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Allergy Diagnosis

 

Allergy diagnosis is a multistep process involving physical exam, health history and allergy testing.

If allergies are suspected, your allergist will ask you about your health , family history, environment and perform a physical exam. He or she will ask you to fill out a questionnaire about your symptoms to determine what type of symptoms you have, their severity and where and when they occur.  Your allergist may perform allergy tests to determine what you are allergic to and how severe the allergy is. These tests include skin testing (prick technique and intradermal), challenge testing, Immunocap blood testing for specific IgE or immunology blood tests, and patch testing.

Skin Test Via the Skin Prick Technique

This allergy skin test involves having a drop of a suspected allergen pricked on the surface of the skin. The test is performed on the back or forearm and many suspected allergens are tested at the same time.  Allergens that are commonly tested include: dust mites, pet proteins, mold, pollen, insect venom, foods, latex and medications.   If you have an allergy to one of the substances tested,  redness and swelling will begin to appear at that test spot.  Typically, positive reactions will appear within 15 minutes and go away within 30 minutes. However, sometimes redness and swelling can occur several hours after skin testing. The delayed reaction usually disappears in 24 to 48 hours, but should be reported to your allergy doctor or nurse.

This skin test causes very little or no pain; however, positive reactions can cause annoying itching and redness at the test site. The itching can last few short minutes or hours.

Skin Test Via Intradermal Allergy Test

In this allergy skin test, a small amount of the suspected allergen is injected under the skin of the arm or forearm. This skin allergy test is more sensitive than the prick test and can be used when a prick test comes back negative, but allergies are still suspected.  Much like the prick test, several suspected allergens are tested at the same time. Again, if you have an allergy to one of the substances tested, redness and swelling will begin to appear at that test spot.  The intradermal skin test is very similar to the prick test in that  positive reactions will appear within 15 minutes; however, sometimes redness and swelling can occur several hours after skin testing. The delayed reaction usually disappears in 24 to 48 hours, but should be reported to your allergy doctor or nurse.

The following medications interfere with skin allergy testing; therefore, we ask that you discontinue the following medications for three days prior to your initial visit and any subsequent skin testing visits:

  1. All antihistamines including Actifed, Alavert, Allegra, Allegra-D, Atarax,  Benadryl, Bromfed, Claritin, Cetirizine, Chlortrimeton, Claritin, Claritin-D, Deconamine, Dimetapp, Diphenhydramine HCl, Doxepin, Duradryl, Extendryl, Fexofenadine, Hydroxyzine, Kronofed-A, Levocetirizine Loratadine, PediaCare, Phenergan, Promethazine,  Rondec, Rynatan, Semprex-D, Tavist,  Triaminic, Vistaril, , Xyzal, Zyrtec and Zyrtec-D.
  2. Astelin, Astepro, and Patanase nasal sprays
  3. Over the counter sleep aids such as Tylenol PM which contains Diphenhydramine(Benadryl).

Do not stop Singulair

Discontinue Clarinex for five days prior to your initial visit and any subsequent skin testing.

If you are  experiencing active hives, continue all medications. We urge you to keep any scheduled appointment even if you continue to take an antihistamine during those three days.  You should continue to take all asthma medications, including oral inhalers.  If you have any questions about a specific medication not mentioned, please call the office.

Challenge Testing

Challenge testing involves introducing suspected allergens by oral,  inhaled or injection routes under the close supervision of your allergy doctor.  This type of testing is usually performed for suspected food and medication allergies.

Blood (RAST) Test

Blood (Immunocap) Test

Immunocap for specific IgE is an allergy blood test that is often used under the following conditions:

  • A patient is taking a medication that can interfere with skin testing and cannot be stopped for a few days.
  • A patient suffers from a severe skin condition such as eczema or psoriasis.
  • Testing with a strong allergen might cause an extra large positive reaction.
  • The patient is a baby or very young child and a single needle stick for allergy blood testing may be better tolerated than several skin tests.

Because the blood sample must be sent to a lab for testing, it takes 2 to 3 weeks to get the results. These tests are not as sensitive as IgE prick tests and a negative result does not exclude an allergy.

Patch Testing

Patch testing is used for patients who have chronic, recurring contact dermatitis. It requires three office visits over five days. On the first visit, small patches of potential allergens are applied to the skin. These patches are removed 48 hours later to see if a reaction has occurred. A third visit approximately 2 days later is to evaluate for any delayed reaction. You should bring suspected materials with you, especially if you have already tested those materials on a small area of your skin and noticed a reaction.

If you are scheduled for patch testing, please discontinue oral and topical steroids. Antihistamines may be continued.

Each test method has benefits and drawbacks. The test results alone do not diagnose allergies.  All test results must be interpreted together with the medical history.

 

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