Are tree nut allergies
diagnosed too often?
American College of
Allergy, Asthma, and Immunology
Many patients with a
history of a single tree nut allergy are told to avoid all other tree nuts. But
is that necessary?
If you have a tree nut allergy and were advised to avoid
other tree nuts based only on a positive blood or skin prick test, you may not
be allergic to the other nuts.
New research strongly suggests you should
consider having an oral food challenge to properly diagnose additional nut
allergies, especially if you've never had a reaction to eating those tree nuts
before.
A new study in Annals
of Allergy, Asthma and Immunology, the scientific publication of the
American College of Allergy, Asthma and Immunology (ACAAI) showed that among
people allergic to one nut who have a positive test to other tree nuts, more
than half passed an oral food challenge to other tree nuts without a reaction.
Passing an oral food challenge means you aren't allergic to that nut.
Tree nuts
include almonds, cashews, walnuts and hazelnuts, but not peanuts.
The study noted that nearly none of the people allergic to peanut, but sensitized to tree nut, were clinically allergic to tree nut. This is the first study indicating that peanut allergic people may not need to avoid all nuts.
"Too often,
people are told they're allergic to tree nuts based on a blood or skin prick
test," says allergist Christopher Couch, MD, ACAAI member and lead author
of the study.
"They take the results at face value and stop eating all
tree nuts when they might not actually be allergic. We examined records of 109
people with a known tree nut allergy to an individual nut. They were tested for
other tree nuts they had never eaten before using blood or skin prick tests.
Despite showing a sensitivity to the additional tree nuts, more than 50 percent
of those tested had no reaction in an oral food challenge."
An oral food challenge
is considered the most accurate way to diagnose food allergy. During an oral
food challenge, the patient eats tiny amounts of the food in increasing doses
over a period of time, followed by a few hours of observation to see if they
have a reaction.
An oral food challenge should only be conducted under the care
of a trained, board-certified allergist. You should never do one on your own
since if you are allergic, you could have a severe, life-threatening reaction.
"Previous studies
suggested people with a tree nut allergy, as well as those with a peanut
allergy, were at risk of being allergic to multiple tree nuts," said
allergist Matthew Greenhawt, MD, chair of the ACAAI Food Allergy Committee and
study co-author.
"We found even a large-sized skin test or elevated blood
allergy test is not enough by itself to accurately diagnose a tree nut allergy
if the person has never eaten that nut. Tree nut allergy should only be
diagnosed if there is both a positive test and a history of developing symptoms
after eating that tree nut."
Dr. Greenhawt stressed
the study did not include challenges to nuts the individual had a documented
history of having a reaction to when eaten.
"The practice of avoiding all
peanut and tree nuts because of a single-nut allergy may not be
necessary," says Dr. Greenhawt. "After an oral food challenge, people
allergic to a single tree nut may be able to include other nuts in their
diet."