Why It Is Done continued...
The skin prick test can also be done
- Identify inhaled (airborne) allergens, such
as tree, shrub, and weed pollens, molds, dust, feathers, and pet
- Identify likely food allergens (such as eggs, milk,
peanuts, nuts, fish, soy, wheat, or shellfish).
- Determine whether
a person may be allergic to a
medicine or insect venom.
A blood test on a blood sample may be
done instead of a skin prick test if a person:
hives or another skin condition, such as
eczema, that makes it hard to see the results of skin
- Cannot stop taking a medicine, such as an
antihistamine or tricyclic antidepressant, that may
prevent or reduce a reaction to a substance even when a person is allergic to
- Has had a severe allergic reaction (anaphylaxis).
- Has had positive skin tests
to many foods. Enzyme-linked immunosorbent assay (ELISA) can find out the foods
that a person is most allergic to.
How To Prepare
Many medicines can affect the results of
a skin test. Be sure to tell your doctor about all the
nonprescription and prescription medicines you take.
You may need to stop taking some medicines, such as some tricyclic
antihistamines such as cetirizine (Zyrtec),
fexofenadine (Allegra), and loratadine (Claritin), before you have an allergy
Talk to your doctor about any concerns
you have regarding the need for the test, its risks, how it will be done, or
what the results will show. To help you understand the importance of this test,
fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional doing the
skin prick or intradermal test will:
- Clean the test site (usually on your back or
arm) with alcohol.
- Place drops of the possible allergens on your
skin about 1 in. (2.5 cm) to
2 in. (5 cm) apart. This allows
many substances to be tested at the same time.
- Prick the skin under
each drop with a needle. The needle passes through the drop and allows some of
the allergen to penetrate your skin. For the intradermal test, a needle is used
to inject the allergen solution deeper into the skin. See a picture of a
skin prick allergy test .
- Check the skin after 12 to 15 minutes for red,
raised itchy areas called wheals. If a wheal forms, it means you are allergic
to that allergen (this is called a positive reaction).
An alternative skin prick method uses a device with 5 to
10 points (heads), which are dipped into bottles that contain the allergen
extract. This device is pressed against the skin of the forearm or back so that
all heads are pressed into the skin at the same time.