The major risk with the skin prick test
or the intradermal skin test is a severe allergic reaction called
anaphylaxis. Symptoms of a severe allergic reaction
include itching, wheezing, swelling of the face or entire body, trouble
breathing, and low blood pressure that can lead to
shock. An anaphylactic reaction can be
life-threatening and is a medical emergency. Emergency care is always needed
for an anaphylactic reaction. But severe allergic reaction is rare, especially
with the skin prick test.
If you are having a skin patch test and
you have severe itching or pain under any of the patches, remove the patches
and call your doctor.
There is very little risk of a problem
from having blood drawn from a vein.
- You may develop a small bruise at the
puncture site. You can reduce the risk of bruising by keeping pressure on the
site for several minutes after the needle is withdrawn.
- In rare
cases, the vein may become inflamed after the blood sample is taken. This
condition is called phlebitis and is usually treated with a warm compress
applied several times daily.
- Continued bleeding can be a problem
for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other
blood-thinning medicines can also make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood is drawn.
A skin or blood test can tell you what
allergen, may trigger an
Skin tests work by exposing a person
to suspected allergens and seeing if a reaction occurs. The results of the skin
tests will be available immediately after testing is done.
Allergy skin tests
No raised red areas (called wheals) are created by the
A wheal created by the allergen is at least 1/8 inch
(3 mm) larger than the reaction to the negative control. The larger the wheal,
the more certain it is that the person is allergic to that specific allergen.
Allergy blood tests look for
substances in the blood called antibodies. Results of allergy blood tests are
usually available in about 7 days.
Allergy blood tests
The levels of immunoglobulin E (IgE), a type of
antibody, are the same as in a person who does not
The levels of immunoglobulin E (IgE) antibodies for a
particular allergen or group of allergens are 4 times the normal level.
What Affects the Test
Reasons you may not be able to
have a skin test or why the results may not be helpful include:
- Exercise that causes excessive
- Getting a skin patch wet.
- Taking medicines
antihistamines or tricyclic antidepressants.