The results of an immunoglobulin E test are either negative or positive. If the results are negative, then the patient has a normal level of the immunoglobulin E antibody. If the results are positive, then the patient has an elevated level of the antibody, indicating a possible allergic reaction to the substance or group of substances, explains WebMD. Patients typically receive results within seven days of testing.
An immunoglobulin E test uses blood samples to test for the presence of antibodies. These tests are generally less effective and more expensive than skin tests, so some patients may display allergic responses to a skin test but not a blood test, according to WebMD. Doctors may prescribe the blood test for patients who have extreme allergic responses or active skin conditions which already inflame the skin, such as eczema. Blood tests may also be appropriate for patients taking antihistamines or tricyclic antidepressants as these medications can skew the results of a skin test. Doctors also commonly use the tests before surgery to test patients for latex allergies.
Immunoglobulin E tests are the most common allergy blood tests, but there are other tests available, including radioallergosorbent and multiple-antigen simultaneous tests, states WebMD. Enzyme-linked immunosorbent assay blood tests can be particularly effective in diagnosing food allergies in individuals who display positive skin-test results in response to a variety of foods.