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  Back Blood-tests Explained


IgE, Total


At a Glance

Why Get Tested?

To screen for an allergic disease; sometimes to screen for a parasitic infection

When to Get Tested?

When you have periodic or persistent skin, lung, or digestive symptoms that suggest allergies; when a healthcare practitioner suspects a parasitic infection

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Immunoglobulin E (IgE) is an antibody that is produced by the body’s immune system in response to a perceived threat. It is one of five classes of immunoglobulins (A, G, M, D, and E) and is normally present in the blood in very small amounts. This test measures the amount of IgE in the blood.

Immunoglobulins are proteins that play a key role in the body's immune system. They are produced by specific immune cells called plasma cells. Immunoglobulins are produced in response to bacteria, viruses, and other microorganisms as well as substances that are recognized as "non-self" or present harmful antigens to the immune system.

Immunoglobulin E is associated with allergic responses, including asthma, and to a lesser degree with immunity to parasites. With allergies, the body overreacts to one or more substances in the environment called allergens that do not typically cause a response in other people. Someone may develop an allergy when that person is exposed to an allergen, such as plant pollen, peanuts, eggs, strawberries, bee venom, and hundreds of other potential substances.

During an initial exposure, also called sensitization, an allergic person produces an IgE specifically directed against that allergen. IgE binds to specialized white blood cells, resulting in the release of a number of substances, including histamine. In allergic/asthmatic people, this can cause constriction of the bronchi in the lungs. These substances are also responsible for the running nose, itchy eyes, and skin itching that occur in people with allergies.

Each time an allergic person is exposed to a specific allergen(s) after the initial exposure, IgE is rapidly produced, increasing to levels that trigger an allergic reaction. The severity of the reaction and symptoms associated with each episode can range from a localized reddening and itching of the skin, to respiratory distress, to vomiting and diarrhea, and in some cases to life-threatening anaphylaxis. Severity will vary from person to person, can vary from episode to episode, and may worsen over time.

The total IgE test measures the overall quantity of immunoglobulin E in the blood, not the amount of a specific type. It can be used to detect an allergic response in the body rather than a specific allergy. This test may compliment the information provided by allergy tests that detect allergen-specific IgE.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

The total IgE test may be used to help screen for and detect allergic diseases. It measures the overall quantity of immunoglobulin E in the blood. It may be ordered by itself, before, or along with allergen-specific IgE tests, depending upon whether or not a person or healthcare practitioner has identified potential substances to which the person may be allergic.

Immunoglobulin E (IgE) is an antibody that is produced by the body's immune system in response to a perceived threat. It is one of five classes of immunoglobulins and is normally present in the blood in very small amounts. IgE is associated with allergic responses, including asthma, and to a lesser degree with immunity to parasites. (For more, see the "What is being tested?" section.)

IgE can be increased with parasitic infections, so a total IgE test is sometimes used as a screening test if a parasitic infection is suspected.

When is it ordered?

A total IgE test may be ordered when a person has periodic or persistent symptoms that may be due to an allergic reaction, especially when the potential allergen is unknown. Symptoms may include those that suggest skin, respiratory, and/or digestive involvement, such as:

  • Periodic or persistent itching
  • Hives
  • Itchy eyes
  • Eczema
  • Nausea, vomiting, persistent diarrhea
  • Sneezing, coughing, congestion
  • Difficulty breathing
  • Asthma symptoms: wheezing, breathlessness, coughing, tightness in the chest

Sometimes an IgE may be ordered as a screening test when a person has persistent diarrhea that may be due to a parasitic infection. In addition, a complete blood count (CBC) with white blood cell differential may be ordered to determine if the number of eosinophils is increased.

What does the test result mean?

An increased total IgE level indicates that it is likely that a person has one or more allergies. Allergen-specific IgE levels will increase after an exposure and then decline over time, thus affecting the total IgE level. If a person is allergic to a seasonal substance, such as pollen, then both the specific IgE and total IgE would be expected to increase during the time of year when the allergen is present. If someone has one or more food allergies, then the total IgE level would mirror exposures to these foods. If someone is allergic to something that they are constantly around, such as mold in a house or cat dander, then the total IgE level may be persistently increased.

An elevated level of total IgE indicates an allergic process is likely present, but it will not indicate what a person is allergic to. In general, the greater the number of things a person is allergic to, the higher the total IgE level may be. An IgE elevation can also indicate the presence of a parasitic infection but cannot be used to determine the type of infection.

A normal IgE level makes it less likely that a person has allergies but does not rule them out due to the length of time between exposures. In between exposures, a person's IgE level may drop.

Sometimes an individual has a condition that affects the immune system and will not produce normal amounts of immunoglobulins. In this case, a person could have an allergy that is not reflected by the total IgE test result.

Is there anything else I should know?

In order to identify specific allergies, a healthcare practitioner must order tests that detect allergen-specific IgE. If a person is suspected of having an allergy to cats, then a cat dander IgE test must be ordered. If the person actually has an allergy to dogs, it will not be detected with this test. For this reason, healthcare practitioners may screen with a total IgE test, then run panels of substance-specific IgE tests. These panels may include a range of common allergens or similar types of allergens, such as various grasses, pollen, molds, pet dander, and/or foods.

A person's symptoms during an allergic episode do not necessarily correlate with that person's total IgE level.

Infrequently, an IgE test may be ordered to help diagnose a very rare inherited disease called hyperimmunoglobulin E syndrome (Job syndrome). People with this disease often have significantly higher than normal IgE levels and may have eczema, recurrent sinus and lung infections, bone defects, and severe skin infections. A greatly increased IgE concentration may indicate that an individual has inherited this condition. Additional testing can be performed to detect a mutation in the STAT3 gene that has been associated with this disorder.

Rarely, the IgE test is used to help diagnose and monitor multiple myeloma that produces monoclonal IgE.



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