Allergy Tests

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Allergy Testing Identifies Triggers

There are several tests available to doctors who want to determine the underlying cause of a patient's nasal allergy symptoms in order to formulate an appropriate treatment program. These tests help isolate the specific trigger or triggers that cause the immune system to overreact. The most common types are skin tests or blood tests. Ask your doctor or allergist if one of these tests might help.

Allergy Skin Tests

The most common allergy skin test is a "skin prick test," in which drops of purified allergen extracts are pricked, punctured, or scratched into your skin to see what specific allergen is causing a reaction.

Skin prick tests are usually done with a needle on the arm or back. If you are allergic to one of the substances being tested, a hive-like red, itchy bump, or "wheal" will appear, usually within about 15 minutes. The more pronounced the reaction, the more severe your allergy to that substance.

In another type of skin test, called an intradermal, or injection test, a small amount of an allergen is injected under the skin. This is a more sensitive test than a skin prick test, and may be done if prick test results are negative.

Allergy Blood Tests

A blood test, or RAST (radioallergosorbent) test may be performed if a skin test cannot be done for some reason, like if you are taking certain medications, have a fear of needles, or if you have severe hypersensitivity to a particular allergen. This type of blood test uses radioactive or enzyme markers to detect levels of antibodies reacting to allergens. Since blood tests require lab analysis, results are not available as immediately as they are with skin tests.

Other acceptable but less common allergy test methods include the "scratch test" and the "challenge test." In a scratch test, the skin is scratched, and then the allergen is dropped onto the site of the scratch. This test is not in common use.

In a challenge test, small amounts of an allergen are introduced to the mouth, or by inhalation, or other approaches. These tests are more commonly done for food or medication allergies than for nasal allergies, and they must be closely supervised by a doctor.

Test Accuracy

Skin tests and blood tests are both very reliable and accurate in determining a person's particular allergies. Each test is estimated to be approximately 90 percent accurate. Ask your doctor or allergist if one of these tests might help to confirm the diagnosis and to determine the exact cause of your or your child's nasal allergies.