What information is gained from food patch testing?
Food patch testing is used to detect possible food allergies. This test differs from ImmunoCap blood tests or skin prick tests, which are used to evaluate for immediate reactions that may result in symptoms such as hives or anaphylaxis (severe allergy reaction).
In contrast, patch tests are used to evaluate delayed-type reactions. Combining these two types of testing may better identify foods that are causing disease symptoms.
Who may benefit from food patch testing?
Patch testing may be useful for patients with diseases such as eosinophilic esophagitis or atopic dermatitis that may be caused, in part, by underlying food allergies.
Foods identified by blood or skin prick testing may or may not overlap with foods identified by patch testing. At this time, it is still unclear what the performance of either test is for evaluating delayed-type reactions, however, we and other experts suspect that they may be useful for identifying allergens in some patients.
How is food patch testing performed?
Food patch testing, in most situations, will require three separate visits to the Food Allergy Center:
- Visit 1: During the initial visit, food patch test panel(s) will be placed on the back of you/your child. These panels consist of prepared food extracts placed on shallow aluminum disks, which are taped to the skin. These panels must remain intact for 48 hours. This requires that they do not get wet or shift their location on the back. The selection of foods for testing will be determined by your allergist. In general, foods that are positive by blood or skin prick testing will NOT be included for patch testing.
- Visit 2: 48 hours after patch placement, the patient will return to the clinic for patch removal and evaluation by a nurse.
- Visit 3: 72 hours after patch placement, the patient meets with the physician for evaluation and interpretation of patch testing results.
What are the possible side effects of food patch testing?
Patch tests are well tolerated by most patients. The most common side effect is some redness and/or irritation caused by the tape, which generally disappears in one or two days after removal of patches. Rarely, patients may experience burning, itching and/or discomfort due to a reaction to a test food.
What preparation is required for patch testing?
- 1 month before: Stop any oral steroids or systemic immunosuppressants. (Check with doctor before doing this.)
- 7 days before: Do not apply topical medications like Protopic, Elidel or steroids to test site area.
- 2 days before: Do not apply any moisturizers to skin on back.
- Continue as usual: Antihistamines (e.g., Claritin, Zyrtec, Allegra, Benadryl), inhaled steroids (e.g. Flovent, Pulmicort, Advair, Symbicort), Singulair and swallowed inhaled steroids (e.g., Flovent, Pulmicort).