Immunoglobulin E (IgE) is an antibody that plays an important role in the development of allergies, as well as in the body’s defense against parasites. The amount of IgE in the body can be elevated in allergies. Therefore, if an allergy is suspected, an IgE test is performed to determine the IgE level in the blood. But when is the IgE level too high? What are the most common causes of an elevated IgE level and how can the IgE level be lowered? Find out that and more here.
What is immunoglobulin E?
Immunoglobulins are proteins (proteins) and components of the body’s defense system, the immune system. Immunoglobulins are also called antibodies. Antibodies are produced by the immune system in response to foreign substances, so-called antigens. They are designed to fight pathogens and harmful foreign substances that enter the body. There are many different antibodies, which are divided into classes. One of these classes is formed by immunoglobulin E, also known as IgE. Each class of antibody has its own function in the immune system. For example, IgE is especially important in allergic reactions and in defense against parasites. Understanding laboratory values: A check of the most important abbreviations
Other immunoglobulins
In addition, there are other immunoglobulins that play a central role in human defenses:
- Immunoglobulin A (IgA) is found primarily in body secretions such as tear fluid, saliva, nasal mucus, and breast milk. It binds pathogens and triggers inflammatory reactions.
- Immunoglobulin M (IgM) is found in the blood and is produced upon initial contact with a specific pathogen. This process is called the primary immune response.
- Immunoglobulin G (IgG) is a so-called secondary antibody and forms the main part of the antibodies in the blood. It is produced during repeated contact with a specific pathogen. IgG causes the scavenger cells (macrophages) to destroy the pathogen. This is called a secondary immune response.
How does an allergy develop?
In an allergic reaction, the immune system reacts to antigens from the environment that are actually harmless. The allergy-triggering antigens are also called allergens. Possible allergens include:
- Pollen
- Food
- House dust mites
- Animal hair
- Nickel
- Latex
What role does IgE play in allergic reactions?
In certain allergic reactions of the so-called immediate type (type I), a reaction occurs within a few seconds to minutes after contact with the allergen. IgE, which drives the allergy-related inflammatory process, is responsible for this rapid type of reaction. IgE initiates the release of the neurotransmitter histamine, which can lead to typical symptoms such as swelling, itching and redness. In addition to the immediate type, there are also type II (cytotoxic type), type III (immune complex type) and type IV (late type) allergies. The division into these four allergy types was developed by two immunologists in the early 1960s and is still valid today.
What is an IgE test?
In certain cases, a doctor may perform an IgE test. This is a blood test in which a blood count is taken and blood levels are determined with respect to IgE. An IgE test may be useful for two reasons:
- Because there is a specific IgE type for each antigen, testing for IgE types can be used to determine which antigen has caused an allergic reaction. For this purpose, an allergy test, more specifically an antigen-specific IgE antibody test, is performed.
- With the aim of determining the total amount of IgE in the blood, the total IgE value or total IgE value is determined. The total IgE level can increase due to parasite infestation or allergic reaction and is rarely too low.
IgE test – which immunoglobulin E type is present?
If one would like to clarify which allergens have led to a certain allergic reaction, the allergen-specific IgE antibodies can be determined by means of IgE testing. With the help of this blood test, the exact allergy type (for example, grass pollen allergy, mold allergy, house dust mite allergy and others) can be determined. In this way, allergy-causing substances can be avoided in the future or appropriate treatment of the allergy can be initiated by the doctor.
How the IgE test works
The IgE test is performed using a small amount of blood from the affected person. Both the immunoglobulin E types and the total amount of IgE (total IgE value) are determined in the blood sample. Depending on the level of total IgE in the blood, a classification is made into different classes. Here, the lowest class (class 0) means that there is no allergy, and the highest class (class 6) indicates a strong allergy.
What is a normal IgE level?
The amount of total IgE depends on age. Children have a much lower level than adults. The value increases in the first ten years of life and is maintained in adulthood. The IgE value is measured in U/ml, which stands for units per milliliter of blood serum, or in µg/l, which means micrograms per liter of blood serum. The following IgE levels (total IgE) are considered normal:
- Adults: up to 100 U/ml (240 µg/l).
