Allergy Tests

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 3 mm (1/8 inch) 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. See a picture of a positive patch test reaction.

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.

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Author:	Debby Golonka, MPH Ralph Poore	Last Updated: September 27, 2007
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Harold S. Nelson, MD - Allergy and Immunology Donald Sproule, MD, CM, CCFP, FCFP - Family Medicine
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