In vitro specific allergy testing is an alternative technique for specific allergen testing. In vitro testing encompasses several types of testing, including total IgE testing, serum-specific IgE assays, and the Basophil Activation Test (BAT). The testing has unique advantages compared to skin testing. It can safely be used in patients with a history of anaphylaxis or severe asthma without risk of inducing an allergic reaction as no allergen is introduced to the patient. It can be utilized in patients for whom skin conditions preclude skin testing, such as eczema or dermatographism. In vitro testing does not require patients to stop medications that interfere with a skin response prior to testing, such as antihistamines, and can be utilized in testing patients with a relative contraindication to testing, such as those on beta-blockers. A positive test result with serum-specific IgE assays indicates the presence of circulating allergen-specific IgE. Results are delayed compared to skin testing, which has a near-immediate response, and the cost of testing can be variable. Allergen-specific immunotherapy can be prescribed based on the results of in vitro testing and used for desensitization.