There are several types of specific allergy tests. There are skin and blood tests for allergies.
Immediate-type hypersensitivity (IgE) SKIN PRICK TESTS are typically used to test for airborne allergens like pollen, dust mites or fungus, foods, insect stings, and penicillin. Immediate-type hypersensitivity also can be evaluated through serum IgE antibody testing called IMMUNOCAP testing or radioallergosorbent testing (RAST).
Delayed-type hypersensitivity skin tests (patch-type skin tests) are commonly used in patients with suspected contact dermatitis. Some common allergens for patch testing are rubber, medications, fragrances, vehicles or preservatives, hair dyes, metals, and resins.
Skin tests are used most of the time. There are three main kinds of skin tests. The first kind is called a "prick" test. Positive-control skin tests (histamine) and negative-control skin tests (diluent) are essential for correct interpretation of skin test reactions. A tiny drop of testing allergen fluid is placed on your skin. Then, the skin is pricked through the drop. About 15 minutes after the application of the allergen to the skin, the test site is examined for a wheal and flare reaction. A positive skin test reaction (typically, a wheal 3 mm greater in diameter than the negative control reaction, accompanied by surrounding erythema) reflects the presence of mast cell -bound IgE specific to the tested allergen.
There's a "prick" sensation when the testing is applied, but it is not painful. The doctor chooses the allergens, and upto 200 prick tests may be needed for a full exam. The skin prick test is still the GOLD STANDARD for allergy testing.
Intra-dermal Tests: In the second kind of skin test, the testing fluid is injected into your skin (like a shot). This test is used to check for allergy to medicines (most often penicillin) and bee-sting allergy.
The third kind of skin test is called a patch test. A small patch of material soaked in testing fluid is taped on your skin. After 2 or 3 days, your doctor will take off the patch and look for redness and swelling in your skin. Patch tests are used to evaluate rashes caused by allergy to things that might rub against your skin.
Some commonly used medicines, like pain killers and antihistamines, can interfere with skin tests. If you take these medicines, you have to stop taking them before skin tests can be done. Antihistamines interfere with the development of the wheel and flare reaction and should be stopped before immediate-type skin testing. First-generation antihistamines may be stopped two to three days before testing, but the newer, second-generation antihistamines can affect skin testing results for a minimum of 3 days. Medications with antihistamine properties, such as anticholinergic agents, phenothiazine, and tricyclic antidepressants, also should be discontinued before skin testing. Histamine H2-receptor antagonists (Antacids like Zinetac) have a limited inhibitory effect; these medications may be stopped on the day of skin testing. Systemic corticosteroids nasal sprays and inhalers generally do not significantly suppress the wheal and flare reaction of immediate-type skin tests. Oral steroids should be stopped 3 days before skin prick tests.