One of the common causes of smell disturbances is nasal allergy (Allergic Rhinitis), particularly when accompanied by nasal polyps or infection in the sinuses. In order to determine whether allergy is the cause of the smell disturbance, allergy testing is routinely performed. It is estimated that greater than 20 percent of smell disturbances involves nasal allergy or infection of the sinuses.
Allergy testing involves having a skin or blood test to find out what substance, or allergen, may trigger an allergic response in a person. Skin tests or blood tests are usually done and both are reliable.
A small amount of a suspected allergen is placed on or below the skin to see if a reaction develops. There are three types of skin tests:
Skin prick test. This test is done by placing a drop of a solution containing a possible allergen on the skin, and a series of scratches or needle pricks allows the solution to enter the skin. If the skin develops a red, raised itchy area (called a wheal), it usually means that the person is allergic to that allergen. This is called a positive reaction.
Intradermal test. During this test, a small amount of the allergen solution is injected into the skin. An intradermal allergy test may be done when a substance does not cause a reaction in the skin prick test but is still suspected as an allergen for that person. The intradermal test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen (false-positive test results).
Skin patch test. For a skin patch test, the allergen solution is placed on a pad that is taped to the skin for 24 to 72 hours. This test is used to detect a skin allergy called contact dermatitis.
Allergy blood tests look for substances in the blood called antibodies. The most common type of blood test used is the enzyme-linked immunosorbent assay (ELISA, EIA). It measures the blood level of a type of antibody (called immunoglobulin E, or IgE) that the body may make in response to certain allergens. IgE levels are often higher in people who have allergies.