An Overreaction to Food Allergies
Many children are wrongly diagnosed with food
allergies because of inaccurate tests
By EHealth »
Scientific American Volume 313,
» The Science of Health
llen Ruppel Shell | Oct
few years ago a 15-month-old girl—her stomach, arms and legs swollen and her
hands and feet crusted in weeping, yellow scales—was rushed to the emergency
room at the University of Texas Southwestern Medical Center in Dallas.
Laboratory tests indicated a host of nutrition problems.
child's mother, during the previous year, had told doctors that standard infant
formula seemed to provoke vomiting and a rash. The mother and her pediatrician
assumed the girl was allergic to the formula and switched her to goat's milk.
Symptoms persisted, though, and the baby was switched again, to coconut milk
and rice syrup. At 13 months, the pediatrician noted yet another red, swollen
rash and ordered an allergy test, the child's first. The test identified
coconut as a so-called high-reaction class, and coconut milk was removed from
her diet. Reduced to a diet of rice milk, the child's symptoms worsened.
ER, doctors determined the girl suffered from kwashiorkor, a nutritional
disorder rarely seen in the developed world. She was fed intravenously and
evaluated by a team that included pediatric allergist J. Andrew Bird, who used
more sophisticated methods to test her response to coconut and cow's milk,
wheat, soy, egg white, fish, shrimp, green beans and potatoes. To her mother's
astonishment, the toddler showed no adverse reaction to any of them. After a
few days of steady nourishment and a course of antibiotics to clear her skin of
various infections, she was released from the hospital into a life free of food
restrictions. (Her digestive upsets appeared to be caused by a variety of
common ailments that would have almost certainly cleared on their own.)
problem was not in the baby but in the tests. Common skin-prick tests, in which
a person is scratched by a needle coated with proteins from a suspect food,
produce signs of irritation 50 to 60 percent of the time even when the person
is not actually allergic. “When you apply the wrong test, as was the case here,
you end up with false positives,” says Bird, who co-authored a paper describing
the Dallas case in 2013 in the journal Pediatrics. And
you end up with a lot of people scared to eat foods that would do them no harm.
Bird has said that he and a team of researchers found that 112 of 126 children
who were diagnosed with multiple food allergies tolerated at least one of the
foods they were cautioned might kill them.
Nadeau, director of the Sean N. Parker Center for Allergy Research at Stanford
University, says that many pediatricians and family physicians are not aware of
these testing flaws. “When it comes to diagnosis, we've been in the same place
for about 20 years,” she observes. To move forward, Nadeau and other
researchers are developing more advanced and easily used methods.
allergies are real and can be deadly, but mistakenly slapping an allergy label
on a patient can be a big problem as well. First, it does not solve the person's
troubles. Second, a diagnosis of allergies comes with a high price: a few years
ago Ruchi S. Gupta, a pediatric allergist affiliated with the Northwestern
University Feinberg School of Medicine, estimated the annual cost of food
allergy at nearly $25 billion, or roughly $4,184 per child, with some of that
attributed to medical costs but even more to a decline in parents' work
is a mental health price as well: children who believe they have a food allergy
tend to report higher levels of stress and anxiety, as do their parents. Every
sleepover, picnic and airplane ride comes fraught with worry that one's child
is just a peanut away from an emergency room visit or worse. Parents and
children must be ever armed with an injectable medicine that can stave off a
severe allergic reaction. The prospect of a lifetime of this vigilance can
weigh heavily on parents, some of whom go so far as to buy peanut-sniffing dogs
or to homeschool their children to protect them both from exposure to the offending
food and from the stigmatization of the allergy itself.
allergist John Lee, director of the Food Allergy Program at Boston Children's
Hospital, has heard more than his share of horror stories. “Food allergies can
be terribly isolating for a kid,” he says. “One parent told me his child was
forced to sit all alone on a stage during lunch period. And siblings can feel
resentful because in many cases parents don't feel they can take family
vacations or even eat dinner in a restaurant.”
a food allergy usually begins with a patient history and the skin-prick test.
