Immunoglobulin E (IgE) is an antibody produced by the immune system in response to some factor or agent that the body perceives as a threat. IgE is one of the five types of immunoglobulins (A, G, M, D and E). Normally, its concentration in the blood is very low. This test measures the total amount of IgE in the blood. Immunoglobulins are proteins that play a fundamental role in the body. They are produced by specific cells known as plasma cells in response to stimuli such as bacteria, viruses or other microorganisms, or to the presence of substances that the body does not recognize as its own (antigens).