A blood test or skin prick test isn't enough to diagnose a food allergy according to experts. Here's what all parents should know.
There's no doubt that food allergies are a worrisome issue. They seem to be on the rise among children, though no one understands quite why. But according to a new report summarized in the journal Pediatrics, overdiagnosis of food allergies may be a problem too.
Many foods can cause allergic reaction, but milk, eggs, peanuts, tree nuts, and seafood are responsible for the most serious cases. In a study that relied on parent reports, as many as eight percent of children may have food allergies.
But according to the paper, self-reports tend to overestimate actual allergy. For instance, in one study, rates of self-reported food allergy were 12 percent—but that dropped to just three percent when more tests were conducted to confirm it. In another study, kids who were avoiding a certain food because of suspected allergies were given that same food in an oral food challenge (that's when a small amount is fed to the patient under medical supervision). Turns out, more than 90 percent of them were actually able to tolerate it.
Overdiagnosis of food allergy may be the result of overtesting and misunderstanding the results. It's a common misconception that a positive result from a blood test or skin prick test always means there's an allergy to the food. As the authors explain, these tests only detect antibodies to the food, but they don't diagnose an allergy on their own. Case in point: About eight percent of the population will have a positive allergy test to peanut, but most are not actually allergic, says Scott Sicherer, M.D., a professor of Pediatrics at the Icahn School of Medicine at Mount Sinai in New York City, author of Food Allergies: A Complete Guide to Eating When Your Life Depends on It, and one of the paper's authors. Yet in a survey of more than 400 primary care doctors, nearly 40 percent said that blood tests and skin prick tests were enough to make a diagnosis.
Though it's appropriate to start the conversation about food allergies with a general physician, the recommendation is to see someone who has experience and training in allergies, such as an allergist-immunologist, for a complete evaluation. "No simple test provides a diagnosis," says Dr. Sicherer. "Diagnosis can be complicated and is often a time-consuming process."
Diagnosis should involve evaluating family history as well as the patient's own history with the food—then using further tests and tools such as blood tests, skin prick tests, and elimination diets to help verify it. "For instance, if a child ate peanuts for the first time and developed immediate hives, swelling, and trouble breathing, a positive allergy test such as a blood test could confirm the allergy," explains Dr. Sicherer.
An oral food challenge (when also done using a placebo) is considered the best way to diagnose a food allergy. Dr. Sicherer says that may be recommended when history and test results aren't giving enough info for a diagnosis and the family wants to see if the food can be tolerated. It might also be used to check whether an allergy has been outgrown.
A red flag of possible food allergy is a reaction within minutes to hours of eating the food, especially when it happens more than once. Food allergies are also a common culprit behind moderate to severe eczema in babies and children. But food allergies do not cause chronic asthma or hay fever-type symptoms in children.
Besides putting unnecessary stress on families, misdiagnosis of a food allergy means a child will be avoiding foods she doesn't need to avoid—and that can needlessly eliminate important nutrients, especially when multiple foods are cut out of the diet. "Avoidance of foods affects nutrition and quality of life," says Dr. Sicherer. "It's important to get it right."
Sally Kuzemchak, MS, RD, is a registered dietitian, educator, and mom of two who blogs at Real Mom Nutrition. She is the author of The Snacktivist's Handbook: How to Change the Junk Food Snack Culture at School, in Sports, and at Camp—and Raise Healthier Snackers at Home. She also collaborated with Cooking Light on Dinnertime Survival Guide, a cookbook for busy families. You can follow her on Facebook Twitter Pinterest, and Instagram. In her spare time, she loads and unloads the dishwasher. Then loads it again.