immune disorders
Overview of Allergic Reactions
Diagnosis of Allergic Reactions
A doctor's evaluation Sometimes blood tests Often skin tests and the allergen-specific serum IgE test Doctors first determine whether a reaction is allergic. They may ask Whether the person has close relatives with allergies because a reaction is more likely to be allergic in such cases How often reactions occur and how long they last How old the person was when the reactions started Whether anything (such as exercise or exposure to pollen, animals, or dust) triggers the reaction Whether any treatments have been tried and, if so, how the person responded To help determine whether a reaction is allergic, doctors sometimes do blood tests to detect a type of white blood cell called Eosinophilic Disorders . Eosinophils, although present in everyone, are usually produced in greater numbers when an allergic reaction occurs. However, the usefulness of this test is limited because other If it seems likely that a person's symptoms are caused by an allergy, the main goal is to identify the specific allergen. Often, the person and doctor can identify the allergen, or at least the type of allergen, based on when the allergy started and when and how often the reaction occurs (for example, during certain seasons or after eating certain foods). Skin tests and a blood test called the Allergen-specific serum IgE tests can also help doctors detect the specific allergen. However, these tests may not detect all allergies, and they sometimes indicate that people are allergic to an allergen when they are not (called a false-positive result). Skin Tests are the most useful way to identify specific allergens. An allergen applied to or injected into the skin should cause a skin reaction in people who are allergic to it. There are two types of skin tests: Skin prick test Intradermal test To help ensure that the results of these skin test are reliable, doctors give two control solutions in addition to the test solution (which contains the suspected allergen). The control substances are A drop of a histamine solution, which should trigger an allergic reaction in anyone, is given. If there is no skin reaction, it may be because the immune system is not working normally or because people have allergy drugs in their system. People who do not react to histamine probably will not react to the test solution that contains the allergen. Thus, people may appear to have no allergy to the allergen when they do (a false-negative result). A drop of diluting solution that contains no allergens and thus should not trigger an allergic reaction is given. If people react to the diluting solution, they probably have sensitive skin, and probably will also react to the test solution that contains the allergen, even if they are not allergic to it (a false-positive result). Usually, doctors give several test solutions. These are dilute solutions, each with one specific antigen. Commonly used antigens include pollens (of trees, grasses, or weeds), molds, dust mites, animal dander, insect venom, foods, or some antibiotics. Doctors choose the antigens for this test based on which substances they suspect to be the cause. Usually, askin prick testis done first. A drop of each of the control and test solutions is placed on the person’s skin, which is then pricked with a needle through the drop. The skin prick test can identify most allergens. If no allergen is identified, anintradermal testmay be done. For this test, a tiny amount of each of the control and test solutions is injected into the person’s skin through a needle. This type of skin test is more sensitive and more likely to detect a reaction to an allergen. If the person is allergic to one or more of the allergens in the test solution, the person has a wheal and flare reaction, indicated by the following: A pale, slightly elevated swelling—the wheal—appears at the pinprick site within 15 to 20 minutes. The resulting wheal is about 1/8 to 2/10 inch (about 0.3 to 0.5 centimeters) larger in diameter than the wheal caused by the diluting solution. The wheal is surrounded by a well-defined red area—the flare. Before skin tests are done, people are asked to stop taking drugs that may suppress a reaction in a person who actually has an allergy to allergens in the test solution. These drugs include Antihistamines Certain antidepressants called tricyclic antidepressants (such asamitriptyline) Omalizumab(a monoclonal antibody manufactured to block IgE) Monoamine oxidase inhibitors (such asselegiline) Some doctors also do not test people who are taking beta-blockers because if such people have an allergic reaction in response to the test, the consequences are more likely to be serious. In addition, beta-blockers may interfere with the drugs used to treat serious allergic reactions. The allergen-specific serum IgE test, a blood test, is used when skin tests cannot be used—for example, when a rash is widespread. This test determines whether IgE in the person's blood binds to the specific allergen used for the test. If binding occurs, the person has an allergy to that allergen. For provocative testing people are directly exposed to a small amount of the suspected allergen. This test is usually done when people must document their allergic reaction—for example, for a disability claim. It is sometimes used to diagnose a Food Allergy . If doctors suspect an 