Allergies

Allergy testing involves having a skin or blood test to find out what substance, or allergen, may trigger an allergic response in a person. Skin tests are usually done because they are rapid, reliable, and generally less expensive than blood tests, but either type of test may be used.

Skin tests

A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops. There are three types of skin tests:

• Skin prick test. This test is done by placing a drop of a solution containing a possible allergen on the skin, and a series of scratches or needle pricks allows the solution to enter the skin. If the skin develops a red, raised itchy area (called a wheal), it usually means that the person is allergic to that allergen. This is called a positive reaction.
• Intradermal test. During this test, a small amount of the allergen solution is injected into the skin. An intradermal allergy test may be done when a substance does not cause a reaction in the skin prick test but is still suspected as an allergen for that person. The intradermal test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen (false-positive test results).
• Skin patch test. For a skin patch test, the allergen solution is placed on a pad that is taped to the skin for 24 to 72 hours. This test is used to detect a skin allergy called contact dermatitis.

Blood tests

Allergy blood tests look for substances in the blood called antibodies. Blood tests are not as sensitive as skin tests but are often used for people who are not able to have skin tests.

The most common type of blood test used is the enzyme-linked immunosorbent assay (ELISA, EIA). It measures the blood level of a type of antibody (called immunoglobulin E, or IgE) that the body may make in response to certain allergens. IgE levels are often higher in people who have allergies or asthma.

Other lab testing methods, such as radioallergosorbent testing (RAST) or an immunoassay capture test (ImmunoCAP, UniCAP, or Pharmacia CAP), may be used to provide more information.

Your allergy test results may show that allergy treatment is a choice for you.

Allergy shots are a type of immunotherapy to help treat allergic rhinitis and allergic asthma. Small doses of substances (allergens) are injected under the skin. This may help your immune system reduce or eliminate sensitivity to the allergen that causes an allergic reaction.

A doctor will do skin or blood tests to find out what the person is allergic to. Allergy shots are available for some allergies to:

• Pollen (ragweed, grasses, trees).
• House dust mites and cockroaches.
• Animal dander (dogs and cats).
• Mold (fungus).
• Insect venom (wasps, bees, yellow jackets, hornets, fire ants).

How well do allergy shots for allergic rhinitis work?

Allergy shots are effective in treating allergic rhinitis and allergic asthma. The shots reduce symptoms in those allergic to pollens, animal dander, dust mites, mold, and cockroaches. Experts do not know how long allergy shots work after you stop getting the shots. Some people may not have their allergies return. Others may have allergies return within a few years.

Although you still need to avoid allergens, you may be able to use less medicine or stop using medicines.