Skin Prick Testing (SPT) is the preferred method for evaluating patients with food allergies. This can be done in children as young as a few months of age. Extracts containing the suspected food allergen are placed on the skin of the forearm in a prick or scratch method using a device similar to a plastic toothpick. The site is then monitored for the development of redness and swelling at the site of administration over the next 10-20 minutes. We encourage you to bring books, toys or other items to distract your child during the test. The food allergen is then removed and Benadryl liquid is applied to the site. A positive SPT indicates a possible association between the food being tested and a patient’s reaction to the suspected food. The reliability of a positive SPT is only about 50% in general; however in cases of anaphylaxis it can confirm the diagnosis. A negative SPT is about 95% predictive but may be a false negative in the very young. This is the situation when the RAST test can be utilized.

RAST Testing is a blood test whereby a patient’s IgE, the allergy antibody, is measured against a specific food. This is considered less reliable than the SPT because there is a higher false positive rate than the SPT. A negative test has the same utility as the SPT. This study is sent to a laboratory therefore the results are not immediately available as they are with the SPT. This test is generally used when there are other factors that preclude the use of the SPT such as severe atopic dermatitis (eczema) with limited clear skin for testing, patients that cannot discontinue antihistamines or the rare patient that is so sensitive that SPT may have inherent risk. RAST tests can be monitored over time. If the value decreases to an acceptable level, a food challenge can be performed under physician supervision in the office.