​The measurement of total IgE levels has become well established in the investigation of allergic patients. Although IgE has the lowest concentration of all the Immunoglobulins, it has an extremely important role from a clinical standpoint because of its central involvement in allergic disorders. IgE is a monomer, with a molecular weight of 190,000 kDa and a serum concentration of 0.05 mg/dl. The serum concentration of IgE is significantly elevated in patients suffering from extrinsic asthma, hayfever and atopic eczema. IgE levels can also be raised in certain parasitic infections, some forms of immunodeficiency and bronchopulmonary aspergillosis.