Immunoglobulin E (IgE)
IgE is one of the 5 classes (isotypes) of antibodies. Like other immunoglobulins, it is produced by B cells and plasma cells. In contrast to other immunoglobulins, the circulating concentration of IgE is very low because B cells synthesize it at a very low rate and mast cells, basophils, and activated eosinophils bind up most of the circulating IgE. The normal concentration of IgE is only 0.05% of the IgG concentration.
In industrialized countries, allergy is the most common cause of elevated IgE concentrations, whereas in lesser-developed agrarian countries, parasitic infection is the most common etiology. The differential diagnosis of elevated IgE is summarized in the following table.
|
Category |
Examples |
|
Allergic disease |
Eczema, rhinitis, asthma, drug allergies, urticaria, extrinsic allergic alveolitis |
|
Cestodes |
Echinococcus granulosus & multilocularis |
|
Trematodes |
Schistosoma mansoni, japonicum & haematobium |
|
Nematodes |
Ascaris lumbricoides, Ancylostoma caninum & braziliense, Capillaria philippinensis, Toxocara cani & cati |
|
Monoclonal gammopathy |
IgE monoclonal gammopathy |
|
Immune deficiency syndromes |
Hyper-IgE, Wiskott-Aldrich, DiGeorge, Nezelof, Graft vs. Host, AIDS |
|
Inflammatory diseases |
Kawasaki, Periarteritis nodosa, Cystic fibrosis |
|
Infectious diseases |
Leprosy, Bronchopulmonary aspergillosis, Aspergilloma |
An elevated IgE level is not diagnostic of any condition because IgE levels are observed in many inflammatory and infectious diseases. An elevated IgE concentration supports the diagnosis of an allergic or parasitic disorder, but a normal IgE concentration does not exclude the diagnosis.
Total IgE antibody levels can be correlated with clinical allergy only in a general way. There is some evidence that elevated serum IgE levels in cord blood are predictive of subsequent development of atopy later in life. In infants, IgE levels greater than 20 U/mL support the diagnosis of allergic rhinitis. IgE levels in adults are less helpful in establishing an allergic etiology for symptoms. In adults, the likelihood of finding an elevated concentration of IgE varies directly with the number of allergens to which an individual is sensitized and the extent of allergic disease. For example it is commonplace to find an elevated IgE concentration in patients with atopic dermatitis, allergic rhinitis or asthma. Atopic disease is likely if the total IgE level is 375 IU/mL or greater. If the total IgE level is very low, atopic disease can usually be excluded.
Conversely, it is less common to find an elevated IgE level in a patient with immediate hypersensitivity to a single aeroallergen. Measurement of total IgE should not be used as a screening test for allergic disease. Patients with total IgE levels of 20 IU/mL or less rarely have detectable specific IgE levels.
Extreme elevations of 800 to 25,000 IU/mL are found in asthma associated with severe atopic dermatitis, allergic bronchopulmonary aspergillosis, parasitic infections, IgE myeloma, and Buckley syndrome.
IgE deficiency is difficult to define because normal IgE concentrations are so low. Immunoglobulin deficiency can be defined as IgE levels less than 2 U/mL in children and less than 4 U/mL in adults. Low IgE levels have been reported in severe combined immunodeficiency, hyper-IgM syndrome, ataxia telangiectasia, X-linked recessive Bruton agammaglobulinemia, and common variable immunodeficiency.
Generally, adult levels of IgE are achieved by 5 to 7 years of age. Between the ages of 10 and 14 years, IgE levels may be higher than in adults. After age 70 years, IgE levels may decline slightly. Reference range is 0 - 99 IU/mL. One unit equals 2.4 ng.
Specimen requirement is one SST tube of blood.
