The two main ways to detect allergies are skin and blood testing. Blood allergy testing detects a specific IgE antibody directed at a particular allergen such as pollen, animal dander, or a food. Skin testing is done more frequently because it is generally less expensive and the results are available more quickly (at the same visit during which the testing is performed). In some cases, skin testing may be more likely to detect an existing allergy than blood allergy testing. Advantages of blood allergy testing include the lack of interference from antihistamines (which have to be avoided for several days for skin testing) as well as the greater availability of allergens for testing. In the case of food allergy, it is often important to obtain both skin tests and blood allergy tests.
The interpretation of blood allergy tests is complex. Your BVAAC board-certified allergist must incorporate information from skin testing, as well as your history (e.g. symptoms, age, other allergic illnesses, etc.) to arrive at an optimal management plan. It is important to understand that a positive test does not always mean that a reaction will occur with allergen exposure, and a negative test does not always rule an allergy out.
Allergy blood tests should look only at specific IgE levels. Some “food sensitivity tests” look at specific IgG antibodies. IgG is a different type of antibody that plays no role in allergy and is only a sign of exposure and tolerance. These specific IgG tests are not helpful nor recommended. In fact, the guidelines for clinical practice in our specialty of allergy and immunology recommend strongly that IgG antibodies to allergens should not be obtained. Click here for a handout from the American Academy of Allergy, Asthma and Immunology discussing IgG antibody testing.
Blood allergy tests may be preferred over skin tests under certain circumstances such as the inability of the patient to come off antihistamines, presence of severe rashes that would interfere with the skin test interpretation, etc.
