The two main ways to detect allergies are skin testing and blood allergy testing. Blood allergy testing detects a specific IgE antibody directed at a specific allergen such as grass, cat, or peanut, etc. Skin testing is done more frequently because it is generally less expensive and the results are available more quickly. In many 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 Advantages of blood allergy testing include the lack of interference from antihistamines (which have to be withdrawn for skin testing) as well as the greater availability of allergens for testing.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.
Their interpretation of blood allergy tests is complex. Your BVAAC board-certified allergist must incorporate information from skin testing, as well as the patient’s history (e.g. symptoms, age, other allergic illnesses, etc.) to arrive at an optimal management plan). It is important to emphasize 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.
It is important to emphasize that we obtain blood allergy tests to specific IgE antibodies. Blood allergy test to specific IgG and IgG subclass antibodies only represent exposure, not true allergy, and are not useful. In fact, the guidelines for clinical practice in our specialty of allergy and immunology recommend strongly that IgG and IgG subclass antibodies to allergens should not be obtained because they are not helpful. Click here for a handout from the American Academy of Allergy, Asthma and Immunology discussing IgG antibody testing.
Blood allergy tests may be obtained under certain circumstances: inability of the patient to come off antihistamine, severe skin rash, unclear clinical situation, food allergy, etc.
