Allergy Skin Tests

During an allergy skin test, your skin is exposed to allergy-causing substances (allergens) and then is observed for signs of a local allergic reaction.

Along with your medical history, allergy tests can confirm whether signs and symptoms, such as sneezing, wheezing and skin rashes, are caused by allergies.  Allergy tests can also identify the specific substances that trigger allergic reactions.

Why it’s done

Allergy skin testing is widely used to diagnose allergic conditions such as:

  • Hay Fever
  • Allergic asthma
  • Dermatitis (eczema)
  • Food allergies
  • Penicillin allergy
  • Bee Sting allergy

Skin testing can be used for people of all ages.  Your doctor may advise against skin testing if you:

  • Take medications that interfere with test results.  These include antihistamines, many antidepressants and some heartburn medications.  Your doctor may determine that it’s better for you to continue taking these medications than to temporarily discontinue them in preparation for a test.
  • Have a severe skin disease.  If conditions such as eczema or psoriasis affect large areas of skin on your arms and back-the usual testing sites-there may not be enough clear, uninvolved skin to do an effective test.
  • Are highly sensitive to suspected allergens.  You may be so sensitive to certain substances that even the small amounts of them used in skin tests could trigger a severe allergic reaction (anaphylaxis).

Risks
The most common side effect of skin testing is slightly swollen, red, itchy bumps (hives).  Hives may be most noticeable during the test.  They usually go away with a few hours, although they can persist for a day or two.  A mild cortisone cream can be applied to relieve the itching and redness.

How you prepare

Before recommending a skin test, your doctor will ask detailed questions about your medical history, your signs and symptoms, and your usual way of treating them.  There is no prep involved for skin testing.

Medications can interfere with results

Before scheduling a skin test, you will need to provide us with a list of all your prescriptions and over-the-counter medications.  Some medications can suppress allergic reactions, preventing the skin testing from working effectively.  Other medications may increase your risk of developing a severe allergic reaction during a test.
Because medications clear out of your system at different rates, your doctor may ask that you stop certain medications for up to 10 days.  Medications that can interfere with skin tests include:

  • Prescription nonsedating antihistamines, such as fexofenadine (Allegra).
  • Over-the-counter antihistamines (Claritin, Benadryl, Chlor-Trimeton, Zyrtec)/
  • Heartburn medications, such as cimetidine (Tagament) and ranitidine (Zantac).

What you can expect
Allergy skin tests aren’t painful.  Because the needles used in these tests barely penetrate your skin’s surface, you won’t bleed or feel more than mild, momentary discomfort.

During the test

We do a percutaneous skin test.  In this test, which is the most common type of skin test, tiny drops of purified allergen extracts are pricked or scratched into your skin’s surface.  Tests detect immediate allergic reactions, which develop within minuets of exposure to an allergen.

We perform a battery of allergic allergens usually 40 different substances at one time.

To see if your skin is reacting the way it’s supposed to, the technician will prick your arm first with a histamine.  In almost everyone, this substance causes a skin response, so it’s used as a positive control.  If you don’t react to histamine, the skin test may be difficult or impossible to interpret.

After, cleaning the test site with alcohol, we apply a drop of allergen extract the technician will number the spot on your back where test was applied.  The drops are left on your skin for 20 minutes, and then the technician observes your skin for signs of allergic reactions.

After the test
If an allergen causes an allergic reaction to a puncture skin test, you’ll develop a raised, red, itchy bump that may look like a mosquito bite.  The technician will then measure the bump’s size.

Results

Before you leave the office you will know the results of your test.

A positive skin test means that you may be allergic to a particular substance.  Bigger bumps usually indicate a greater degree of sensitivity.  A negative skin test means that you probably aren’t allergic to that particular allergen.

The accuracy of skin tests can vary.  You may react differently to the same test performed at different times.  Or you may react positively to a substance during a test but not react to it in everyday life.

In general, skin tests are most reliable for diagnosing allergies to airborne substances, such as pollen, pet dander and dust mites.

Your allergy treatment plan may include medications, immunotherapy (Xolair), and environmental changes.  With test results that identify your allergens and a treatment plan to help take control, you’ll be able to reduce or eliminate allergy signs and symptoms.

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