Diagnostic Tests for Allergy in Children

These tests will help you and your child's healthcare provider or allergist know what substances cause your child's allergy symptoms. Knowing what substances cause the symptoms tells you what your child should stay away from. It also tells the provider what treatments might reduce symptoms. Diagnostic tests for allergy may include:

• Skin tests. These tests measure your child's level of IgE antibody response to certain allergens or triggers. They use small amounts of solutions that contain different allergens. The healthcare provider may give your child a shot (injection) of the solution under the skin. Or the provider may apply the allergens with a small scratch. A reaction would appear as a small red area. A reaction to the skin test does not always mean your child is allergic to the allergen that caused the reaction. This will be determined by your child's provider. Skin testing may not be done on children who have had a severe life-threatening reaction to an allergen. Or children who have severe dry skin (eczema).

• Blood tests. These tests measure IgE antibodies to certain allergens in the blood. The blood test most often used is called RAST (radioallergosorbent test). Or a newer blood test called an ELISA ( enzyme-linked immunosorbent assay) may be done. Blood tests may be used when skin tests can't be done. As with skin testing, a positive blood test does not always mean your child is allergic to that allergen.

• Challenge test. This test is supervised by an allergist. He or she gives your child a very small amount of an allergen. It may be breathed in (inhaled) or taken by mouth (oral).

• Nasal smears. These tests check the amount of eosinophils in the nose. An eosinophil is a type of white blood cell that increases in number during an allergic reaction.