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Allergy Tests

(continued)

Risks

Skin tests

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.

Blood test

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 You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.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.

Results

A skin or blood test can tell you what substance, or allergen, may trigger an allergic response.

Skin tests

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**
Normal (negative):	No raised red areas (called wheals) are created by the allergen.
Abnormal (positive):	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.

Blood tests

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**
Normal (negative):	The levels of immunoglobulin E (IgE), a type of antibody, are the same as in a person who does not have allergies.
Abnormal (positive):	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 sweating.
Getting a skin patch wet.
Taking medicines such as antihistamines or tricyclic antidepressants.

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WebMD Medical Reference from Healthwise

Last Updated: June 30, 2011

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.