"We are living the impossible everyday," says a mom of two boys with multiple food allergies. "Food is everywhere. You have to be vigilant. It's a full-time job for me."
8 foods cause 90% of food allergies (TEMPS WFS) (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 very high false positive rate. You can get a positive test, but the person can eat that food and nothing happens. A negative test is more accurate. If the test is negative, you almost certainly are not allergic to the food, whereas if it's positive, there is really only about 50% likelihood you are allergic."
Unless children show very high reactions on blood and skin tests, doctors can administer food challenges to find out if they are truly allergic. The blood and skin tests also can't predict whether children would have a mild or severe reaction to certain foods.
It is important to note that in 10–25% of food allergy reactions, sIgE can be undetectable by blood test (http://buff.ly/1e7HAmY).
Oral Food Challenges (click to enlarge the diagram):
Food allergies challenge families. USA Today.