergy often requires challenge testing. Challenge testing is performed only in situations in which a food is suspected of causing non-life threatening symptoms. If a food were strongly suspected of causing dizziness, throat swelling, (body tissue swelling) or shortness of breath, then challenge testing would not usually be recommended.
RAST testing reports the presence of allergic antibodies in the blood. Typically they are given numerical scores/classes (0 to 6). Class 0-1 is called "equivocal" and is rarely if ever significant. The higher the RAST class/score, the more likely it is that a true food allergy exists. Challenge testing should begin with the highest-RAST class foods and continue until all positive foods have been tested. Allergy symptoms that repeatedly develop after challenge testing with a food confirms sensitivity (allergy) and the lack of allergic symptoms usually disproves allergy. Not all RAST or skin test positive foods will cause allergy symptoms. Foods that are RAST or skin test negative rarely if ever cause immediate allergy symptoms. To be absolutely certain no allergy exists, challenge testing is occasionally recommended when skin testing and/or RAST testing is negative. (Challenge testing to RAST or skin test negative foods is usually not necessary).
Childhood eczema is the most common disease in which challenge testing is used to confirm food allergy. If eczema is the only allergic symptom thought to be triggered by foods, it is usually very safe to perform food challenge testing and this can be done at home. Challenge testing is often recommended when multiple foods are noted to have stimulated allergic antibodies to determine which of the foods are most likely to be causing the allergic symptoms. If serious allergic symptoms are possibly due to a food (but unlikely) (i.e. no allergic antibodies can be detected), challenge testing may occasionally be recommended, but this should be done only in a safer environment such as a hospital ER waiting room.
Again it must be stressed that if testing has detected allergic antibodies to a food and serious allergic symptoms are likely to have occurred following ingestion, avoidance is the only safe recommendation.
Before challenge testing is done, all suspected foods are usually eliminated from the diet for at least 2 weeks (or at least those foods with a RAST class 2 or greater score). Selecting only RAST test negative foods to eat is the "best" way to develop an elimination diet. Anti-histamine use should be stopped at least 5 days before challenge testing. Food challenges are done with only one food at a time. The food should be eaten slowly over a one hour time period and only water should be used as a drink. The largest amount of the food that is ever usually eaten should be consumed (i.e. a normal portion). No other foods should be given for 3 hours and no additional foods suspected of causing allergy (RAST positive foods) should be eaten for at least two days to observe for the development of any "delayed" allergic symptoms. If allergic symptoms develop at any time during the challenge test, the allergy medications contained in the key chain carrier that we have provided to you should be taken. The Epi-pen is used for severe life-threatening symptoms such as throat closing, severe cough (possible asthma), wheezing, shortness of breath or dizziness/passing out. If an Epi-pen is ever used you should call 911 immediately after.
If allergic symptoms are thought to occur following a challenge test, repeating this challenge on another day may be necessary to be certain it has caused the problem. In children, complete avoidance of any food proved to be causing allergic symptoms should continue for at least 2 years before re-exposure is attempted. Peanut, tree nuts, egg and seafood allergies are less likely to be ever "out-grown." Food allergies in adults do not typically ever "go away." If you do not understand challenge testing after reading this instruction sheet please call 499-0033 for further clarification before beginning. Never perform a challenge test on any food suspected of causing allergic reactions without a doctor's approval.
Drs. Michael & Adrianne Vaughn
Asthma & Allergy Associates