Allergy Tests

About 1 in 5 people have allergies to things they breathe in, eat, or touch. That works out to about 50 million people with allergies in the United States.

Some different substances can cause an allergic reaction, including peanuts and shellfish, insect stings, pollen, dust, and pet dander.

When individuals with allergies are exposed to these substances, their immune system mistakenly reacts as if the allergen were a dangerous foreign invader.

It creates a type of antibody called immunoglobulin E (IgE), which triggers symptoms like these:

• wheezing
• coughing
• runny or stuffed nose
• itchy skin or rash
• nausea and vomiting
• diarrhea

Treatments are available to relieve allergy symptoms. But first, your doctor needs to determine what is causing them.

Allergy tests expose you to small amounts of different substances that trigger allergies, called allergens.

How you respond to these tests can determine whether you have an allergy and what you are allergic to receive the right treatment.

WHO NEEDS ALLERGY TESTS?

Doctors perform allergy tests on people who have reacted substances such as:

• pollen or grass (called allergic rhinitis)
• foods such as nuts, fish, milk, eggs, wheat, or soy
• dust
• mold
• insect stings
• pets
• medicines
• household chemicals, such as those found in various cleaners, dyes, and perfumes
• latex

TYPES OF ALLERGY TESTS

Allergy tests can be performed in one of two ways: with a skin test or blood test.

Skin tests are most common, and they are most accurate at diagnosing allergies to substances like pollen, pet dander, dust, and food.

Blood tests are another option. This type of test is not used as often as the skin test because it isn’t as effective at picking up allergies, and it is more expensive.

However, it may be an option if you have severe allergies or take a medication that could interfere with the skin test result.

WHAT TO EXPECT

Allergy tests are performed at a doctor’s office. Some tests can detect an allergic reaction within just a few minutes after you’re exposed to the offending substance.

Before you get tested, the doctor will ask questions about your symptoms, including how long you have had them and what seems to trigger them.

A skin prick test places a small amount of the substance under the skin of your forearm. First, the health care provider cleans your skin with alcohol.

Then, a pen marks each place on your skin where allergens will be tested. A small amount of a substance like pollen, animal dander, or mold is placed just under your skin’s surface with a small needle.

A couple of substances can be tested at one time. A control test is also done on your skin using histamine.

This is the same substance your immune cells release during an allergic reaction. Your doctor will use histamine control as a comparison to gauge your reaction to the allergens.

After about 20 minutes, the health care provider will check your skin for signs of red, itchy bumps called wheals.

A wheal looks like a mosquito bite. It is a sign of an allergic reaction. The larger the wheal, the more allergic you are to the substance.

A skin injection or intradermal test injects a small amount of the allergen into the skin of your arm using a needle.

After a few minutes, your arm is checked for signs of an allergic reaction. This test is more sensitive than the skin prick test.

Your doctor can use it if the skin prick test result was negative or diagnose an allergy to insect stings or medication.

A patch test places a small sample of the allergen on your skin with a sticky patch. This type of test is used to diagnose the cause of skin rashes called contact dermatitis.

It can test for reactions to substances like latex, medications, and scents. You will wear the patches on your upper arm or back for two days, then return to your doctor’s office to see if they have caused a reaction.

A challenge test gives you a small amount of the substance to breathe in or eat. This type of test is used for food or medication allergies.

A blood test takes a small sample of your blood through a needle placed in a vein. The blood is evaluated for the presence of IgE, an antibody your body produces during an allergic reaction.

Doctors use this test if a skin prick test would not be safe because of a severe allergy or taking medications that might affect your test results.

RISKS OF ALLERGY TESTS

It is common to have swollen; itchy red bumps appear on your skin if you are sensitive to the substance used in the test.

These bumps should subside after an hour or so, but they can last for a few days in some cases.

If you are severely allergic to the substance used in the test, there is a small chance that you can have a severe and possibly life-threatening reaction.

The staff at your doctor’s office have treatments to stop this kind of reaction.

Allergy tests can sometimes cause false-positive or false-negative results. This means the test finds an allergy when none exists, or it doesn’t find an allergy that does exist.

You may need to do the test 2 times to confirm the valid results.

Some medicines can affect the results of allergy tests.

Before the test, tell your doctor about every drug you take, even if you buy it over the counter. You may need to quit using these medicines a week or more before the test:

• prescription and over-the-counter antihistamines such as levocetirizine (Xyzal), loratadine (Alavert, Claritin), and diphenhydramine (Benadryl)
• tricyclic antidepressants, as desipramine (Norpramin) and nortriptyline (Pamelor)
• heartburn medications such as cimetidine (Tagamet) and ranitidine (Zantac)
• asthma drugs such as omalizumab (Xolair)

WHO SHOULDN’T BE TESTED?

You may not be allowed to get tested if you’ve had a severe reaction to a substance called anaphylaxis.

This reaction causes symptoms like trouble breathing, tightness of the throat, dizziness, fainting, and a rapid heartbeat.

In some people, exposure to even a tiny amount of the substance can be life-threatening.

WHAT HAPPENS AFTER THE TEST?

An allergy test will help determine what substances cause you to react. Once you know, you can avoid those substances.

Your doctor can also place you on a treatment plan to relieve symptoms if exposed to your allergen(s).

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