When testing for food allergies, allergists often ask about family history. If your parents have food allergies, the chances are higher that you too will have them. Problem is, not everyone who reports a food allergy actually has one.
A study in Annals of Allergy, Asthma and Immunology, the scientific publication of the American College of Allergy, Asthma and Immunology (ACAAI) reports only 28 percent of parents of kids with food allergies tested positive to the foods to which they reported allergies. A sensitivity to a food can be indicated in a skin prick test or a blood test, but does not always show a true allergy unless there has been a previous reaction to the food.
"Parents of kids with food allergies had a higher rate of positive blood and skin tests to foods than the general population," said allergist Melanie Makhija, MD, MSc, ACAAI member and co-lead author. "But of the 2,477 parents, only 28 percent of those who self-reported a food allergy actually tested positive. This tells us that either people haven't been tested and are assuming an allergy from a previous reaction to a food, or they haven't been tested properly and may not truly have an allergy. Allergy testing, including blood and skin prick testing, is not always reliable; there are a lot of false positives."
Parents of children with food allergies were recruited from local hospital clinics and community settings. To be eligible, families had to have a child with a food allergy. In response to the questionnaire, 13.7 percent of parents reported having a food allergy. Of that group, only 28 percent tested positive to the food to which they reported being allergic.
"Previous studies have focused on the general adult population," said allergist Rachel Robison, MD, study co-lead author. "While we found positive test results were more common in parents of kids with food allergies, the actual levels in the blood for the foods were quite low. Low positives in allergy testing are more likely to be false positives This points to the importance of proper testing for any kind of allergy, but particularly food allergies. Interestingly, we also found that of the parents who reported no food allergy, 14 percent had positive tests to peanut and sesame, for example."
According to ACAAI, skin tests may reveal sensitization, but being sensitized to an allergen doesn't mean you are allergic. Oral food challenges remain the gold standard for allergy testing and are considered very accurate for diagnosing allergies. An allergy blood test alone is not as accurate. Food allergy tests aren't able to predict future risk for someone who has never eaten the food before.