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What is an allergy skin test?
An
allergy skin test, also called a scratch test, is used to identify the
substances that are causing your allergy symptoms. It is performed by applying
an extract of an allergen to your skin, scratching or pricking the skin to allow
exposure, and then evaluating the skin’s reaction.
How is an allergy skin test performed?
First, a doctor
or nurse will examine the skin on your forearm and clean it with alcohol.
(Sometimes, this test is performed on an area of the back). Areas on your skin
are then marked with a pen to identify each allergen that will be tested. A drop
of each potential allergen extract – such as pollen, animal dander, or insect
venom – is placed on the corresponding mark on your skin. A small disposable
pricking device is then used so that the extract can enter into the outer layer of
the skin (the epidermis). The skin prick is not a shot and doesn’t cause
bleeding.
Sometimes, instead of the skin pricking method, a small amount of the
allergen is injected just under the skin. If there are allergic antibodies in
the skin, your skin will become irritated and may itch, much like a mosquito
bite. This reaction means you are allergic to that substance.
How long does the test last?
Plan to
spend about an hour for the entire appointment. The allergen placement part of
the test takes about 5 to 10 minutes. Then you will have to wait about 15
minutes to see how your skin reacts.
How can I prepare for the test?
Inform
the health care provider who is going to perform the skin test about all
medications you are taking, including over-the-counter medications.
Over-the-counter antihistamines stop allergic reactions and should not be
taken for at least 48 hours before the test. Prescription antihistamines should
be discontinued 5-7 days before the test. Talk to your doctor about
discontinuing your prescription medications before the test.
Your doctor will give you a list of medications to avoid before the test,
since there are other medications that will interfere with the results. Since you
may not be able to discontinue certain medications before the test, the doctor
or nurse may perform a separate "control" test to determine if that
particular drug will interfere with the skin test.
Will the skin test hurt?
The test may be mildly
irritating, but most people say it doesn’t hurt too much.
Is the test safe?
Although small
amounts of allergens are introduced into your system, a skin test is completely
safe when performed properly.
What happens after the test?
The
extracts and ink marks will be cleaned off your skin with alcohol. A mild
cortisone cream will be applied to your arm to relieve any itching that may
occur at the sites of the skin pricks. Keep the tested area on your arm
uncovered when you go home. Your doctor or allergist will use the results of the
test to help develop a management plan for you.
When should I call my doctor?
Call
your doctor if you experience any of the following symptoms:
- Fever
- Lightheadedness
- Wheezing
- Shortness of breath
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