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diagnostic procedures and tests
Allergy Testing |
Allergy TestingAllergy testing also referred to as scratch test or patch test is done to detect the allergy-causing substance.
The substance that triggers or stimulates an allergic reaction is called an allergen. Allergic symptoms include itchy nose or eyes, hives, anaphylaxis, wheezing and so on. The causative factor is determined and removed. The most common allergy testing procedures are skin tests, elimination-type tests, and (RAST) radioallergosorbent test.
Allergy and patch testing is the most common diagnostic method. Anti-histamines usage is completely stopped before test commencement. Allergy skin testing method is utilized in checking out suspected allergens. A small quantity of the allergen is intradermally injected and watched for a reaction.
The scratch test technique involves the placement of the suspected allergen on the skin of the fore arm and scratching the area. A spontaneous wheal and flare is noticed within 20 minutes with redness and inflammation. The advantage of this method lies in the fact that, more than one allergen is detected at the same time.
Prick method involves the introduction of the allergen by a puncture. Reaction begins in case of allergy.
Food allergy testing includes, Elimination diets, which, as the name indicates refers to the removal of a suspected food from the diet schedule for a few weeks. The food is reintroduced gradually and the signs of allergy are noticed. Food allergy testing kits are available commercially.
The radioallergosorbent test (RAST) is a lab test which quantifies the Immunoglobulin E (IgE) antibodies in the blood. These are seen in the case of an allergic reaction.
Increased amount of eosinophils can also indicate the presence of allergy. Challenge testing introduces the suspected allergen by oral or inhaled route. This is usually done in the presence of an allergist. The prick plus prick test, is a technique wherein the allergen food is pricked and the sap is collected.
The patient is pricked again with the fresh extract.
ELISA or EIA (Enzyme Immunoassays) is used to detect Immunoglobulin G (IgG) antibodies, as certain subclasses of IgG antibodies is present in response to certain food allergens. A Double blind placebo controlled food challenge test is also followed. But, this method triggers anaphylaxis and is fatal. Serious allergic reactions can be instigated by stings from insects, foods, natural rubber latex and drugs.
Tell your physician about all the nonprescription and prescription drugs you take. Medications such as antidepressants and antihistamines should be stopped before an allergy skin testing. Alcohol or caffeinated beverages is avoided before RAST. Foods and other fluids are not restricted. Though antidepressants and antihistamines have no effect on radioallergosorbent test (RAST) results, a radioactive bone or thyroid scan, a week before the test is not advised.
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