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Testing for Allergies
By Dr. Keith Applegate
Asthma
and allergies
affect more
than 60 million
Americans, but
these conditions are often overlooked. Testing for allergies can
help you discover what you might
be allergic to and enable your physician to prescribe treatment.
Allergy tests are usually combined with a physical examination
and medical history. Testing done
by an allergist or family practice
physician is generally safe and effective for adults and children of all
ages.
There are two main types of
allergy testing: skin or scratch testing and in vitro or blood testing.
Skin or scratch testing is also
known as a puncture or prick test.
Scratch testing involves placing a
very small amount of an extract
containing possible allergens such
as pollen, mold, dust mites and animal dander in a small indentation
or prick on the surface of the skin.
The skin is scratched with a needle
at the extract site, and the areas are
inspected after several minutes for
signs of redness and/or swelling.
A number of variables influence
reactivity, including the patient’s
age and the color of his or her skin.
The drawbacks for this type of testing include the need for multiple
intradermal injections. It is also
more painful and takes up to 20
minutes to perform. The strength
or quality of the extract used in the
test may vary, and some medications such as antihistamines, beta
blockers and sleep aids interfere
with results. You must stop taking
these medications prior to undergoing testing. It is also difficult to
reproduce the results. There may be
a risk of anaphylactic shock if your
body reacts unexpectedly to one of
the allergens.
Allergy blood testing detects and
measures the amount of allergenspecific antibodies in your blood.
This type of test can be used when
skin tests might be unsafe or if the
patient prefers a blood draw. A lab
will test the blood sample to measure the level of a type of antibody
called immunoglobulin E or IgE.
The body makes IgE in response
to certain allergens. IgE levels are
usually higher in patients with allergies or asthma. Allergy blood tests
usually screen for at least 10 of
the most common allergy triggers,
including dust, pet dander, trees,
grasses, weeds and molds that grow
where you live. The tests are also
particularly helpful for diagnosing
food allergies.
In vitro tests are more specific
than scratch testing. They offer a
shorter testing time, and patients
don’t have to stop taking their
medications. In vitro tests work
better for patients with skin problems, those who cannot tolerate the
many needle scratches required for
skin testing and those who have an
unstable heart condition or poorly
controlled asthma. The results indicate the degree of patient sensitivity
to particular allergens, which helps
predict initial doses for immunotherapy. With in vitro (blood) tests,
there is no risk of anaphylactic
shock, and the patient’s age or skin
color does not affect reactivity. The
test can be customized, and a serum
sample may be stored for later
testing of additional allergens. Be
sure to discuss your allergy-testing
options thoroughly with your physician.
About the Author
A Louisville native, Dr. Keith Applegate
joined Family Practice Associates of
Lexington in 1987. Dr. Applegate’s
objective is “to have a helpful and
rewarding doctor-patie