Why It Is Done
Allergy testing is done to find out what
substances (allergens) may cause an allergic reaction.
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).
- Find out whether
a person may have a drug allergy or be allergic to 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 likely 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 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.
- Check the skin after 12 to 15 minutes for red,
raised itchy areas called wheals. If a wheal forms, it means you are possibly allergic
to that allergen (this is called a positive reaction).