Author: V. Dimov, M.D., Allergist/Immunologist and Assistant Professor at University of Chicago
The only definitive test to rule out food allergy is an oral food challenge performed by a board-certified allergist in a specialty clinic. The skin test and the blood test (sIgE) can point to the likelihood of a successful food challenge but they do not make the diagnosis. It is important to note that in 10–25% of food allergy reactions, sIgE can be undetectable by blood test (http://buff.ly/1e7HAmY).
8 foods cause 90% of food allergies (click to enlarge the image). The likelihood of a negative oral food challenge is shown in relation to the respective values of skin prick test (SPT) and serum IgE (sIgE):
There is a high false positive rate with blood test or skin test for food allergy. For example, a child or an adult can get a positive test, but at the same time they can eat that food and nothing happens. A negative skin test is more accurate. If the skin test is negative, you almost certainly are not allergic to the food. If the skin test or the blood test is positive, there is only about 50% likelihood that you are allergic, in most cases.
In one recent study, 89% of oral food challenges performed with foods being avoided at baseline were negative. 84-93% of the foods being avoided were returned to the diet after an oral food challenge, indicating that the vast majority of foods that had been restricted could be tolerated.
Unless children show very high reactions on skin test or blood test, an allergist can administer food challenges to find out if they are truly allergic. The blood and skin tests also cannot predict whether children would have a mild or severe reaction to certain foods. A board-certified allergist will help you decide what foods are safe so that you can expand you or your child's food with health and nutritional foods.
Read more about oral food challenges here:
Food Challenges for Diagnosis of Food Allergy
Food allergies challenge families - allergy doctors offer solutions