Contact dermatitis, respiratory distress and digestive upset are frequent symptoms of an allergic reaction to environmental substances known as allergens. According to the American Academy of Allergy Asthma & Immunology, the most frequent causes of allergies are dust mites, animal dander and saliva, molds, and plant pollen. More serious and potentially serious allergic reactions can result from certain foods, medications and insect stings. When the cause of an allergic reaction is not identified, recurrent exposures to the allergen can trigger a life-threatening immune response called anafilaksis. That's why it is important to test for allergens.
Skin Tests
Scratch tests and patch tests are the most common types of skin tests used to determine the source of an unknown allergen, according to Medline Plus. If the body is sensitive to a specific substance—such as food, mold, penicillin or an inhalant—a slight rash or swelling will appear on the surface of the skin. When a scratch test is employed, a small sample of the suspected irritant is placed on the broken surface of the skin, and the skin is lightly scratched or pricked to allow the substance to go under the skin’s surface. Symptoms of a reaction response will normally appear within an hour. A patch test is frequently used to test for substances that cause contact dermatitis. The potential allergen is placed directly on the skin for 48 hours. Unless a specific allergen is suspected, several substances are frequently tested at one time. An intradermal injection beneath the surface of the skin may be used to confirm uncertain results.
Food Tests
When food allergies are suspected, the health care provider may suggest the patient keep a detailed food diary to help determine the substance and circumstances surrounding the allergic response. An elimination diet requires the patient to remove one food from the diet at a time. If the allergic symptoms go away, the suspected allergen is re-introduced to the diet to see if a reaction occurs once again. A double-blind test hides the identity of the substances tested to prevent the physician and test subject from knowing which product is harmless or the suspected allergen. The National Institute of Allergy and Infectious Diseases warns elimination diets and double-blind tests may be dangerous if the patient has a history of severe allergic reactions.
Blood Tests
Although more expensive than skin tests, blood tests may be a safer approach if a skin test might provoke a severe reaction, according to the Mayo Clinic. The Radioallergosorbent Test, or RAST, is used to measure the amount of IgE antibodies present in the blood stream when the body is exposed to an allergen.
