Skin Test for Allergy

1 What is a Skin Test for Allergy?

During allergy skin test, your skin is exposed to supected allergens (allergy causing agents) and is then observed for signs of an allergic reaction.

Together with you medical history, allergy test may be able to determine whether or not a specific substance you touch, breathe or eat is causing symptoms.

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2 Reasons for Procedure

Here are the most common reasons to undergo an allergy skin test.

Information from an allergy test can direct your doctor to develop an allergy treatment plan that includes avoiding the allergen, medication or allergy shots

Allergy skin tests are widely used to help diagnose allergic conditions including:

A skin test is generally safe for adults and children of all ages, including infants. In certain instances, though skin tests are not recommended.

Your doctor may advise against skin testing if you

Have had a severe reaction

You may show high sensitivity to certain substances that even the tiny amounts used in skin test could initiate a life-threatening reaction (anaphylaxis). Take medications that could interfere with the results. This include:

  • antihistamines
  • most antidepressants
  • and some heartburn medications

Have certain skin conditions

If severe eczema or psoriasis affects large areas of skin in your arms and back, there may not be enough clear, uninvolved skin to do an effective test. Other skin conditions, such as dermatographism, can cause unreliable test conditions.

Blood tests can  be very useful  for those who shouldn't undergo skin tests. Blood tests are not done as often as skin test are because they can be less sensitive than skin tests and more expensive.

Generally, allergy skin tests are the most reliable form of testing for diagnosing allergies to airborne substances, such as:

  • pollen
  • pet dander
  • and dust mites

Skin testing may help diagnose food allergies as well. But because food allergies can be complex, you may need additional tests for procedures.

3 Potential Risks

The potential risk of skin testing for allergy is slightly swollen, red, itchy bumps (wheals).

Wheals may not be noticeable during the test. In some individuals, though, an area of swelling, redness and itching may develop a few hours after the test and persist for a period that can last a couple of days.

Allergy test rarely produces severe, immediate allergic reactions.

It is vital to have skin tests performed at an office where appropriate emergency equipment and medications are present.

4 Preparing for your Procedure

In preparing to make a recommendation of a skin test for allergy, your doctor will ask you detailed questions about your medical history, your signs, and symptoms and your usual way of treating them.

Your answers can help him or she determines if the allergies run in your family and if an allergic reaction is responsible for causing your symptoms.

Yout doctor may also perform a physical exam to search additional clues about the cause of your signs and symptoms.

Before the doctor can schedule a skin test, he or she will ask ou to bring a list of all your prescription and over-the-counter medications. Some medications can:

  • suppress allergic reactions, preventing the skin testing from giving precise results
  • other medications may increase your risk of developing a severe allergic reaction during a test

Medications clear out of for system at different rates, for this reason, your doctor may ask you to stop taking certain medications for up to 10 days.

Medications that can interfere with skin test include:

  • prescription antihistamines
  • over-the-counter antihistamines
  • tricyclic antidepressants (nortripttyline and ranitidine)
  • certain heartburn medications
  • and the asthma medication omalizumab

This medication can disrupt test results for six months or longer even after you stop using it (most medications affect the results from days to weeks).

5 What to Expect

Here’s what you can expect before, during, and after your skin test for allergy.

Skin testing is usually performed at a doctor's office. Generally, a nurse administers the test and the doctor interprets the results.

Typically, this test takes about 20 to 40 minutes. Some tests detect immediate allergic reactions, which develop within minutes of exposure to an allergen. Other tests detect delayed allergic reactions, which develop over a period of several days.

A skin prick test, also known as a puncture or scratch test checks for immediate allergic reactions to as many as 40 diverse substances simultaneously.

This test is performed to determine allergies to:

  • pollen
  • mold
  • pet dander
  • dust mites
  • and foods

In adults, the test is usually done on the forearm. Children may be tested on the upper back. Allergy skin tests are not painful. Needles used to in this type of testing barely penetrate the skin's surface. You will not bleed or feel more than mild, temporary discomfort.

After cleaning the test site with alcohol, the nurse will proceed to draw small marks on your skin and apply a drop of allergen extract next to each mark. He or she then proceeds to use a lancet to prick the extracts into the skin's surface.

A new lancet is used for each allergen. To see if your skin is reacting as it should, two additional substances are scratched into your skin's surface.

These are histamine and glycerin or saline. In most individuals, histamine causes a skin response. If you do not react to histamine, your allergy skin test may not reveal an allergy even if it is present.

Glycerin or saline do not cause any reaction in most people. If you react to glycerin or saline, you may have sensitive skin. About 15 minutes after the skin pricks, the nurse observes your skin for any signs of an allergic reaction. If you are allergic to one of the substances tested, you will develop a raised, red itchy bump that may be similar in appearance to a mosquito bite.

The nurse will then measure the bump size. A skin injection test can also be performed. In this test, a needle is used to inject a small quantity of allergen extract just into the skin on your arm. The injection site is examined after 15 minutes for signs of an allergic reaction. Your doctor may recommend this test to check for an allergy to insect venom or penicillin.

Patch testing can also be performed to see whether a particular substance is causing the allergic reaction. Patch tests can detect delayed allergic reactions, which can take several days to develop. There are no needles used in patch testing, allergens are supplied through patches placed on your skin.

During a patch test, you skin may be exposed to 20 to 30 extracts of substances that can cause contact dermatitis. This may include:

  • latex
  • medications
  • fragrances
  • preservatives
  • hair dyes
  • metals
  • and resins

You wear the patches on your back or arm for 48 hours. Within this period, you should avoid bathing and activities that may cause heavy sweating.

The patches are removed when you return to your doctor's office. The irritated skin at the site of the patch may indicate an allergy.

6 Procedure Results

Understanding the results of your skin test for allergy will be made possible by your doctor.

Before you leave the doctor, you will be made aware of the results of a skin prick test or an intradermal test.

A patch test may test longer to provide results, usually several days or more. A positive skin test means that you may be allergic to a particular substance.

Bigger wheals usually indicate a greater degree of sensitivity. A negative skin test means that you are not allergic to any of the allergens.

It is important to keep in mind that skin tests are not always accurate. They may sometimes indicate an allergy when there is not one (false positive) or the opposite (false negative).

Your allergy treatment plan may include:

  • medications,
  • immunotherapy,
  • changes to your work or home surrounding,
  • or dietary changes.

Ask your doctor to explain anything about your diagnosis or treatment that you do not understand. With test results that identify your allergens and a treatment plan to help you take control, you will be capable of reducing or eliminating the signs and symptoms of allergies.

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