Food Skin Testing
Food allergy skin testing is a very sensitive form of food allergy testing and continues to be the benchmark used by most allergists. A large number of allergy cells or mast cells reside in the skin providing a very accessible area to diagnose food allergies. Allergy skin tests can identify allergic antibody to foods that can cause an allergic reaction. An alternative to skin testing is specific IgE blood testing (RAST) which has a lower sensitivity but it is very useful in patients with eczema or other skin disorders, in patients who have had severe food reactions, or if more detailed antibody evaluation is required in preparation for a food challenge.
The back is the area of the skin that is typically tested. It is first cleansed with alcohol and a pen is used to label the area in a grid-like pattern that indicates where the testing substance (food allergen) is to be applied. The skin is then pricked with a small, sterile, pointed instrument containing a specific substance (food allergen) to which the patient may be allergic. After a waiting period of about 15 minutes, the test is read. Positive reactions on skin testing are typically a red, itchy area with a raised center that may look like a mosquito bite. Skin testing on the back is compared with negative (saline) and positive (histamine) control tests to help gauge the intensity of the reaction.
Food challenges may be performed in our office when the doctor feels it would provide additional information. Using a graded-dose protocol under close observation, small amounts of the food are given in increasing dosages. The patient may be monitored here in our office for several hours.
The following medications may interfere with allergy testing and should be discontinued prior to the test procedure:
1. Antihistamines. Many over-the-counter antihistamines, cold medications and sleeping aids (Benadryl (diphenhydramine), Chlor-Trimeton (chlorpheniramine), Tavist (clemastine), Robitussin Night Time, Tylenol PM, etc.) should be stopped at least 3 days prior to the testing. Over-the-counter Claritin or Alavert (loratadine), Allegra (fexofenadine) along with Zyrtec (cetirizine) should be discontinued 1 week prior to skin testing. Prescription antihistamines, such as Xyzal (levocetirizine) and Clarinex should also be stopped 7 days prior to the skin testing. Astelin, Astepro and Patanase nasal spray should be stopped 5-7 days prior to testing, but intranasal steroids may be continued.
2. Beta-blockers. Beta-blockers should not be used when testing is planned. It is extremely important to consult the allergist to design a discontinuation program if skin testing is required as these drugs must not be discontinued without physician guidance.
3. Some antidepressants such as amitriptyline should be stopped 1 week prior to skin testing, but some of the newer antidepressant-type medications do not interfere. Please contact the office with the names of your medications to find out what to do.
4. Please call the office for any questions on medications.