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Allergy Testing

Allergy TestAllergy skin testing

Allergy skin testing is widely used to identify triggers in conditions such as:   * Hay fever * Allergic asthma * Dermatitis (eczema) * Food allergies * Penicillin allergy * Insect sting allergy.

Skin testing can be used for people of all ages, including infants and older adults.

Before recommending a skin test, Dr. Druce will ask detailed questions about your medical history, your signs and symptoms, and your usual way of treating them. Your answers can help you doctor determine in allergies run in your family and if you might also have them. Next, Dr. Druce will perform a physical examination to search for additional clues about the causes of your signs and symptoms. Your medical history and physical examination may provide enough information for your doctor to discuss your diagnosis and treatment. If so, a skin test may be unnecessary. But if information about the possible causes, he may recommend that you have a skin test.

You might not be able to have the skin test on the same day of our first visit, because:

Medications Can Interfere with Skin Test Results

Medications can interfere with skin test results. Dr. Druce will need a list of all your prescription 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, Dr. Druce may ask that you stop taking certain medications for up to 10 days. Medications that can interfere with skin tests include:

  • Non-sedating antihistamines, such as fexofenadine (Allegra), loratadine (Claritin), diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), cetirizine (Zyrtec) and others.
  • Tricyclic antidepressants such as amitriptyline and doxepin (Sinequan).
  • Any medication with a “PM” or “Nighttime” in the name (contains antihistamines).

Skin testing is performed in the doctor’s office. Allergy skin tests aren’t painful. Dr. Druce does not use needles for initial routine testing. Because the plastic brushes used in these tests barely penetrate your skin’s surface, you won’t bleed or feel more than mild momentary discomfort. The test method used by Dr. Druce uses the most comfortable test applicators available.

What to expect during the test.

There are three main types of skin tests:

  • Puncture, prick or scratch test (percutaneous). In this test, which is the most common type of of skin test, tiny drops of purified allergen extracts are pricked or scratched into your skin’s surface. This test is usually performed to identify allergies to pollen, mold, pet dander, dust mites and foods. Dr. Druce uses the plastic applicators and brushes for this.
  • Intradermal test (intracutaneous). Purified allergen extracts are injected into the skin of your arm.
  • Patch test (epicutaneous). This test doesn’t use needles. Instead, an allergen is applied to a patch, which is then placed on your skin. This test is usually performed to identify substances that cause contact dematitis. These include latex,  medications, fragrances, preservatives, hair dyes, metals and resins. Some tests detect immediate allergic reactions, which develop within minutes of exposure to an allergen. Other tests detect related allergic reactions, which develop over a period of several days.

Tests for Immediate Allergic Reactions

A puncture, prick or scratch test checks for immediate allergic reactions to as many as 60 different substances at one time. After cleaning the test site with alcohol, Dr. Druce applies 10 tests at a time with the plastic applicator. The drops are left on your skin for 10 minutes and then Dr. Druce observes your skin for signs of allergic reactions. To see if your skin is reacting the way it’s supposed to, Dr. Druce introduces two additional substances into your skin’s surface:

  • 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.
  • Saline. In almost everyone, this substance causes no reaction. So this is used as a negative control. If you react to saline, you may have sensitive skin, so your reactions to the allergen extracts will need to be interpreted with caution.

Intradermal Tests

You may need a more sensitive immediate reaction test known as an intradermal test. If a puncture, prick or scratch test is inconclusive. During this test, Dr. Druce uses a thin needle and syringe to inject a small amount of allergen extract just below the surface of the skin on your arm. Then he inspects the site after 15 minutes for a local skin reaction.


Sometimes, however, skin tests aren’t recommended. Dr. Druce 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 reactions (anaphylaxis). Blood tests, technically called in vitro allergen-specific IgE antibody tests are, are particularly useful for those who shouldn’t undergo skin tests.

Side Effects

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 within 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.

If you develop a severe allergic reaction in the days after a skin test, call Dr. Druce right away, or after the office is closed go directly to your nearest emergency room.

After the Test

If an allergen causes an allergic reaction to a puncture or intradermal skin test, you’ll develop a raised, red itchy bump that looks like a mosquito bite. Dr. Druce will measure the bump’s size. After he records the results, he will clean your skin with alcohol to remove the marks and allergen droplets. Then you’ll discuss the results and possible treatment options.


Before you leave Dr. Druce’s office, you’ll know the results of a puncture, prick or scratch 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 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. Because diagnosing food allergies can be complex, you may need additional tests or procedures.

Blood testBlood Tests

Although blood tests can be as accurate as skin tests, they’re not performed as often because they can be less sensitive and are more expensive. If you want to start immunotherapy, which is a series of injections intended to increase your tolerance to allergens, you need either a skin or blood test to identify the specific substances that trigger your allergies.

Your allergy treatment plan may include medications, immunotherapy, environmental changes or dietary changes. Ask Dr. Druce 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.