Allergy Test

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• QWhat is ImmunoCAP ISAC?

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  A Dr. Paul M. Ehrlich, MD , Allergy & Immunology, answered

  ImmunoCAP (Immuno Solid-phase Allergy Chip) ISAC is the latest thing in allergy testing. Developed by VBC Genomics and Phadia, ImmunoCAP uses specific molecular components of allergens. Conventional testing uses are based on allergen prepared from biological raw materials, which contain mixtures of allergenic and non-allergenic molecules. They can't be fully standardized according to major or minor allergen components, which may account for some of the false positives we see in radioallergosorbent (RAST) testing.
  
  The number of components ImmunoCAP can test for now is limited but growing. The big test will come when we see if it leads to more precise therapies. However, one advantage to anxious parents and children is that it involved only a fingertip prick instead of blood drawing or skin scratching.
• QWhat is allergy skin testing?

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  A Dr. Scott H. Sicherer, MD , Pediatrics, answered on behalf of The Mount Sinai Health System

  This is a simple test that can be done with minimal discomfort and provides an allergist with a quick answer about whether your body is responding to an allergen, whether it is a pollen, animal dander, mold, food or other allergen. In general, an extract of the protein is introduced into the top edge of the skin on the arm or back with a plastic or metal device that makes a scratch (no bleeding). If your body has recognized the tested item as a possible allergen, a small itchy spot, like a mosquito bite, develops in 10-15 minutes right where the test was done. The allergist also uses a negative comparison and a positive comparison test. The main limitation of the test is that it can be positive in a person that may not have any symptoms when they are exposed to what was tested. That is why the allergist must do a complete history prior to any testing, to consider if your symptoms are allergic, what may be triggering them, and then decide upon what should be tested and how to then interpret those test results. This test (and similar allergy blood tests) can be very misleading if they are done to “screen” for allergy without considering the illness under consideration, exposures and their relationship. In some cases, the allergen being tested is injected under the skin with a small needle, but this manner of skin test is usually reserved for special situations and the allergy scratch test (also called prick test) is more often used.

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• QWhat is a radioallergosorbent (RAST) blood test?

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  A RealAge answered

  A RAST (radioallergosorbent) blood test looks for specific immunoglobulin E (IgE) antibodies in your blood. If the antibodies are present, it most likely indicates a true allergic reaction. RAST is the safest type of allergy test, but compared with a skin prick test, it takes longer to produce results and it can't test for as many allergens at once.
  
  This type of allergy test is typically used only in special circumstances where skin testing is not advised -- for example, if a person has a severe skin condition or is taking certain medications.

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