Allergy Testing

More than 50 million people in the United States have allergies. Finding out what you are allergic to is an important first step to effective allergy treatment. Today allergy tests are more convenient and accurate than ever before. When combined with a detailed medical history, allergy testing can identify the specific things that trigger your allergic reactions.

Are there any allergy testing side effects?

Any medical test involves some risk. The risk with allergy skin tests is that allergy symptoms might occur during the test. The most common symptoms are itching and swelling of the skin where the tests are. In rare cases, a more serious reaction can occur. That is why skin tests should be done by a specialist. The risk with allergy blood tests is pain or bleeding at the needle mark. Also, a few people may faint during blood testing.

What about allergy testing in children? Who can be tested for allergies?

Adults and children of any age can be tested for allergies.

How do allergy skin tests work?

There are two types of skin tests. During the first type of skin test, a drop of a suspected allergen is pricked or scratched on the surface of the skin. The test is performed on the back or forearm. Many suspected allergens are tested at the same time. If you are allergic to one of the tests, you will have redness and swelling at the test spot. Sometimes the doctor will recommend a second type of test. In this type, a small amount of the suspected allergen is injected into the skin of the arm or forearm. Several suspected allergens are tested at the same time.

How long does it take to get skin test results?

Skin testing is fast. For both types of skin tests, positive reactions usually appear within 20 minutes. Sometimes redness and swelling can occur several hours after skin testing. The delayed reaction usually disappears in 24 to 48 hours, but should be reported to the doctor or nurse.

Is skin testing painful?

Both types of skin tests have little or no pain. However, positive reactions cause annoying itching red bumps which look and feel like mosquito bites. The itching and bumps are gone usually in just a few short minutes or hours.

Does medicine interfere with allergy skin tests?

Some medicines do interfere with allergy skin tests. The doctor of nurse will tell you if you need to change your medicine before allergy skin testing.

When are allergy blood tests used?

An allergy blood test is often used because:

• The patient is taking a medicine that can interfere with skin testing, but cannot be stopped for a few days
• The patient suffers from a severe skin condition such as eczema or psoriasis
• Testing with a strong allergen might cause an extra large positive reaction
• For babies and very young children, a single needle stick for allergy blood testing may be better than several skin tests.

How long does it take to get blood test results?

Because the blood sample must be sent to a lab for testing, it takes many days to get the results.

Which test method is best?

Skin tests give fast results. They usually cost less than allergy blood tests. What are the negatives? Young children do not like this type of test. Some medicines can interfere with the tests. In addition, in some people with dark skin it may be hard to read the tests. Also, the skill of the tester may affect the results. The test should be done by a person with training.

Blood tests are helpful because they involve a single needle prick. Medicine does not interfere with the results. However, it takes a long time to get the results. Blood tests cost more than skin tests. There are many of types of allergy blood tests. Some types are more helpful than others.

Each test method has pluses and minuses. The test results alone do not diagnose allergies. All test results, from either type of test, must be interpreted together with the medical history.

What allergies can allergy testing find?

A blood test for allergies can help find allergies to pollen, molds, dust mites, animal dander, insect stings, foods and some medicines.

Food Allergy Testing

In a food allergy skin test, a very small drop of a liquid food extract, one for each food, is placed on the skin. The skin is then lightly pricked. This is safe and generally not painful. Within 15 to 20 minutes, a raised bump with redness around it, similar to a mosquito bite, may appear. It shows that you are probably allergic to that food and you probably need food allergy treatment.

Sometimes, an allergy blood test may be used. The blood test generally costs more than skin testing. The results are usually not ready for one to two weeks.

If done right, skin tests or blood tests are reliable and can rule in or out food allergy. Some people do test "allergic" to a food (by skin or blood testing) and yet have no symptoms when they eat that food. To confirm test results, your allergist may ask you to do a challenge test. This means that you have to eat or drink small portions of a food in increasing amounts over a period of time to see if an allergic reaction occurs. This is usually done under a physician’s supervision.

How do allergists tell which foods make me sick?

Some people know exactly what food causes their allergy. They eat peanuts or a product with peanut in it and immediately break out in a rash. Others need a doctor’s help in finding the cause. Sometimes, the symptoms show up many hours after they have eaten the food.

Your allergy treatment will typically begin with a complete medical history. Your allergist will ask you about:

• The symptoms you have after eating the food
• How long after eating the food these symptoms occur
• How much of the food you had
• How often has the reaction occurred
• What type of medical treatment, if any, you have had
• The medical history will also include questions about your diet, your family's medical history, and your home and living area.

Your allergist asks these questions to find out what is causing your allergy or making your symptoms worse. Allergy to pollen in the air, such as ragweed pollen, can be the cause of the swelling or itching in your mouth and throat if you eat certain foods like melons. There is no food allergy cure.

Can special diets help pinpoint the problem?

Your allergist may narrow the search for foods causing allergies by placing you on a special diet. You may be asked to keep a daily food diary. It lists all food you eat and medication you take, along with your symptoms for the day. If only one or two foods seem to cause allergies, you may try avoiding them. In this diet, you do not eat the suspect food at all for one to two weeks. If the allergic symptoms decrease during that period and flare up when you eat the food again, it is very likely the food causing your allergy. However, which food you should avoid (and for how long) and when you should eat the food again (if ever) should be decided together with your allergist. You should never try to eat even a small quantity of any food you and your allergist have decided against. Your allergist may want to confirm these diet tests with a challenge test. Food allergy testing is a very important step.