A skin test is a medical procedure used to identify allergies or infections by introducing a small amount of allergen or antigen into the skin. The body's reaction is then observed to determine the presence and severity of a reaction. This is a common and relatively quick method for diagnosing various conditions.
Types of Skin Tests
There are several types of skin tests, each designed for different purposes:
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Skin Prick Test (Scratch Test): This is the most common type. A tiny amount of allergen is placed on the skin, then a small scratch or prick is made, allowing the allergen to enter the skin's surface. The reaction is observed within 15-20 minutes. This test can check for reactions to many substances simultaneously. [Reference: Mayo Clinic, Nemours KidsHealth, Cleveland Clinic]
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Intradermal Test: A small amount of allergen is injected just beneath the skin's surface. This method is more sensitive than the skin prick test but also carries a slightly higher risk of a more significant reaction. [Reference: Cleveland Clinic, Mount Sinai]
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Patch Test: Used to detect delayed-type hypersensitivity reactions, such as contact dermatitis. A small amount of allergen is applied to the skin under a patch, left for 48 hours, and then checked for reactions. [Reference: MedlinePlus, Cleveland Clinic]
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Tuberculin Skin Test (TST): This test is specifically used to check for exposure to Mycobacterium tuberculosis, the bacteria that cause tuberculosis (TB). A small amount of tuberculin is injected under the skin, and the reaction is checked after 48-72 hours. A two-step test can help distinguish between old and new infections. [Reference: CDC, MN Dept. of Health]
Interpreting Results
The interpretation of skin test results varies depending on the type of test and the substance tested for. A positive reaction usually indicates an allergy or prior exposure to the tested substance, manifested as a wheal (raised bump), redness, or other signs of inflammation. The size and appearance of the reaction are important factors in determining the severity. It's crucial to remember that skin test results, alone, do not diagnose allergies. A healthcare professional will interpret the results in conjunction with a patient's medical history and other factors. [Reference: ACAAI Patient]