If the scratch does not provoke a raised bump surrounded by a circle of red
itchiness, the patient almost certainly is not allergic to the material. But
positive tests can be harder to interpret because skin irritation does not
necessarily reflect a true allergy, which is a hypersensitivity of the immune
system that extends through the body. In a real allergy, immune components such
as IgE antibodies in the blood are stimulated by an allergen. The antibody
binds to immune cells called mast cells, which then triggers release of a
cascade of chemicals that produce all kinds of inflammation and irritation. But
levels of allergen-specific antibodies in the blood are quite low even in
allergic people, so running a simple blood test is not an answer, either.
diagnostic “gold standard” for food allergy is a placebo-controlled test. A
potential irritant is eaten, and the body's response (a rash, say, or swelling)
is compared with what happens after eating something that looks like the
irritant but is benign. For example, a patient who might be allergic to eggs is
given a tiny amount of egg baked into a cake, along with a taste of egg-free
cake. Ideally, the test is double-blind, meaning that neither the patient nor
the allergist knows which cake contains egg. The accuracy rate of these tests,
for both positive and negative results, is about 95 percent, according to Lee.
this procedure is tricky, time-consuming, expensive and relatively uncommon;
experts agree that few allergy sufferers have access to it.
Baker, who is a physician and immunologist and CEO of the nonprofit Food Allergy
Research & Education (FARE), says his organization is tackling this problem
by setting up 40 centers around the country to administer food challenges with
all the necessary precautions. “You have to be prepared to treat or transport
people to the emergency room if they react,” he asserts.
are also looking for something easier to use. One promising newcomer to the
diagnostic arsenal is the basophil-activation test (BAT). Basophils, a type of
white blood cell, excrete histamines and other inflammatory chemicals in
reaction to a perceived threat—such as an allergen. Nadeau and her colleagues
have designed and patented a test that involves mixing just one drop of blood
with the potential allergen and measuring the reaction in basophils. In pilot
studies, the procedure diagnosed allergies with 95 percent accuracy in both
children and adults, a rate similar to that of food-challenge tests.
still in the research phase and requires more studies with a larger, more
varied population, but another approach—allergen-component testing—has already
been approved by the U.S. Food and Drug Administration for peanut allergies.
Lynda Schneider, a pediatric allergist and director of the Allergy Program at
Boston Children's Hospital, says that some children have a mild sensitivity—but
not a full-blown allergy—to one protein in peanuts. Rather than testing them
with crude mixtures of lots of proteins found in nuts, Schneider's component
tests isolate specific proteins and then challenge the patient with those. By
sorting out which protein is prompting the negative reaction, physicians can
determine with a high degree of accuracy whether the patient is truly allergic
wants to get beyond diagnosis and into treatment. Omalizumab is a monoclonal
antibody that binds to IgE antibodies and prevents them from glomming on to
mast cells, which triggers the allergic cascade. In a recent study, Schneider
and her colleagues administered this so-called anti-IgE drug over the course of
20 weeks to 13 children who were known to have peanut allergies while giving
them a gradually larger dose of peanuts. During the anti-IgE phase, none of the
children developed an allergic reaction to peanuts, although two did have a
recurrence once the anti-IgE regime ended. “The anti-IgE allowed their system
to go through a desensitization process,” Schneider says.
who are allergic to milk and eggs can be gradually desensitized by heating
these foods for 30 minutes or so, Bird has found. The heat changes the shape of
these proteins, which vastly reduces their tendency to provoke allergies. This
is not a home remedy, and it is done under medical supervision, but studies of
kids who are fed small amounts of heated egg or milk show the children are far
more likely to acquire a tolerance to these foods over time—that is, more
likely to outgrow the allergy. A study called Learning Early About Peanut
Allergy (LEAP) showed that exposing children to tiny amounts of peanut products
early in their life dramatically reduced the incidence of allergy.
H. Sicherer, a professor of pediatrics, allergy and immunology at the Icahn
School of Medicine at Mount Sinai, takes the early desensitization idea a step
further. He suggests children can best avoid food allergies if they eat a wide
variety of foods at an early age, run in the open air and “play in the dirt.” A
little less protection from the world, he says, may be the best protection from
ABOUT THE AUTHOR(S)
Ellen Ruppel Shell is
author, most recently, of Cheap:
The High Cost of Discount Culture and is co-director
of the Graduate Program in Science Journalism at Boston University.