Allergy skin tests
Allergy skin tests
During allergy skin tests, your skin is exposed to suspected allergy-causing substances (allergens) and is then observed for signs of an allergic reaction.
Along with your medical history, allergy tests may be able to confirm whether or not a particular substance you touch, breathe or eat is causing symptoms.
Why it's done
Information from allergy tests may help your doctor develop an allergy treatment plan that includes allergen avoidance, medications or allergy shots (immunotherapy).
Allergy skin tests are widely used to help diagnose allergic conditions, including:
Skin testing can be used for people of all ages, including infants. Sometimes, however, skin tests aren't recommended. Your doctor may advise against skin testing if you:
Blood tests (in vitro IgE antibody tests) can be useful for those who shouldn't undergo skin tests. Blood tests aren't done as often as skin tests because they can be less sensitive than skin tests and are more expensive.
In general, allergy skin tests are most reliable for diagnosing allergies to airborne substances, such as pollen, pet dander and dust mites. Skin testing may help diagnose food allergies. But, because food allergies can be complex, you may need additional tests or procedures.
The most common side effect of skin testing is slightly swollen, red, itchy bumps (wheals). These wheals may be most noticeable during the test. They usually go away within a few hours, although they can persist for a day or two. A mild cortisone cream can help ease the itching and redness.
Rarely, allergy skin tests can produce a severe, immediate allergic reaction, so it's important to have skin tests performed at an office where appropriate emergency equipment and medications are available. If you develop a severe allergic reaction in the days after a skin test, call your doctor right away.
How you prepare
Before recommending a skin test, 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 your doctor determine if allergies run in your family and if an allergic reaction is most likely causing your symptoms. Your doctor may also perform a physical examination to search for additional clues about the cause of your signs and symptoms.
Medications can interfere with results
Because medications clear out of your system at different rates, your doctor may ask that you stop taking certain medications for up to 10 days. Medications that can interfere with skin tests include:
What you can expect
Skin testing is usually done at a doctor's office. A nurse generally administers the test and a 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.
Skin prick test
Allergy skin tests aren't painful. This type of testing uses needles (lancets) that barely penetrate the skin's surface. You won't bleed or feel more than mild, momentary discomfort.
After cleaning the test site with alcohol, the nurse draws small marks on your skin and applies a drop of allergen extract next to each mark. He or she then uses 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 normally, two additional substances are scratched into your skin's surface:
About 15 minutes after the skin pricks, the nurse observes your skin for signs of allergic reactions. If you are allergic to one of the substances tested, you'll develop a raised, red, itchy bump (wheal) that may look like a mosquito bite. A nurse will then measure the bump's size.
After the nurse records the results, he or she will clean your skin with alcohol to remove the marks.
Skin injection test
You wear the patches on your arm or back for 48 hours. During this time, you should avoid bathing and activities that cause heavy sweating. The patches are removed when you return to your doctor's office. Irritated skin at the patch site may indicate an allergy.
Positive reaction to allergy test
A small area of swelling with surrounding redness is typical of a positive patch skin test for allergy. ...
Before you leave your doctor's office, you'll know the results of a skin prick test or an intradermal test. A patch test may take several days or more to produce results.
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 probably aren't allergic to a particular allergen.
Keep in mind, skin tests aren't always accurate. They sometimes indicate an allergy when there isn't one (false positive) or skin testing may not trigger a reaction when you're exposed to something that you are allergic to (false negative). You may react differently to the same test performed on different occasions. Or, you may react positively to a substance during a test but not react to it in everyday life.
Your allergy treatment plan may include medications, immunotherapy, changes to your work or home environment or dietary changes. Ask your doctor to explain anything about your diagnosis or treatment that you don't understand. With test results that identify your allergens and a treatment plan to help you take control, you'll be able to reduce or eliminate allergy signs and symptoms.
Last Updated: 2011-04-01
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