How are allergies identified?
Because people are often allergic to more than one allergen, you will need to have several tests done to identify which ones are causing your allergy. The biggest clue for getting started is the season in which your symptoms occur. Your doctor will use this information to order the first tests.
In most cases, they are skin tests. In this procedure, the doctor places extracts of the allergens on your arm or back and then pricks the skin gently just to break its surface so the extract can enter the outer layer of the skin (epidermis). If you are allergic to the allergen in that extract, the pricked area will become red and itchy.
Sometimes another test is needed to confirm the first test. This involves injecting a small amount of an extract just under the surface of your skin, much like what happens during a tuberculin (TB) test.
Most skin tests take between 15 and 30 minutes, depending on your symptoms and whether second tests are needed. Skin tests are the best and fastest way for identifying the substances to which you might be allergic.
Certain conditions, however, could prevent your doctor from performing skin tests. If these conditions exist, your doctor will perform blood tests instead to check the levels of allergic (IgE) antibodies. Higher levels of certain antibodies can identify particular allergies. Because the blood test is not as sensitive as the skin tests, most doctors use it only when they have no other choice.