Food Allergy Skin Testing
Food allergy testing is a very sensitive form of skin 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 in which to diagnose food allergies. Allergy skin tests can identify allergic antibodies to foods that can cause an allergic reaction.
After first cleansing the patient’s back with alcohol, the nurse will use a pen to label the area where the food allergen will be applied. The nurse will then prick the skin with an applicator containing a specific food allergen to which the patient may be allergic.
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, the patient consumes small amounts of food in increasing dosages. The patient may be monitored here in our office for several hours.
Alternatives to Skin Testing
An alternative to skin testing is specific IgE blood testing (RAST/Immunocap), 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.
Medications & Allergy Testing
The following medications may interfere with allergy testing and should be discontinued prior to the test procedure:
- Antihistamines. Patients should not use many over-the-counter antihistamines, cold medications, sleeping aids and allergy such as Benadryl (diphenhydramine), Chlor-Trimeton (chlorpheniramine), Tavist (clemastine), Robitussin Night Time andTylenol PM at least three days prior to the testing. Additionally, patients should not use over-the-counter Claritin or Alavert (loratadine), Allegra (fexofenadine) along with Zyrtec (cetirizine) one week prior to skin testing. Prescription antihistamines, such as Xyzal (levocetirizine) and Clarinex should also be stopped seven days prior to the skin testing. Astelin, Astepro and Patanase nasal spray should be stopped five to seven days prior to testing, but intranasal steroids may be continued.
- Beta-blockers. Patients should not use beta-blockers when testing is planned. These drugs must not be discontinued without physician guidance, so it is extremely important to consult the allergist to design a discontinuation program if skin testing is required.
- Antidepressants. Patients should discontinue the use of some antidepressants such as amitriptyline one week prior to skin testing. However, some of the newer antidepressant-type medications do not interfere. Please contact the office with the names of your medications to find out which antidepressants might interfere with allergy testing.
Please call the office for any questions on medications.