Diagnosing a food
allergy is sometimes difficult and may involve a number of tests. This is
because food allergy symptoms may resemble those of a number of other
Symptoms may center
on a particular body area, such as the gastrointestinal system, so doctors have
to rule out other conditions that can cause similar symptoms.
If a food allergy
is suspected, your doctor will start by asking you to provide a detailed
history of your eating and dietary habits. They will also ask questions about
any past reactions you’ve had to certain foods.
According to the National
Institute of Allergy and Infectious Diseases (NIAID), your doctor may also
ask any of the following questions:
- Did your reaction come on quickly, usually within several
minutes after eating the food?
- Is your reaction always associated with a certain food?
- How much of this potentially allergenic food did you eat
before you had a reaction?
- Have you eaten this food before and had a reaction?
- Did anyone else who ate the same food get sick?
- Did you take allergy medicines, and if so, did they help? (For
example, antihistamines should relieve hives)
Your doctor may
also wish to perform a physical exam to rule
out other suspected medical conditions.
Food Diary and Elimination Diet
To identify the
culprit, your doctor may ask you to keep a food diary to record your eating
selections, symptoms, and any medications you may be taking.
They might then
advise you to avoid suspected foods for a couple of weeks and gradually add
them back one at a time. If your symptoms and reactions are severe, this
technique might not be safe.
A skin-prick test is one of the
primary tests used to diagnose a food allergy. For this test, a tiny bit of
each potentially problematic allergen (food protein) is inserted under the
skin. If the skin develops a bump or other noticeable change of appearance, you
are likely to be allergic to that particular protein. Results can usually be
seen in 15 to 30 minutes.
Some individuals test positive in the
skin-prick test for a certain food allergy without actually having this
allergy. Doctors will consider test results in conjunction with your symptoms
history in order to make a more conclusive diagnosis.
Your doctor may
want to order a blood test rather than a skin test, or they may order both.
A RAST test (short
for radioallergosorbent test) can measure your immune system’s response to an
allergen by detecting the amount of IgE antibodies made in response to
suspected food proteins.
In a RAST test, a
sample of blood is added to the suspected food protein and then tested for the
amount of antibodies made in response.
As with the
skin-prick test, a positive result does not always mean an individual has the
particular food allergy. Results will be considered along with the patient’s
history of reactions to the particular food to make a more accurate diagnosis.
Oral Food Challenge
For this test, your doctor will provide you
with small amounts of the foods that are suspected allergens. He or she will
steadily increase the amount of the suspected foods while monitoring your
reaction to each one.
For this task, you may be asked to wear a
mask to make your diagnosis more accurate. Some people may have a bodily
reaction simply by seeing a particular food or even thinking about it. Sometimes,
the allergist will not know (during the test) which foods he or she is giving
you as well.
This test may also be used to determine
whether an individual has a diminished response to an allergen.
of a food allergy can be difficult because several fairly common conditions can
trigger similar symptoms.
Some people lack
specific enzymes required to digest certain foods. One common food intolerance
is lactose intolerance, which can cause bloating, cramping, and other abdominal
symptoms that mimic a food allergy reaction. With this condition, dairy
products (a major source of lactose) may need to be avoided.
Toxins in foods
such as mushrooms, rhubarb, spoiled tuna, and other fish may trigger serious
reactions similar to those of a food allergy. Other causes of food-borne
illness include raw egg, undercooked meat, spoiled cheese, processed meats, and
Sulfites and other
food preservatives, monosodium glutamate (MSG), artificial sweeteners, and food-coloring
agents may spark adverse physical reactions.
Celiac disease is a
chronic digestive disorder. It is sometimes referred to as a gluten allergy,
but it is not a true allergy even though it does involve an immune system
response. This complex reaction to gluten—which is found in wheat and other
grains used primarily in baking—attacks the lining of the small intestine,
preventing the absorption of several nutrients. In its worst cases, Celiac
disease may lead to malnutrition. Milder forms of the condition result in
cramping, bloating, and abdominal pain.
Irritable Bowel Syndrome (IBS)
IBS is a digestive
disorder that can cause significant abdominal symptoms, including severe
constipation, bloating, or diarrhea. Doing your best to avoid the foods that
trigger this condition is critical to avoiding symptoms.