Skin testing helps diagnose allergies and disease
A skin test may be used to check for allergies or to help diagnose disease such as tuberculosis or skin cancer. There are a variety of skin tests, depending on what your doctor is trying to determine, and they’re usually conducted in a doctor’s office. Skin tests are generally painless but may cause mild discomfort if you do have a reaction such as redness or itchiness, or if you have a skin injection or biopsy, you may have some tenderness after the local anesthesia (numbing agent) has worn off.
Types of skin tests
The main types of skin tests are:
- Skin prick test – also known as a scratch test, this involves gentle needle scratches on the skin (usually the forearm) and dropping a small amount of allergen on the open skin. This method usually produces a skin reaction, an itchy, raised bump called a wheal, within 15 minutes.
- Skin injection test – when an allergen such as from a bee sting or medication like penicillin is injected into the arm, usually producing a reaction within about 15 minutes. It is also commonly used with tuberculin purified protein (PPD) to detect for presence of tuberculosis.
- Patch test – used to test for contact dermatitis (skin reaction/allergy). Instead of needles, patches with the allergens such as latex, hair dyes, metals and fragrances, are placed on the skin of the back or the arm. The reaction may be delayed up to 48 hours.
- Skin biopsy – a skin test used specifically to identify cancerous cells in the skin. The procedure involves scraping or removal of skin cells to be sent to a laboratory for study and to determine whether the cells are benign or malignant.
- Physical exam – a thorough examination of the body by a skilled dermatologist who will check for the presence of bumps, lumps, moles and skin abnormalities to determine whether certain skin samples should be tested for the presence of skin cancer.
Results from skin testing
For allergy tests such as the skin prick test and skin injection test, you will likely find out the results of your test right away. A skilled allergist may be hesitant to diagnose you with allergies, however, as sometimes skin testing can produce false-positives, which is indication that you have an allergy when in fact you do not have one. Additional testing may be recommended.
For patch tests you will return to the allergist’s office to have the patches removed after 48 hours so the doctor can determine whether the patches caused any reaction. If you have had reaction to any of the skin testing, your doctor will advise you on how to proceed.
Skin biopsy results are generally available within one to two days. If your doctor has found skin cancer, he or she will discuss your options with you and together you can determine next steps.