What Happens During an Allergy Test?
If your family doctor thinks you might have an allergy, he or
she will probably refer you to an allergist (a doctor who
specializes in diagnosing and treating allergies) for further
testing. Here's what to expect.
An allergist will ask questions, such as:
- What symptoms do you notice when you have a reaction? (e.g.,
hives or a scratchy throat)
- How often does the reaction happen?
- How long does it take between eating a particular food and
the start of the symptoms?
- Do any family members have allergies or conditions like
eczema and asthma?
The allergist will probably also do tests. Skin tests are the
most common type of testing used to diagnose allergies.
Skin Tests
A skin prick or scratch test involves placing liquid extracts of
allergens (such as pollen or food) on a person's forearm or
back, then pricking the skin a tiny bit. The allergist then waits
15 minutes or so to see if reddish, raised spots (called wheals)
form, indicating an allergy.
A few doctors may do a similar test, called an intradermal test,
under the surface of the skin. This type of test is usually done to
look for environmental allergies.
If the doctor thinks a person might be allergic to more than one
thing - or if it's not clear what's triggering a
person's allergy - the allergist will probably skin test for
several different allergens at the same time.
Skin tests may itch for a while. The allergist might give
you antihistamine or steroid cream after the test to lessen the
itching.
Testing for Food Allergies
Doctors use skin tests to diagnose environmental allergies. But
it's different with food allergies. When a skin test shows up
as positive with a certain food, that only means a person
might
be allergic to that food. In these cases, doctors may want to do
additional testing.
To diagnose a food allergy for certain, an allergist may do a
blood test in addition to skin testing. This involves taking a
small sample of a person's blood and sending it to a laboratory
for analysis. The lab checks the blood for IgE antibodies to
specific foods. If there are enough IgE antibodies to a particular
food in the blood, it means it's very likely that person has an
allergy.
Doctors often use a combination of skin testing and blood
testing to diagnose a food allergy. If both come up positive,
there's no need for further testing.
If the results of the skin and blood tests are still unclear,
though, an allergist might do something called a food challenge.
During this test, the person is given gradually increasing amounts
of the potential food allergen to eat while the doctor watches for
symptoms.
Because food allergies can trigger serious reactions in people,
this test can be risky. So it needs to be done in an
allergist's office or hospital that has access to medications
and specialists to control reactions like anaphylaxis. Doctors only
occasionally use the food challenge to diagnose a person with a
food allergy. Most of the time, this type of test is done to
find out if someone has outgrown a known allergy.
Test Results and Treatment
If an allergist decides that a person has an allergy, he or she
will recommend a course of action. Treatment depends on the allergy
- for people with environmental allergies, this might mean the
allergist prescribes medication or allergy shots. For a food or
other allergy, the allergist will advise the patient on ways to
avoid the allergen.
Reviewed by:
Hemant P. Sharma, MD
Date reviewed: January 2008
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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