Allergy Testing Supports Targeted Treatment

From pollens to peanuts, the variety of substances that can cause allergies is vast. Dust, mites, molds, plants and favorite pets are among the many things containing particular proteins that don't bother most people but provoke significant immune responses in others. Any substance that causes an allergic reaction is called an allergen.

Accurate identification of the exact cause of an allergic reaction is an essential tool in diagnosis and treatment. Allergy testing helps determine if medication is appropriate, for example, or whether lifestyle changes are in order to distance the patient from the allergen or the allergen from the patient.

Allergies are the sixth-leading cause of chronic disease in the US, according to the National Institute of Allergy and Infectious Diseases, affecting to some degree as many as 50 million people. Allergy and asthma incidence is rising, so testing has taken a more universal role in health care.

"Testing is necessary for anyone who needs identification of specific allergens," said Asriani M. Chiu, MD, Medical College of Wisconsin Assistant Professor of Pediatrics and Medicine (Allergy).

"If you have somebody who only has 'hay fever' symptoms, such as runny nose, itchy nose and sneezing, and itchy watery eyes, and they only experience symptoms in the fall - symptoms that go away by the end of the first frost - you really don't need an allergist to tell you it's ragweed.

"On the other hand, for somebody who has year-round allergy symptoms, even if certain seasons worsen it, what you're trying to distinguish is whether it is caused by something that's only present inside the home year-round, or could they have multiple seasonal allergies? The allergy testing is going to help identify the problem. Testing is also appropriate for skin rashes if it's not clear if the rash is related to an allergy."

Determining When to Test
There's no cut-and-dried "formula" to discover who needs allergy testing and when they need it. If cold-like symptoms persist for a long time, recur the same time of year, include a lot of itching, and an over-the-counter hay fever remedy doesn't provide relief, testing might be in order to identify possible allergens.

Asthma-type symptoms such as chest tightness, difficulty breathing, coughing, and wheezing can be serious and dangerous and even, in severe cases, life-threatening. Finding the cause can help improve quality of life when treatment is tailored as much as possible to specific allergens.

"Let's say, for example, that medications aren't working well," said Dr. Chiu, "or there may be some side effects to the medication, or the person is very wisely saying 'I don't want to just use the medicines, I want to know what I am allergic to.' Those would be very reasonable issues indicating that it's time to get the testing done."

Dr. Chiu practices at the Children's Hospital of Wisconsin Asthma/Allergy Center and at the Zablocki VA Medical Center. She noted that allergy tests are performed similarly for both children and adults, and the Asthma/Allergy Center treats all ages.

Skin Tests and Blood Tests
"There are two forms of allergy testing in general," said Dr. Chiu. "Skin tests are done in an allergy doctor's office - that's what most people tend to expect when they talk about allergy testing. Skin testing is looking for reaction to a specific allergy antibody called IgE because the IgE is what causes the immediate allergic reaction and the resulting symptoms.

"When you get skin testing done, whether it's for environmental allergens like ragweed, grass, or mold, or for foods, you're getting little 'prickle' tests on your back or on your arms. Some people might feel that it's a little bit uncomfortable, but in general it's very well tolerated, even in young children. What we're trying to do is see if you get what we call a 'wheal and flare' reaction on the skin site (a red itchy bump).

"The second type of allergy testing is blood testing. We use that if you have a rash that's so prominent you can't get the skin testing done. Or you may be on a medication that interferes with the correct interpretation of skin testing; these include antihistamines and some of the older antidepressants."

Patients on beta blocker medications are also candidates for blood testing instead of skin testing. "That's very important," said Dr. Chiu. "If you're on a beta blocker to treat high blood pressure or after a heart attack, or even some eye drops used to treat glaucoma, that medication can make it harder to treat people who do have a severe reaction to the test. So whenever we see someone on a beta blocker, we don't do allergy skin testing, we do the blood test instead."

Advantages and Disadvantages
During skin tests small amounts of actual allergens are "injected" just under the skin to see if the person is reactive to the allergens, while blood tests look for the unique antibodies that do the reacting. In general terms, Dr. Chiu said, the tests are about the same in overall accuracy. However, she added, in certain cases there seems to be an indication that there may be more sensitivity in the skin testing.

As a result, "if we can do the skin testing we prefer to do the skin testing. The advantage of skin testing is that it is going to be more immediate. You can get the answers within twenty minutes, so during that visit you're going to be able to identify what you are allergic to.

"The blood test, because it's a lab test, can take up to a week or ten days depending on where the analysis is done, so you don't get the answers as immediately. And then of course it's a blood draw, and some people have issues with blood draws.

"Obviously, if you're doing skin testing, you're taking something that's potentially allergenic, like ragweed or cat dander or whatever, so a potential disadvantage is that if you are a highly allergic individual and if for example your asthma is not very well controlled, the allergy testing itself can cause an allergic reaction. That's why in a doctor's or allergist's office you want first of all to make sure that your asthma symptoms are controlled and that you are still on your asthma medication. There are risks, but they are very minimal compared to the amount of allergy testing that goes on, and considering the important information you can get from the results."

Dan Ullrich
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.