Allergy skin tests: Diagnosing your allergies

Pinpointing the cause of allergy signs and symptoms isn’t always easy, as there can be a number of possibilities. For instance, if you find yourself sneezing every time you stay at your parents’ house, it could be caused by the dander from their dog, a dusty guest room or maybe mold in the basement. And changes in your environment or new experiences may expose you to allergens that you didn’t even know you were sensitive to.

An allergy test given by your doctor can help you narrow down what specific substances you’re allergic to.

Allergy Relief

Some of the medications used to treat respiratory allergy symptoms include antihistamines, decongestants, nasal sprays and eyedrops.
What do medications do?
Allegra D
Allegra
Claritin-D
Flonase
Nasacort
Nasacort AQ
Nasonex
Patanol
Zyrtec

A blood test known as an in vitro allergen-specific IgE antibody test is one way to determine allergic sensitivities, but it’s not as commonly used as the allergy skin test, which is more sensitive. Using a skin test to identify the exact cause of your allergies enables your doctor to help you better control them by developing an allergy management plan that’s designed to meet your specific needs.

Purpose

Allergy testing on the skin is a simple procedure that can yield important information about your allergic sensitivities. Allergy skin tests are safe, involve little if any discomfort and can usually be done in 30 minutes or less.

The purpose of allergy skin testing is twofold:

  * To help determine whether you have an allergy

  * To identify the specific substance that’s causing your symptoms

What happens in an allergy test? It’s the same for kids and adults. Watch this video and find out. ...

A nurse usually administers the test, and a doctor who specializes in allergy problems and asthma (an allergist) typically interprets the results and determines which allergy treatment or treatments to use.

Preparation

Certain medications will interfere with an allergy skin test - primarily antihistamines. Many antidepressants, certain heartburn medications and some sleep medications also may interfere. You may need to eliminate these medications from your system before you have an allergy skin test. The amount of time it takes to rid them from your system varies. Ask your doctor about how and when to do this. Check with him or her several weeks in advance of the test and report all medications that you’re taking.

The allergy skin test procedure includes two control tests:

  * A positive control test. This test is usually histamine, which you should automatically react to. If you don’t react to the histamine, allergy skin tests may be difficult or impossible to interpret.

  * A negative control test. This test is a solution without any allergens in it, so you shouldn’t react to it. If you do, it’s probably because you have sensitive skin, and the results of the allergy skin tests will need to be interpreted with caution.

If you aren’t able to stop taking your antihistamines, your doctor may advise the in vitro allergen-specific IgE antibody test instead, because antihistamines don’t affect the results from these blood tests. Your doctor may also choose the blood test if you have a skin disorder, such as eczema (dermatitis), because testing needs to be done on clear skin.

Procedure

Before an allergy skin test, your doctor will ask you a series of questions about your symptoms and exposures. Your answers will provide clues to the cause. They may also help the doctor understand how much the symptoms interfere with your typical activities. Next, the doctor examines you. The physical exam may provide your doctor with additional clues about what’s causing your signs and symptoms.

After interpreting the information gathered from your allergy history and physical exam, your doctor may recommend an allergy skin test. There are numerous allergens for which you can be tested. But your doctor will order testing only for those allergens considered likely causes of your allergies.

For instance, if you came to the doctor because you sneezed repeatedly after playing with your neighbor’s cat, testing for sensitivity to insect bites may be unnecessary. But because pet dander is a common cause of hay fever (allergic rhinitis) and asthma, your doctor will likely include it among the allergens he or she tests for.

The test may be performed on your forearm or back using a common procedure called the prick technique.

During the test, you can expect:

  1. The test area is cleaned with alcohol.
  2. A pen is used to label the test area with small marks that indicate where each allergen will be applied.
  3. Extracts of allergens are applied in tiny drops next to each mark.
  4. After all of the drops are placed, a small instrument called a lancet is used to prick the skin through each drop. A new lancet is used for each scratch. The surface of your skin is penetrated just enough so that the extract can enter and interact with the skin.
  5. Droplets are left on the skin for about 20 minutes.

After the test

If an allergen provokes an allergic reaction, you’ll develop a raised, red, itchy bump (wheal) that may look like a mosquito bite. Your doctor will then physically measure the reaction.

After the test results are recorded, the skin in the test area is cleaned with alcohol to remove all of the ink and the allergen droplets. You may experience some itching at the sites of the skin pricks. A mild cortisone cream may help relieve the itching.

The length of time the itching persists varies, depending on the extent of the reaction. If you have several reaction sites, the redness may continue until the next day. Generally, the itching is worst during the 20-minute waiting period and then fades fairly quickly.

Results

A positive skin test means that you may be allergic to a particular substance. In general, the bigger the reaction, the more sensitive you are. A negative skin test means that you probably aren’t allergic to that particular allergen.

To pinpoint the cause of your signs and symptoms, your doctor will consider the results of your skin test, your allergy history and the results of your physical exam. Your doctor will review and interpret the results and suggest the best way to manage your allergies. Treatment may include medications and allergy shots (immunotherapy) or steps to avoid allergens.

Who should have one?

Allergy skins tests can be helpful for both children and adults if allergy is suspected as a possible cause of a medical problem. If your doctor suspects you have hay fever, asthma, a penicillin allergy or a stinging insect allergy, consider allergy testing.

Pros and cons

The advantage of allergy skin testing is that it not only can confirm an initial diagnosis of allergies, but it may pinpoint the exact cause. Based on the results of the test, your doctor can suggest the most effective methods for controlling your symptoms. For example, if you’re allergic to pollen, your doctor may suggest that you run an air conditioner at home as much as possible during pollen season. In other cases, allergy tests can provide reassurance that you aren’t allergic to something you might have suspected.

The disadvantage of allergy skin testing is that it can’t be done for every possible allergen, so some allergies may not be identified. Your doctor may suggest that you skip the allergy tests and go directly to allergy medications. If allergy medications work and don’t cause side effects, then allergy testing may not be necessary. If allergy medications don’t work or they cause side effects, then you may want to consult with an allergist and proceed with testing.

Provided by ArmMed Media
Revision date: July 9, 2011
Last revised: by Sebastian Scheller, MD, ScD