IgE or immunoglobulin E is an antibody involved in the classic allergic reactions (type I reactions). It can be measured in a blood analysis.
Everybody has IgE; the levels are raised until the age of 18 years, and then remain stable. Levels that are normal for adults or older children can be very high for infants or younger children.
A high level of serum total IgE is often interpreted as the general tendency, the predisposition to develop allergic diseases. Nevertheless some people with high total IgE will not develop allergy; on the other side, some people with normal levels can even so develop an allergy.
Allergy is, by far, the most frequent disorder associated to high total IgE, but it is not the only one, as there are other rarer disorders with high IgE. Some parasitic infestations, infections by fungi, bacteria or virus, skin diseases, malignancies, immunodeficiencies, and other disorders are associated to high IgE.
There is a type of immunodeficiency called HyperIgE syndrome with very high levels of total IgE; some patients with allergy can, however, show as high levels of IgE without having an immunodeficiency.
Therefore, the interpretation of the results of IgE must be made considering the symptoms of the individual patient.
The results of the analysis are not influenced if the patient is receiving the medication usually administered in allergic diseases, such as antihistamines, inhalers, except for the use of anti-IgE monoclonal antibodies (omalizumab); this makes the interpretation difficult.
Serum total IgE does not mean that a patient is allergic to a specific substance, whether food or inhalant or others. This is investigated measuring the specific IgE.