- Infants (1 to 3 years): up to 50 U/ml (120 µg/l).
- Babies (up to 1 year): up to 10 U/ml (24 µg/l).
IgE levels in an allergy test.
In an allergy test, not only the IgE type is determined, which indicates a specific allergen and thus allows conclusions to be drawn about what one is allergic to. In addition, the amount of allergen-specific IgE antibodies is also measured. This provides information about how strong an allergy to a specific allergen can be. For this purpose, a blood sample is examined with the help of a special laboratory test. The so-called Radio-Allergo-Sorbent-Test, in short RAST, is a method to determine and classify the amount of allergen-specific IgE antibodies. An alternative to this is the CAP test (carrier polymer system test), which is considered somewhat more modern, but provides comparable results to the RAS test. In total, there are six so-called RAST classes or CAP classes.
| RAST class | IgE (U/ml) | Result / Evaluation |
|---|---|---|
| 0 | < 0,35 | Lower detection limit |
| 1 | 0,35 – 0,70 | Borderline / questionable relevance |
| 2 | 0,71 – 3,50 | Slightly increased / relevance possible |
| 3 | 3,60 – 17,50 | Moderately elevated / relevant |
| 4 | 17,60 – 50,00 | Strongly increased / relevant |
| 5 | 50,10 – 100,00 | Very strongly increased / relevant |
| 6 | > 100,00 | Very strongly increased / relevant |
The results of the RAST alone do not provide any information as to whether or not an allergy is actually present. To prove or exclude an allergy, the medical history (patient interview) and the results of other tests, such as a skin test, the so-called prick test, must always be taken into account and evaluated. Deviations from all the above reference values do not necessarily indicate health problems. Therefore, it is advisable to always discuss individual blood values with the attending physician.
Immunoglobulin E elevated – what are the causes?
If the total IgE value is elevated, i.e. the total amount of immunoglobulin E in the blood, this may indicate a type I allergic disease or a parasite infestation. Specific possible causes include:
- Allergic asthma
- Allergic rhinitis, also hay fever
- Allergic conjunctivitis
- Insect venom allergy
- Food allergy
- Worm infestation
Total IgE levels are also frequently elevated in certain forms of atopic dermatitis and hives. In addition, a high value of IgE can also be a sign of the rare hyper IgE syndrome (HIES), a congenital chronic disease in which the immune system is affected. However, this disease occurs in only about one in 100,000 people. Incidentally, IgE levels that are too low are usually not problematic. Only in very rare cases are congenital immunodeficiencies, bone marrow diseases or kidney diseases (nephrotic syndrome) the reason for an IgE level that is too low.
Treatment: what to do for elevated immunoglobulin E?
The original task of immunoglobulin E, as a component of the immune system, is to recognize and eliminate foreign substances in the body. To perform this task, the amount of IgE increases when allergens are recognized. A high IgE level is the result.However, this increase in IgE is not always desired, for example in the case of an allergy. The IgE level and thus the allergic reaction can be lowered in different ways:
- Avoid known allergens: If no allergenic substances are present, the allergic inflammatory process is slowed down, because less IgE is released.
- Accustom the body to the allergens: For this purpose, the so-called hyposensitization. Here, the allergens are regularly injected in increasing doses by the doctor under the skin of the patient or administered orally. The latter is called sublingual immunotherapy.
- Neutralize IgE with an antibody to IgE: This form of treatment is also called anti-IgE and is administered only in certain cases.
Important: The level of IgE is not directly related to the severity of allergy or parasitic infestation. It can equally happen that allergy symptoms are present, but the IgE level is not significantly elevated. Similarly, the IgE level may be elevated but allergy is not present. In this case, the elevated IgE level may have other causes, as described earlier.
Anti-IgE – what is it?
Anti-IgE is an antibody against immunoglobulin E. The man-made anti-IgE antibody omalizumab is currently used as an add-on therapy for severe allergic asthma and hives to suppress the IgE-mediated allergic response and thus symptoms. Omalizumab attaches to the IgE antibodies, preventing the allergic inflammatory process from occurring.