Allergy Testing

What Happens During an Allergy Test?

If your family doctor thinks you might have an allergy, he or she will probably refer you to an allergist (a doctor who specializes in diagnosing and treating allergies) for further testing.

Here's what to expect.

An allergist will ask questions, such as:

• What symptoms do you notice when you have a reaction? (e.g., hives or a scratchy throat)
• How often does the reaction happen?
• How long does it take between eating a particular food and the start of the symptoms?
• Do any family members have allergies or conditions like eczema and asthma?

The allergist will probably also do tests. Skin tests are the most common type of testing used to diagnose allergies.

Skin Tests

In a typical skin test, a doctor or nurse will place a tiny bit of an allergen (such as pollen or food) on the skin, then make a small scratch or prick on the skin. Allergists usually do skin tests on a person's forearm or back. The allergist then waits 15 minutes or so to see if reddish, raised spots (called wheals) form, possibly indicating an allergy.

Sometimes, doctors may do a similar test, called an intradermal test, under the surface of the skin. This type of test is usually done to look for environmental allergies.

If the doctor thinks a person might be allergic to more than one thing — or if it's not clear what's triggering a person's allergy — the allergist will probably skin test for several different allergens at the same time.

Skin tests may itch for a while. The allergist might give you antihistamine or steroid cream after the test to lessen the itching.

Testing for Food Allergies

Doctors can also use skin tests to diagnose food allergies. But it's different with food allergies. When a skin test shows up as positive for a certain food, that only means a person might be allergic to that food. In these cases, doctors may want to do additional testing.

To diagnose a food allergy for certain, an allergist may do a blood test in addition to skin testing. This involves taking a small sample of a person's blood and sending it to a laboratory for analysis. The lab checks the blood for IgE antibodies to specific foods. If there are enough IgE antibodies to a particular food in the blood, it means it's very likely that person has an allergy.

Doctors often use a combination of skin testing and blood testing to diagnose a food allergy. If both come up positive, there's no need for further testing.

If the results of the skin and blood tests are still unclear, though, an allergist might do something called a food challenge. During this test, the person is given gradually increasing amounts of the potential food allergen to eat while the doctor watches for symptoms.

Because food allergies can trigger serious reactions in people, this test can be risky. So it needs to be done in an allergist's office or hospital that has access to medications and specialists to control reactions like anaphylaxis. Doctors only occasionally use the food challenge to diagnose a person with a food allergy. Most of the time, this type of test is done to find out if someone has outgrown a known allergy.

Test Results and Treatment

If an allergist decides that a person has an allergy, he or she will recommend a course of action. Treatment depends on the allergy — for people with environmental allergies, this might mean the allergist prescribes medication or allergy shots. For a food or other allergy, the allergist will advise the patient on ways to avoid the allergen.